Mechanical & Electronic Fuze

DELTA M137 MOD 3 Next Generation Electronic Fuze

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Chapter 1: AN INTRODUCTION TO MECHANICAL AND ELECTRONIC FUZES

CONTENTS • • • • • •

1.1.Introduction 1.2.Functions of Fuzes 1.3.History of Fuzes 1.4.Classification of Fuzes 1.5.Components of Fuzes 1.6.Closure 2

Chapter 2: Design of Fuzes CONTENTS • • • • • •

2.1 Introduction 2.2 Design Objectives for Fuzes 2.3 Approach to Fuze Design 2.4 Steps Involved in Fuze Design 2.5 Planning for Design of Fuzes at OFB 2.6 Closure

CHAPTER 1

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Chapter 3: Mechanical Fuzes CONTENTS • • • • • • • •

3.1 Introduction 3.2Fuze Initiation or Firing Mechanisms 3.3 Explosive Train 3.4 Safing Mechanisms 3.5 Arming Mechanisms 3.6 Features of Mechanical Fuzes 3.7Limitations of Mechanical Fuzes 3.8 Closure CHAPTER 2

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Chapter 4 : Electronic Fuzes CONTENTS • • • • • •

4.1 Introduction 4.2 Advantages of Electronic Fuzes 4.3 Basic Elements of Electronic Fuzes 4.4 Types of Electronic Fuzes 4.5 Limitations of Electronic Fuzes 4.6 Closure

CHAPTER 3

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Chapter 5 : Testing of Fuzes CONTENTS • • • • • • • •

5.1 Introduction 5.2 Development and Acceptance Tests 5.3 Component Tests 5.4 Proof Tests 5.5 Safety Tests 5.6 Surveillance Tests 5.7 Testing of Electronic Fuzes 5.8 Closure CHAPTER 4

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Chapter 6 : Futuristic Trends in Fuzes Technology

CONTENTS • 6.1 Introduction • 6.2 Latest electronic fuzes from leading manufacturers • 6.3 Innovations in Proximity Fuzing • 6.4 Innovations in fuze manufacture technology and safety mechanisms • 6.5 Future of Fuze technology • 6.6 Closure CHAPTER 5

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CONTENTS

• Bibliography • Appendix A: MIL-STD-331B • Appendix B: Schedule for Proof & Sentencing Criteri Fuze • Appendix C: Quality Assurance Procedure (Revised) For Fuze VT –8A (Electrical / Electronic) • Annexure 1 (to Appendix B)

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CHAPTER 1 FUZES: INTRODUCTION, FUNCTIONING AND CLASSIFICATION

1.1Introduction • Rockets, Missiles, Shells, Bombs and other ammunitions form an integral part of the firing capacity of an army in modern warfare. • These ammunition are filled with explosives with creates risk of explosion during handling, storage and launching. This necessitates the incorporation of some safety device in these ammunitions. Contents

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1.1 Introduction • Besides, it is required that when launched, the ammunition must fire at desired time and/or place in the enemy territory so that the intended purpose of inflicting damage on enemy target can be achieved with high precision and even selectively if required. • For this purpose, some mechanism must also be incorporated in the ammunition to sense the environment and initiate the ammunition.

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1.1 Introduction • The safety mechanism should work until the ammunition is launched and after the launch, the firing mechanism should take over. • In order to achieve this requirement, an arming mechanism is also required in the ammunition. All the abovementioned requirements of the ammunition are fulfilled by the devices called Fuzes. Contents

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1.2 Functions of Fuzes • Fuzes are the devices attached to ammunition for the purpose of safing, arming and firing. • Basic function of the fuze is to fire the ammunition when desired and ensure safety during other times. • Therefore, the fuze is also referred to as the brain of the ammunition. The basic functions of the fuzes are listed below

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1.2 Functions of Fuzes 1. Safing: To ensure safety during storage, handling (accidental mishandling), transportation and launching of the ammunition. 2. Arming: To sense the conditions of launch of ammunition and to align explosive trains, close switches and establish other links to enable the firing of ammunition thereafter. 3. Firing: To initiate the detonation in the ammunition at desired point in space or at preset time. 4. Fuze must be able to carry out abovementioned functional requirements reliably under extreme operational conditions such as high velocity, spin, environmental variables, impact etc. Contents

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1.3 History of Fuzes • The history of fuzes dates back to First World War, when primitive Direct Action fuzes having simple mechanical construction were developed (1914-17). • Prior to 1942, fuze system where entirely mechanical systems. Two types of proximity fuzes were developed during World War II, the radio and the photoelectric proximity fuzes.

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1.3 History of Fuzes • Photoelectric fuzes required light for operation and would sometime function early when sun moved into and out the field of view of the photoelectric lens. • For this reason, this fuze was discarded in 1943 and the term proximity or VT (Variable Time) fuze was used to refer to radio proximity fuzes. • Prior to early 1960s, the types of fuze used were either mechanical systems or hybrid systems containing electrical timing systems (vacuum tube units and other electrical components). Contents

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1.3 History of Fuzes • The first electronic hybrid (transistors and vacuum tubes) fuze, the M532, was made in early 1960s for a mortar round. • The first fully transistorized fuze, the M429, was made in the 1965-70 time-period for a 2.75” rocket. • The M514A1E1 (later named M728) was the first fully transistorized artillery fuze and was made in the late 1960s to early 1970s. • New electronic fuzes with multiple features came into existence in 1980s. Contents

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1.4 Classification of Fuzes • Fuzes can be classified into sub-categories based on their ammunition, tactical application, functioning, location etc. Some of such classifications are discussed below. Based on Functioning Based on the principle of operation, fuzes are classified as follows. • (i) Impact or Percussion Fuzes: Impact fuze initiates the firing action when actual contact with the target takes place. Impact fuzes are further classified as follows Contents

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1.4 Classification of Fuzes a) Point Detonating Fuzes (PD): Point detonating fuzes are located on the nose of the projectile and function upon the impact with the target or following impact with a timed delay. b) Base Detonating Fuzes (BD): Base detonating fuzes are located on the base of the projectile and function with short delay after the initial impact at the nose of the fuze. Contents

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1.4 Classification of Fuzes c) Point-Initiating, Base-Detonating (PIBD): Pointinitiating, base-detonating fuze has the targetsensing element in the nose of the projectile and the functional part of the fuze is in the base d) Delay Fuzes: These fuzes are designed to function after a long delay (minutes to days) after the initial impact. These fuze find their application in bombs, underwater mines etc. Contents

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1.4 Classification of Fuzes Point-detonating, Base-detonating, Point-initiating-Basedetonating and Delay fuzes are combined called as Direct Action fuzes as they function when something reasonably solid compresses the nose of the fuze. e) Graze fuzes: Many times, the projectile may land at the target at very low descent angles, resulting in a grazing action rather than a direct impact and the Direct Action fuzes may not function. Graze fuzes are designed for such cases. It detonates if the shell decelerates appreciably

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1.4 Classification of Fuzes • (ii) Time Fuzes: Time fuzes function at the end of an elapsed time after arming or impact. Time fuzes may further be classified based on the mechanism to measure time and induce delay such as mechanical, electronic, pyrotechnic, chemical, radiological etc. Time fuzes are used for illumination projectile and special purpose mines, bombs and grenades.

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1.4 Classification of Fuzes • In case the target is missed while firing from air-toair or ground-to-air, it is desired to destroy the projectile in the air itself. For such applications, Self-destruction feature in incorporated in fuzes known as Self Destruction (SD) fuzes, by using a suitable timing mechanism

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1.4 Classification of Fuzes • (iii) Proximity Fuzes: These fuzes function when they sense that they are in the proximity to the target. These fuzes are also called Influence fuzes. These fuzes are particularly effective in uses against personnel, light ground targets, aircrafts and superstructures of ships. The proximity sensor generally functions on the principle of Doppler effect. Contents

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1.4 Classification of Fuzes • (iv) Command Fuzes: Command fuzes are remotely controlled devices. Command fuzes function through a signal communicated to the fuze from a remote point through electrical, mechanical, optical or other means. • (v) Combination Fuzes: Fuzes involving more than one of the principles of operations discussed above are called Combination Fuzes. These fuzes have multi-options so that same fuze can serve for different tactical applications, with one mode of operation as Principle action and others as Secondary actions. Contents

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1.4 Classification of Fuzes 1.4.2. Based on types of mechanisms • Various mechanisms in the fuzes, such as safety, arming and firing, can be designed by using mechanical linkages or electrical / electronic circuits etc. Based on the mechanisms in the fuze, they are classified Mechanical Fuzes, Electronic Fuzes, Optical Fuzes, Chemical Fuzes etc. Mechanical and Electronic fuzes are discussed in detail in the subsequent chapters. Contents

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1.4 Classification of Fuzes 1.4.3. Based on the Tactical Application • Based on the tactical application, fuzes are classified as Air-to-Air, Air-to-Ground, Ground-to-Air and Ground-to-Ground.

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1.4 Classification of Fuzes

• • • • • • •

1.4.4. Based on the Purpose Based on the purpose of the fuze or the target, fuzes are classified as follows. Antipersonnel (APERS) Armor-Piercing (AP) Blast or High Explosive (HE) Concrete-Piercing (CP) High Explosive Anti-Tank (HEAT) High Explosive Plastic (HEP) Illumination Contents

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1.4 Classification of Fuzes 1.4.5. Based on Ammunition • Based on ammunition with which the fuze is employed, fuzes are classified as Bomb fuze, Grenade fuze, Guided Missile fuze, Mine fuze, Mortar fuze, Projectile fuze, Rocket fuze etc. • Type of ammunition and the fuzes used with them (based on the functioning) are given in the table below. Contents

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1.4 Classification of Fuzes S. No.

Ammunition

Fuzes Used

01.

Artillery Guns

Direct Action Fuzes (PD), Time Fuzes (M, El), Proximity

Mortars

Direct Action Fuzes (PD), Time Fuzes (M, El), Proximity Fuzes, Combination Fuzes, Delay Fuzes (Illuminating and

02.

Fuzes, Combination Fuzes.

Smoke Bombs). 03.

Naval Guns

Direct Action Fuzes (PD), Time Fuzes (M, El), Proximity Fuzes, Combination Fuzes. Naval Guns

04.

Tank Guns

Direct Action Fuzes (PD, PIBD), Graze Fuzes.

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1.4 Classification of Fuzes S. No.

Ammunition

Fuzes Used

05.

Bomb Fuzes

Direct Action Fuzes (PD), Time Fuzes (M, El), Proximity Fuzes, Combination Fuzes.

06.

Land Mines

Pressure Fuzes.

07.

Sea Mines

Time Fuzes (M, El), Delay Fuzes.

08.

Surface Target Missiles

Direct Action Fuzes (PD), Time Fuzes (M, El), Proximity Fuzes, Combination Fuzes.

09.

Air Target Missile

Direct Action Fuzes (PD), Time Fuzes (Self Destructive), Proximity Fuzes, Combination Fuzes.

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1.4 Classification of Fuzes S. No.

Ammunition

Fuzes Used

10.

Small Caliber Guns

Direct Action Fuzes (PD, BD), Proximity Fuzes, Combination Fuzes.

•M – Mechanical Fuze, •El – Electronic fuze, •PD – Point Detonating, •BD – Base detonating, •PIBD – Point-Initiating, Base-Detonating.

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1.5 Components of Fuzes • Many varieties of the fuze have been developed over the years in order to achieve specific functional objectives. • All of the fuses have some basic mechanisms/modules in common, though the working of mechanism may be markedly different. Some of the basic modules of the fuzes are discussed below Contents

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1.5 Components of Fuzes •

i)

1.5.1 Safety Mechanism: In order to provide adequate safety to the fuze, following safety features are incorporated in all the fuzes, though through different means. The present design philosophy entails the fuze to have at least two safing features, either one capable of preventing unintended detonation. The concept involved is that there is low probability of both the safety features failing simultaneously. Contents

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1.5 Components of Fuzes ii) Fuzes are designed to be detonator safe i.e. even if the detonator functions, it cannot initiate the explosive train prior to launch. The basic method to achieve this is by an interrupted explosive train, which aligns itself only after the launch of the ammunition. iii) Fuzes for artillery projectiles, mortar projectiles and rockets needs to be bore safe i.e. the detonator will not initiate a bursting charge while the projectile is in the launching tube. This is achieved by preventing initiating pin (firing pin) from hitting the detonator by introducing some interruption in between. Contents

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1.5 Components of Fuzes iv) A delay mechanism may be separately incorporated in some fuzes to delay the arming of the fuze until the ammunition has left the launcher. In other cases, the time taken by arming mechanism to arm the fuze or bore safety feature takes care of this requirement

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1.5 Components of Fuzes • 1.5.2 Arming Mechanism: Fuzes are designed to be bore safe and detonator safe for safety requirements. These feature needs to be disabled after the launch of the ammunition to complete the firing circuit and this objective is fulfilled by arming mechanism. • Arming mechanism mainly involves aligning explosive train elements or to remove the barriers in the explosive trains or to complete the firing circuit by closing switches. The energy to align the element and control the action time may be obtained from the forces experienced at the launch and during flight, or through any external source. Contents

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1.5 Components of Fuzes • 1.5.3 Explosive Train: Explosive train provides transition of a relatively feeble stimulus generated by initiating mechanism into the desired explosive output of the main charge. It consists of explosive elements arranged in the order of decreasing sensitivity. The initial explosive component is known as initiator, which may be a primer or a detonator. Contents

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1.5 Components of Fuzes • A primer may not detonate itself but causes detonation of the subsequent element in the explosive train whereas detonator detonates to generate an intense shock wave causing the detonation of subsequent elements. Delay elements may be provided in the explosive train to delay the propagation of detonation to the booster charge so that the ammunition can penetrate in the target. Contents

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1.5 Components of Fuzes • Relay elements may be provided to pick up the explosive stimulus from detonator, augment it and transmit it to the next element. • Leads transmit the detonation wave from detonator to the booster. Booster charge contains more explosive and it amplifies the detonation wave to a sufficient magnitude or maintains detonating conditions for a long enough time to initiate the main charge of the ammunition. Contents

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1.5 Components of Fuzes • 1.5.4 Firing Mechanism: Once the ammunition is armed, the fuze should initiate the explosion as per the performance desired of the ammunition. Ammunition may be required to explode after hitting the target or at a distance from the target or at preset time after penetrating the target or after recognizing some specified external circumstances. The firing mechanism of the fuze should initiate the explosion as per the design requirements. The target sensing mechanism of the fuze senses the target (or proximity to it) either due to impact or due to influence sensing (Doppler effect). Contents

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1.5 Components of Fuzes • A time fuze has a timer, which initiates the explosion after a preset time varying from few seconds to few minutes. Command fuzes initiate their ammunition on impulses received after launching. A combination of abovementioned methods is also used in fuzes for increased effectiveness and/or self-destruction. Once the target is sensed, the detonator of the explosive train is initiated by using firing pins or electrical stimulus generated by electrical or electronic circuits. Contents

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1.6 Closure • 1.6 Closure: • Fuzes are one of the most important components of the ammunition. Functioning and reliability of the ammunition depends upon the performance of the fuze. Basic requirements of the fuze are safing, arming and firing and it requires a great effort from the designer to incorporate the entire design feature within limited space. The design of fuze and steps involved in it are discussed in the next chapter. Contents

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CHAPTER 2 DESIGN OF FUZES • 2.1 Introduction: • Fuze is an example of complex modern design. • Design and development of fuze may initiate either because of requirement of the user (Defence Forces), • or because of some new brilliant idea or design developed by the designer resulting in better or improved fuzes for existing application CONTENTS

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2.1 Introduction • In the first case, the designer is provided with the functional objectives intended in the fuze and it is designer’s job to decide whether the objectives can be met by the improvement of an existing design or it necessitates development of a new fuze. • Designer has an idea of the physical parameters required for the fuze and he has to develop the fuze within the constraints mentioned in the user’s requirement. CONTENTS

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2.1 Introduction • In the latter case, the designer transforms his concept or design into a physical fuze, which performs a new function or satisfies some functional objectives in a better way than the existing designs. • The product is communicated to the supplying agency and the user, and based on their feedback and proofing results, the fuze is either developed further for production or is discarded. CONTENTS

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2.1 Introduction • • • • • • •

In either case, The designer must be thoroughly clear about the design objectives of the fuze, The environmental condition in which it will work, The safety features required, Tradeoffs permissible, Critical and non-critical design objectives, Economics involved, Scope of productionization etc. CONTENTS

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2.2 Design Objectives for Fuzes • The basic functional objectives of fuze may be broadly expressed as Safing, Arming and Firing, and performing the three functions reliably under all conditions. • However, there are many supplementary design objectives, which are seldom expressed explicitly. Essential design objectives of fuze are listed below.

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2.2 Design Objectives for Fuzes 1. Reliability of action. 2, Safety and resistance to deterioration in handling, use and storage. 3. Simplicity of construction. 4. Adequate strength in use and for accidental mishandling. 5. Compactness 6. Safety and ease of manufacture and loading. 7. Economy in manufacture. CONTENTS

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2.3 Approach to Design of Fuzes • Design of fuze is conceptually similar to design of any other device. Some of the essential ingredients involved in the design of fuze are as follows. 1.Detailed study of explicitly stated and implicitly involved design objectives and classification of objectives as critical (must required) and noncritical (desirable).

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2.3 Approach to Design of Fuzes 2. Developing of alternative means and systems to achieve design objectives. 3. Analysis of every alternative based on its capability to fulfill design objectives, resources required, cost involved, manufacturability etc. 4. Development of a mathematical or logical model i.e. a set of relations among the objectives, alternate means, environment and resources. CONTENTS

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2.3 Approach to Design of Fuzes 5.Selection of best possible design satisfying all the critical design objectives and most of non-critical design objectives and which are economically feasible and technically viable to manufacture

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2.4 Steps involved in Fuze Design • The first step in the design of fuze is to understand the fuze tactical requirements in detail and considering possible mechanisms or electrical/electronic circuits to meet them. • Based on the design objectives and constraints, the explosive train is established and basic arming, firing and safing mechanisms are selected. • Preliminary sketches are prepared keeping in mind the functionality of the fuze and manufacturability. CONTENTS

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2.4 Steps involved in Fuze Design • Next step is preparation of the drawings of every mechanism and component, which can be utilized for detailed design analysis. • All tactical, environmental, safety and design requirements of the fuze are reviewed critically. Forces acting on the fuzes are calculated, material is selected and the design is further refined. • Performance with this design is calculated and reliability of the design is estimated. • Finally, detailed drawing of the fuze is made indicating all dimensions, tolerances, and view. CONTENTS

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2.4 Steps involved in Fuze Design • Prototypes are made from the final drawing and are tested for their performance. • Trials depend on the type of fuze, severity of requirement, available time and funds. • The evaluation must be realistic and reliable. The components and sub-assemblies of the fuze are tested thoroughly individually and in assembled state. CONTENTS

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2.4 Steps involved in Fuze Design • Final step in fuze development is proof testing and acceptance testing. • A sample is selected from the pilot lot and is tested in actual ground conditions. The functioning and reliability of the fuze is assessed and it is either accepted for mass production or is returned to the designer for further development or is discarded.

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2.5 Planning for Design of Fuzes at OFB •

The design activity of fuzes at OFB can be planned in either or a combination of following modes ii) Through Reverse Engineering. a) In this method, an imported fuze is dissembled into all its components either at OF Khamaria or at OF Chanda, who have boiling facilities.

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2.5 Planning for Design of Fuzes at OFB a. The dissembled components are scanned to get the cloud points, which can be used to generate the solid model of the component. For this purpose, an agreement exists between OFB and CMERI, Durgapur, under which the components can be forwarded to CMERI and they provide with the cloud points.

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2.5 Planning for Design of Fuzes at OFB a. The CDDs (Center for Design and Development) at MPF, OFPM, OFC, RFI and OFAj are equipped with Imageware, a reverse engineering software, through which the output from CMERI is imported to obtain solid model in Unigraphics, which can give component drawings. b. The materials are assigned to the components by material testing of the components of the imported fuzes.

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2.5 Planning for Design of Fuzes at OFB i. b. c. d. e.

Through Re-engineering. Formulation up to solid modeling is similar to the procedure mentioned above in reverse engineering. Materials are assigned by experience. Testing loads are assigned to simulate and use. After fixing “b” and “c”, finite element analysis is done by using analysis software ANSYS to find out the components are safe and will function under actual load conditions (Inertial loads, Thermal loads, Electromagnetic loads). ANSYS is available at all CDDs. CONTENTS

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2.5 Planning for Design of Fuzes at OFB iii Through Innovation over existing products • In this case, various alternatives are thought for achieving the intended function and the general scheme of an existing design can be altered. iv Through de-novo new designs • In this case, by using the existing knowledge base and, the principle and concepts already available through collateral applications, a new design is prepared. CONTENTS

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2.6 Closure • Fuze development is a continuous process. Even when one design is finalized and accepted, it may be required to modify it to incorporate more features into it or to increase its reliability. • The pace of development of defence equipments today is extremely fast and new fuzes are being continuously developed to meet the extreme functional requirements of new ammunitions. CONTENTS

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2.6 Closure • Prior to 1960s, mechanical and electrical fuzes were the only fuzes present. • From the last 3 decades, electronic fuzes are replacing mechanical and electrical fuzes from many of their applications. • Mechanical fuzes, their mechanism and their features are discussed in next chapter, which will be followed by the discussion of electronic fuzes in the Chapter 4. CONTENTS

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CHAPTER 3 MECHANICAL FUZES 3.1 Introduction • Mechanical fuzes have their safing, arming and firing mechanisms consisting mostly of mechanical components, linkages and mechanisms. • Due to their simplicity and ease of conceptualization, mechanical fuzes were the earliest fuzes developed and are still used with many types of ammunitions CONTENTS

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3.1 Introduction • There can be various ways in which, mechanisms in a fuze can be designed. Which design is superior depends on the function of the fuze and the perception of the designer. • In the following sections, different mechanisms commonly used in mechanical fuzes are discussed.

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3.2 Fuze Initiation or Firing Mechanisms • The function of fuze initiation mechanism or firing mechanism is to sense the target or environment, and to initiate detonation in the explosive train when the pre-specified external condition has been achieved. Therefore, fuzes have target sensors followed by initiating mechanism

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3.2.1 Target Sensing • Target sensing depends on the task assigned to the ammunition. Ammunition may be required to fire at different locations or time depending on the desired purpose. • It may be required to fire on impact, after penetrating the target, after preset time, at a distance from target or any other condition. • Target sensing methods used with mechanical fuzes are discussed below. CONTENTS

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(i) Sensing by contact • In this mode, fuzes initiate their action by contact with the target. By modifying the mechanisms, the fuze can be made to initiate as soon as the impact takes place or after a time lag so that the ammunition penetrates the target. • Initiation of such fuzes is usually activated by the mechanical action resulting from contacting the target, for example, by moving a firing pin, by closing a switch etc. CONTENTS

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(i) Sensing by contact • Contact sensing can be applied in variety of ways. It can be applied to initiate the burst on the target surface itself when the fuze touches the target (Point Detonating). • It can be used to initiate the firing from behind the ammunition when nose touches the target, so that some time lag is introduced before the firing and the ammunition penetrates the target (Base Detonating). CONTENTS

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(i) Sensing by contact • Contact sensing can also be used for initiating burst at a distance from the target, when nose senses the target, firing initiates at the base, for example, fuzes for High Explosive Anti-Tank (HEAT) ammunition (Point-Initiating, Base-Detonating).

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(ii) Presetting • This type of sensing is achieved by a time fuze. The fuze is designed to initiate at a fixed time after the launch. A mechanical clockwork system is usually employed for the purpose, which measure the time after the launch and initiates the fuze after a particular time has elapsed. However, the intervals of time are limited in mechanical fuzes depending on the clockwork mechanism used. The time at which fuze should function is determined by the type of target, distance of the target etc. CONTENTS

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(iii) Combination and Self Destruction • Combination fuze incorporates features of both impact fuze and time fuze. It functions either on impact to the target or after a particular time. The later option is also utilized for providing selfdestruction option especially for fuzes of ground-toair and air-to-air application

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3.2.3 Initiating Mechanisms • Once the target sensor informs the fuze to initiate the detonation, an initiating mechanism starts the detonation chain. • Many mechanisms with different operating principles have been developed for the purpose. These mechanisms require power to initiate the detonation chain and time delays.

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3.2.3 Initiating Mechanisms • In mechanical fuzes, the contact sensing (impact) or presetting (clockwork mechanism) is converted directly into mechanical movement of a firing pin, which in turn is driven either into or against the first element of the explosive chain. • Functioning delays are usually obtained by pyrotechnic delays, which form a part of explosive train. CONTENTS

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(i) Initiation by Stab • The principle involved in initiation by stab is that if a pin punctures the primer case and enters a suitable explosive charge, an explosion can be initiated. • The firing pin usually is made up steel and aluminum alloy and has the shape of a truncated cone.

Figure 3.1 Stab Initiator and Detonator CONTENTS

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(i) Initiation by Stab • A Stab detonator converts the mechanical impact of the initiator (firing pin) into detonating wave is shown in the Figure 3.1.

Figure 3.1 Stab Initiator and Detonator CONTENTS

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(ii) Initiation by Percussion • Contrary to initiation by stab, the firing pin does not puncture the primer case in initiation by percussion. Instead, the firing pin dents the case and pinches the explosive between the case and a metal anvil provided at the back.

Figure 3.2 Percussion Initiator and Detonator CONTENTS

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(ii) Initiation by Percussion • As the explosive is squeezed between the case and the anvil, its granular structure fractures and detonation wave is initiated. Percussion firing pins usually have a semi-hemispherical tip (Figure 3.2).

Figure 3.2 Percussion Initiator and Detonator

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(iii) Initiation by Adiabatic Compression • This type of initiation does not require any firing pin. On impact with the target, an air column undergoes adiabatic compression resulting in temperature rise, which can be used to detonate the explosive charge (Figure 3.3).. Figure 3.3 Initiation by Adiabatic Compression

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(iii) Initiation by Adiabatic Compression • Though simple in construction, this fuze is neither sensitive nor reliable at low velocities and thin targets, and is therefore seldom used.

Figure 3.3 Initiation by Adiabatic Compression

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(iv) Initiation by Friction • Heat generated by friction can be used to detonate explosive charge in a fuze. The friction may be generated by rubbing two surfaces together, an example of which is a wire coated with friction composition pulled through an ignition mix (Figure 3.4) Figure3.4 Initiation by Friction

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Simple firing mechanism • A simple firing mechanism of a mechanical direct action fuze is shown in the Figure 3.5. Due to impact with the target, the firing pin extension moves downwards forcing the firing pin into the detonator and thus initiating the explosive train.

Figure 3.5 Simple Firing Mechanism

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3.3 Explosive Train • Explosive train amplifies a relatively weak stimulus by initiating mechanism to detonate the main charge. It is an assembly of explosive elements arranged in the order of decreasing sensitivity

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3.3.1 Classification of Explosives • Explosive materials are chemical substances, which can undergo rapid chemical change without an outside supply of oxygen, and with the liberation of large quantities of energy generally accompanied by the evolution of hot gases. These are mixtures of certain fuels of extremely high calorific value and oxidizers

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3.3.1 Classification of Explosives • Explosives are classified as Low explosives and High explosives. Low explosives are those in which the advance of chemical reaction into the unreacted explosive is less than the velocity of sound through the undisturbed material. Low explosives normally burn and deflagrate rather than detonate. Low explosives may be gas producing or non-gas producing. Due to their low rate of detonation, these are not usually employed in the fuze explosive trains. CONTENTS

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3.3.1 Classification of Explosives • On the other hand, High explosives are those in which the advance of chemical reaction into the unreacted explosive exceeds the velocity of sound through this explosive. • High explosives are further classifies as Primary and Secondary. Primary high explosives are sensitive in initiation by both heat and shock (e.g. lead azide, lead styphnate, diazodinitrophenol, hexanitromannite). CONTENTS

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3.3.1 Classification of Explosives • Therefore, these explosive form the initial elements of the explosive trains. Secondary high explosive are not readily initiated by heat or shock but rather by an explosive shock from a primary explosive (e.g. PETN, RDX, tetryl, TNT, picatrol etc.). These explosive form the delay elements, relay elements and booster charge in the fuze.

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3.3.2 Elements of an Explosive Train • An explosive train consists of some initial elements (primer, detonator etc.), which amplify the weak stimulus provided by the initiator, and other explosive elements (delay elements, relay elements, booster charge etc.), which sustains and transmits the amplified stimulus to the explosives in the shell. • These elements of the explosive train are discussed in further detail in the following sections CONTENTS

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3.3.3 Initial explosive components • Initial explosive components of the explosive train are generally primer and detonator, and are also referred to as initiators. A primer is a relatively small, sensitive explosive component, which serves as an energy transducer, converting mechanical or electrical energy into explosive energy. • The explosive output is relatively small and is further amplified and sustained by later elements of the explosive train. Primer may not detonate itself but may induce detonation of the successive elements CONTENTS

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3.3.3 Initial explosive components • A detonator is a small sensitive component capable of reliably initiating high order detonation in the next high explosive of the explosive train. • It differs from the primer in that its output is an intense shock wave. It can be initiated directly by mechanical or electrical means, or by the output energy of the primer.

CONTENTS

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3.3.3 Initial explosive components • Typically, initiators and detonators have three charges: a priming charge, an intermediate charge and a base charge, although two of these charges can be combined. • Priming charge is similar to primer and is generally made of lead azide or lead styphnate. Intermediate charge is usually lead azide while the base charge can be lead azide, PETN, tetryl or RDX. CONTENTS

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3.3.3 Initial explosive components • i)

Based on the initiating mechanisms, initiators can be of following types. Stab initiators: It consists of a cup loaded with explosives and covered with a closing disc (Figure 3.1). It is sensitive to mechanical energy and is initiated by puncturing the cup.

Figure 3.1 Stab Initiator and Detonator

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3.3.3 Initial explosive components ii) Percussion primers: It consists of a cup filled with a thin layer of primer mix and an anvil on the other side (Figure 3.2). When the firing pin hits the cup, the primer mix is squeezed between the cup and the anvil, and the detonation starts. Thus, percussion primers fire without puncturing the cup Figure 3.2 Percussion Initiator and Detonator CONTENTS

92

3.3.3 Initial explosive components •

•

Flash detonators: They are similar to stab initiator but they are sensitive to heat and initiate due to heat generated by mechanical impact Electrical Primer and detonators: These initiators function as a result of detonation of a spot charge in the primer due to passage of electrical energy through it.

CONTENTS

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3.3.3 Initial explosive components • The input to the initiator may be mechanical energy, electrical energy or some other kind of energy input. • The output of the initiator may be a shock wave, a flame, hot gases etc. Selection of a suitable initiator depends on the design features of the fuze and the initiation properties of the other elements of the explosive trains.

CONTENTS

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3.3.4 Booster Charges • This is the last element of the explosive train and it contains more explosive than any other element. The booster charge is initiated by one or several leads or directly by a detonator. It amplifies the detonation wave to a sufficient magnitude and maintains detonating conditions for long enough time to initiate the main charge of the ammunition. The most common explosives for booster are Tetryl, RDX, granular TNT, RDX –wax mixture and PETN. CONTENTS

95

3.3.5 Other explosive elements • Some other explosive elements of the explosive train are employed to sustain and amplify the output of the initiators, and to pass it to booster charge. Some of these elements are discussed below

CONTENTS

96

3.3.5 Other explosive elements • •

Delay elements: Delay elements are incorporated into the explosive train to enhance target damage by allowing the missile to penetrate before exploding or to control the timing of sequential operations. Delay elements are the components providing time lag in the explosive train. Generally, delay column burns like a cigarette i.e. they are ignited at one end and burn linearly. CONTENTS

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3.3.5 Other explosive elements • Delay column are ignited by a suitable primer. Explosives used in delay elements can be classified as gas producing (e.g. Black powder) and Gasless mixtures (e.g. metallic fuel plus oxidant). A typical delay element is shown in the Figure 3.6.

Figure 3.6 Delay Elements

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3.3.5 Other explosive elements (ii) Relays: • Relays are small explosive elements used to augment and transmit the weak explosive stimulus of the initiator or delay element to the next components of the explosive train. Nearly all relays are loaded with Lead Azide, a primary explosive. Figure 3.7 Relays

CONTENTS

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3.3.5 Other explosive elements (iii) Leads • The purpose of the leads is to transmit the detonation wave from the detonator to the booster. Tetryl and RDX are the most common explosives for leads. The efficiency of the lead depends upon explosive density, confinement length and diameter

CONTENTS

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3.3.5 Other explosive elements • A simple explosive train in the fuze consisting of detonator, lead and booster is as shown in the Figure 3.8.

Figure 3.8 Simple Explosive Train (a) Unarmed state (b) Armed state CONTENTS

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3.4 Safing Mechanisms • The tactical requirements of a fuze necessitate the use of extremely sensitive explosive train, which responds to small impact forces, heat and electrical stimulus. • This introduces a very important design consideration while designing fuze: safety during manufacture, loading, transportation, storage, and assembly with the ammunition. CONTENTS

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3.4 Safing Mechanisms • Safety enters into every facet of fuze design and development. The present design philosophy entails the fuze to have at least two safing features, either one capable of preventing unintended detonation. • The concept is that there is low probability of both the safety features failing simultaneously. The main safety features incorporated in mechanical fuzes and mechanisms to achieve them are discussed below. CONTENTS

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3.4 Safing Mechanisms 3.4.1 Detonator Safe: Fuzes are designed to be detonator safe i.e. functioning of the detonator will not initiate subsequent explosive train components prior to arming. The basic method to achieve this is by an interrupted explosive train by mechanical separation or open switches.

CONTENTS

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3.4 Safing Mechanisms The interrupter should have a positive lock while in safe position. The detonator should be assembled in safe position so that fuze is safe during all final assembly steps and during subsequent handling.

CONTENTS

105

3.4 Safing Mechanisms • An example of detonator safe fuze is shown in the Figure 3.9.

Figure 3.9 (a) Fuze in Safe state

(b) Fuze in armed state

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3.4.2 Bore Safe: • Fuze must also be bore safe i.e. the detonator should not initiate the bursting charge while the projectile is in launching tube. • This can be achieved by the time lag required by the arming mechanism to function or by adding a separate time measuring device to delay the arming of the fuze until the ammunition has left the launcher CONTENTS

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3.4.2 Bore Safe: • Figure 3.10 gives an example of bore safe fuze by introducing a rotary shutter with a hole. The rotary shutter has a hole through which, the firing pin can strike the detonator. In the safe state, the hole in the shutter is out of line with the firing pin and detonator. .

Figure 3.10 (a) Fuze in Safe state

(b) Fuze in armed state

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3.4.2 Bore Safe: • After the firing, the shutter aligns itself with some mechanism to bring the firing pin, hole in the shutter and detonator in the same line. The fuze is now in armed state and will function on impact

Figure 3.10 (a) Fuze in Safe state

(b) Fuze in armed state

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3.4.3 Partial Arming Proof: • The fuze must never remain in the partially armed state. As soon as the force that cause the partial arming is removed, the fuze must return to the unarmed state. One-way to avoid partial arming is as shown in the Figure 3.11.

Figure 3.11 A mechanism to prevent partial arming CONTENTS

110

3.4.3 Partial Arming Proof: • Consider a plate loaded with a spring to prevent its rotation and is required to be rotated by 1800 to accomplish arming. Figure 3.11(a) shows the mechanism in unarmed state. Figure 3.11 A mechanism to prevent partial arming CONTENTS

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3.4.3 Partial Arming Proof: • An external force Fapp is applied to rotate the plate. Due to applied force, the plate rotates against the spring force and a restoring force Fres also acts on the plate. When the plate turns partially say 900 (Figure 3.11 b), the applied force is removed.

Figure 3.11 A mechanism to prevent partial arming CONTENTS

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3.4.3 Partial Arming Proof: • Due to the restoring spring force, the plate returns to its initial unarmed state (Figure 3.11 c). For arming, complete rotation of plate is required and therefore, applied force Fapp is applied throughout the rotation so that the plate cannot return back due to restoring spring force and is finally locked in the armed state (Figure 3.11 d, e, f).

Figure 3.11 A mechanism to prevent partial arming CONTENTS

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3.4.4 Arming Indicator: • An arming indicator is sometime provided in the fuze to indicate whether the fuze is in armed or unarmed state. • An anti-insertion feature may also be provided by which, the fuze cannot be inserted in their ammunition cavity if it has been accidentally armed.

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3.5 Arming Mechanisms • The arming process consists of aligning the elements of explosive train and/or in removing the barriers along the train. The main considerations in selection of a suitable arming mechanism are that sufficient energy should be available for the arming purpose and the arming should take place at a safe distance from the launcher

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3.5 Arming Mechanisms • The energy required for arming can be provided by the forces experienced by the fuze during launch or by some external energy source. These sources depend on the ballistic environment experienced by the fuze. These ballistic environments and energy sources are discussed in some detail in the subsequent sections

CONTENTS

116

3.5 Arming Mechanisms • The second objective can be met by incorporation of a time measuring device in the arming mechanism by which the arming can take place only after some time after the fuze has left the launcher and is at safe distance from it. • Sometime, the time involved in mechanism to function is itself large enough to satisfy the safety requirement during arming. Various mechanisms used for arming of fuze are discussed in detail later. CONTENTS

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3.5.1 Ballistic Environments • The energy available at the time of launch depends upon the ballistic conditions experienced by the fuze, which may be of following types: • high acceleration, • low acceleration • and gravity acceleration

CONTENTS

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3.5.1 Ballistic Environments • (i) High Acceleration: Projectiles fired from small arms, guns, howitzers, mortars, and rifles etc. experience acceleration of the order of ‘40,000g’ and are subjected to ballistic environment called High acceleration. Projectile launched with high acceleration may be either spin stabilized or fin stabilized.

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3.5.1 Ballistic Environments • Spin stabilized high acceleration projectiles are subjected to setback force, centrifugal force, tangential force and creep force. Fin stabilized projectiles are also subjected to all the forces mentioned above except those resulting from spin of the projectile (centrifugal forces).

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3.5.1 Ballistic Environments • (ii) Low Acceleration: Some projectiles (rockets) carry their own propellant and propellant is consumed during the flight. These ammunitions are thus launched with relatively lesser force and are subjected to ballistic environment called Low acceleration. There is not much setback force and hence, other forces are used for arming purposes.

CONTENTS

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3.5.1 Ballistic Environments • (iii) Gravity Acceleration: Airplane bombs are often dropped at a height and are subjected to acceleration equal to that of gravity. Fuzes for such ammunition experiences aerodynamic and barometric forces. So either of these force are utilized for arming or manual arming may be provide as in hand grenades

CONTENTS

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3.5.2 Energy Source for Arming: • Generally, the forces experienced during the launch of the ammunition (setback force) and flight (torque, centrifugal force, creep etc.) are large enough to fulfill the energy requirements of arming mechanisms. However, if the external forces are small or if their effect is comparable to that created by rough handling, a separate power source is provided in the fuze. Some of these energy sources are discussed below. CONTENTS

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3.5.2 Energy Source for Arming: • •

•

Setback: It is the relative rearward movement of the component in the ammunition undergoing forward acceleration during launch) Creep: It is the tendency of the components of the fuze to move forward as the ammunition slows down due to drag force by air friction and resistance during flight. Centrifugal force: This is the force experienced due to rotation of the spin-stabilized projectile during the flight. CONTENTS

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3.5.2 Energy Source for Arming: •

•

Tangential force: This is the force experienced by spring-loaded weights under the application of angular velocity. Coriolis force: It is the force experienced by a ball in a radial slot, which rotates at an angular velocity. This is seldom used for arming purpose.

CONTENTS

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3.5.2 Energy Source for Arming: •

•

Torque: It is the effect of force acting at a distance (by lever arm). It produces angular acceleration of a part. Forces of the Air Stream: This force is due to airflow past the propeller blades and is used to turn propellers in bombs and rockets.

CONTENTS

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3.5.2 Energy Source for Arming: viii) Ambient Pressure: Ambient pressure is very high at sea floors and can be used for arming in sea mines and depth charges. ix) Setforward: Setforward force is the reaction force experienced when the ammunition is rammed into an automatic weapon. It is opposite to setback force and acts in the direction of projectile travel.

CONTENTS

127

3.5.2 Energy Source for Arming: •

•

Sideways: Perfect alignment of projectile with the gun cannot be achieved practically. Thus, during launch, the projectile tries to align itself with the gun resulting in force called sideways. Non-environmental energy sources: When none of the above mentioned force is strong enough to provide necessary energy for arming of fuze, auxiliary power sources are provided. Springs may be used in compressed stage to store and deliver energy. Batteries may be used to turn a rotor or close a switch and cause arming. Explosives burn to produce heat and gases and the pressure developed by them can also be utilized for arming purpose. CONTENTS

128

3.5.3 Mechanical Arming Devices: •

i)

Fuzes operated by mechanical devices make use of mechanical linkages like springs, gears, sliders, rotors and plungers, or a combination of them. Some of these mechanisms are discussed below Springs: Springs provide a reservoir for stored energy, which can be conveniently accommodated in the fuze and can be used over the 20-year shelf life required for the fuze. CONTENTS

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3.5.3 Mechanical Arming Devices: • There are three general types of spring used in fuze arming mechanism. • The Flat Leaf spring is a thin beam, which creates tensile and compressive stresses when it bends. • The Flat Spiral spring wounds into a spiral and releases energy during unwinding. • The Helical Coil spring is a wire coil, in which shear stress is introduced when the coil is deflected. Various springs used with fuzes are as follows. CONTENTS

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3.5.3 Mechanical Arming Devices: (a) Belleville spring: This spring is normally used with land mines. When a force is applied in one of its equilibrium position, the spring flattens and moves rapidly to its other equilibrium position causing initiation.

Figure 3.12 Belleville Spring (a) Initial Position (b) Final Position (Firing) CONTENTS

131

3.5.3 Mechanical Arming Devices: (b) Power Springs: These are flat spiral springs used to drive clockworks and are also called mainsprings. Springs are usually contained in a hollow case to which one end of the spring is attached and the other end is attached to an arbor. (c) Hairsprings: These are special spiral springs which differ from power springs on two counts (i) the number of coil is large and space in-between in small, (ii) the spring is small. (d) Constant Force Springs: These are spiral springs, so wound that they provide constant force caused while unwinding. These are also called negators. CONTENTS

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3.5.3 Mechanical Arming Devices: ii) Sliders: Many fuze components such as interrupters and lock pins are basically sliders, which are moved by spring forces or inertia forces (setback, creep, centrifugal etc.). Sliders are usually held in their initial position using springs. Slider may move along the axis the of the fuze or perpendicular to it or at an angle to it.

CONTENTS

133

3.5.3 Mechanical Arming Devices: •

When the slider is to move along the axis of the fuze, it is held in initial position by a spring force and due to setback force experienced at launch, the slider moves within the ammunition against the spring force in accordance with the Newton’s law of conservation of momentum. When the slider is to move at an angle to or perpendicular to the axis of the fuze, it is held in initial position by lock pins and is driven either by spring force or by centrifugal force. CONTENTS

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3.5.3 Mechanical Arming Devices: iii) Rotary Devices: Rotary devices are pivoted so that they can turn through a specified angle only and the rotation may be caused by centrifugal forces, air stream effects or unwinding springs. These devices follow the general principle that the rotor turns until the moment of inertia of the rotor with respect to the ammunition spin axis is a maximum. Some of these devices are as follows CONTENTS

135

a) Disk Rotor: It rotates in a plane perpendicular to the axis of the fuze to align the firing pin and the detonator. (Figure 3.9)

Figure 3.9 (a) Fuze in Safe state

(b) Fuze in armed state

CONTENTS

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3.5.3 Mechanical Arming Devices: •

•

Centrifugal Pendulum: It is a bar pivoted at its center and rotates in a plane perpendicular to the axis of the fuze. Simple Plunger: This device operates by centrifugal forces and due to its asymmetry about the pivot, it releases with a preferred orientation to cause arming

CONTENTS

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3.5.3 Mechanical Arming Devices: d) Sequential Arming Segment: This device consists of series of pivoted segments held in position by springs. When a sustained acceleration occurs, each segment rotates through an angle causing the release of next segment and the rotation of the last segment disengages a spring held rotor to cause the arming action in the fuze

CONTENTS

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3.5.3 Mechanical Arming Devices: e) Rotary Shutter: It is an unsymmetrical disc pivoted at the center of the semicircular part and rotates due to centrifugal forces. Rotation of disc locates the hole such that the firing pin aligns with the detonator through the hole. An example of such shutter is shown in Figure 3.10.

Figure 3.10 (a) Fuze in Safe state

(b) Fuze in armed state

CONTENTS

139

3.5.3 Mechanical Arming Devices: f)

Ball Cam Rotor: It has a stationary part with a slot, a rotor with a spirally cut slot and a ball. The ball engages the rotor with the stationary part and due to the centrifugal forces, the rotor moves with a fixed angular velocity. Thus, this mechanism can be used to introduce mechanical time delays in the fuze.

Figure 3.13 Ball-Cam Rotor CONTENTS

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3.5.3 Mechanical Arming Devices: g) Ball Rotor: It is a ball having a detonator cavity, initially held in unarmed state by detents such that the firing pin and detonator cavity are misaligned. The rotation of the ball against centrifugal forces causes the alignment of firing pin and detonator cavity and hence the fuze is armed.

CONTENTS

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3.5.3 Mechanical Arming Devices: iv) Clockworks: Clockworks are mechanisms used to establish mechanical time delays in the fuzes. Clockworks have many parts but their principle parts are escapements and gear trains. Escapements are the regulators of the mechanical time fuzes while the gear trains are their transducers. It consists of a toothed wheel actuated by applied torque, a pallet with two teeth and a spring mass mechanism oscillating without any restoring force. CONTENTS

142

3.5.3 Mechanical Arming Devices: •

When the escape wheel turns, one pallet tooth is pushed along the escape wheel tooth and the other pallet engages the escape wheel. The same process is repeated every time the escape wheel turns and thus it acts as an oscillating system, which can be used as time counter. Clockwork mechanism can be used to arm the fuze only after it had travel safe distance from the launcher and for creating delayed initiation for time fuzes. CONTENTS

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3.5.3 Mechanical Arming Devices: v)Minor Mechanical Devices: Various minor mechanical devices such as pins, detents, links, knobs, levers, pivots etc serves various important purposes in the fuze. Pins are used for locking purposes and can be broken or moved for unlocking. Links are not desirable in the fuzes as they require space to operate but some links may be incorporated in fuzes to transmit motion from one part to another. CONTENTS

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3.5.3 Mechanical Arming Devices: • Detents are short rods whose purpose is to restrict motion of other member by exerting their shear strength. Knobs are used to select or set fuze functions. Levers are used to restrict the motion of another part by a locking action. Spiral unwinder system provides arming delays in fuzes due to effect of projectile spin.

CONTENTS

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3.6 Features of Mechanical Fuzes: The main features of mechanical fuzes are as follows. 2 Mechanical fuzes are simple in construction. Most of the components are simple mechanical links and can be easily designed and manufactured. 3 Mechanical fuzes can reliably operated in electromagnetic environment, where electronic fuze may malfunction due to electromagnetic interference (EMI). CONTENTS

146

3.7 Limitations with Mechanical Fuzes • 1

Mechanical fuzes have some limitations associated with it, which are discussed hereunder Mechanical fuze cannot function as proximity fuzes as there is no target sensing mechanism to sense a target at a distance and initiates the fuze.

CONTENTS

147

3.7 Limitations with Mechanical Fuzes 1

2

Mechanical fuze can be designed as time fuze, but the number of time interval options possible is limited. Besides, timing mechanisms are often of complicated design and are therefore undesirable for mass production. Time mechanisms require manual setting, which is undesirable for modern high firing rate weapons. Manual setting also introduces element of human error during setting and reduces reliability of the fuze Miniaturization is possible in mechanical fuze only to a limited extend, whereas the electronic fuzes can be designed into a compact miniaturized unit. CONTENTS

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3.8 Closure • Mechanical fuze were the first fuze developed mainly due to their simple construction and functioning. They have been serving their purpose effectively and efficiently for last century. However, the new requirements of modern warfare require intelligent fuzes, which can have more than one mode of operation. Electronic fuzes are the present generation fuzes that have replaced mechanical fuzes from many applications especially from time fuzes. These are discussed in detail in the next chapter

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CHAPTER 4 ELECTRONIC FUZES 4.1 Introduction • Basic functions of fuze are safing, arming, target sensing and firing. Mechanical Fuzes achieve these objectives by less accurate and unreliable mechanisms whereas Electronic fuze achieves these functions by means of electronic circuits or with a combination of both electronic circuits and mechanical mechanisms. CONTENTS

150

4.1 Introduction • In particular, safing and arming functions are combinely achieved by electronic and mechanical mechanisms. The target sensing and firing are achieved by electronic circuits. In this chapter, the advantages of electronic fuzes, basic elements of electronic fuzes and basics of different types of electronic fuzes are discussed.

CONTENTS

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4.2 Advantages of electronic fuzes • Necessity of electronic fuze basically arises from the limitations of other existing fuze systems. The conventional mechanical fuzes contain all the necessary systems for performing their function but the intelligence integrated in the fuze is absent. • Integration of electronics into fuze adds the required intelligence to the system and makes it more accomplished to do its job. Advantages of electronic fuzes over conventional mechanical fuzes are described below CONTENTS

152

4.2 Advantages of electronic fuzes i)

•

Proximity fuze action is possible only with electronic fuze. A great practical advantage of this type of fuze over conventional time fuze is that it relieves the gunner of the responsibility of fuze setting. He has to only ensure that ammunition passes within lethal range to the target and the fuze does the rest. CONTENTS

153

4.2 Advantages of electronic fuzes (ii) precise time setting with a wide discrete range, programmability and remote setting facility is possible with the advent of programmable electronic time (et) fuze. (iii) universal fuze gives user more flexibility to choose the fuze action as per his requirements. The universal fuze also helps the user to reduce inventory list as the same fuze can be used in many applications. CONTENTS

154

4.2 Advantages of electronic fuzes (iv) electronic fuzes are light-weight and compact as compared to conventional mechanical fuze. This gives extra space to fill the explosive. (v) electronic safety circuits are value additions to the overall safety of the fuze, making handling and transport easier and safer.

CONTENTS

155

4.3 Basic elements of electronic fuzes: • The basic electronic circuits and components required to make an electronic fuze are discussed in the following. (a) Antenna: This is generally a loop type antenna used to radiate the RF waves received from RF oscillator. Fuze body also forms a part of antenna and helps to radiate the RF waves. The design of antenna and fundamentals of wave propagation can be found in F.1 and F.2 of Bibliography. CONTENTS

156

4.3 Basic elements of electronic fuzes: (b) Radio frequency generator, transmitter and receiver: An oscillator circuit is used to generate the RF waves of required frequency, which are to be transmitted through antenna. This is a combined transmitter and receiver/detector, which sends out waves of radio frequency and receives them again after reflection from the target.

CONTENTS

157

4.3 Basic elements of electronic fuzes: • The interaction of the waves produces ripple impulses of audio frequency. The design principles of various communication systems can be studied in detail in F.3 and F.4 of Bibliography

CONTENTS

158

4.3 Basic elements of electronic fuzes: (c) Signal processor unit: This is generally an audio frequency amplifier circuit. This is called signal processor unit, as it amplifies the weak audio frequency signal received by detector. The output of signal processor unit is a trigger pulse, which is utilized by firing circuit to trigger its electronic switch. The detailed study of analog circuit and their design can be found in F.5 and F.6 of Bibliography. CONTENTS

159

4.3 Basic elements of electronic fuzes: (d) Electronic Time delay circuit: This is a counter based time delay circuit, which provides the necessary time delay after firing to the time of function of fuze. Depending on the requirement time delay circuit can be of simple or complex nature. Simple time delay circuit contains a single counter, which will have a fix count and hence a single time delay (e.g. fix 10 seconds ± tolerance) of specified amount can be achieved. CONTENTS

160

4.3 Basic elements of electronic fuzes: • If more than one-time delay options are required, multiple counter circuit with a selectable switch is required. For example, if one wants to have a fuze with a time delay options of 10 sec or 50 sec or 100 sec ± tolerance, then three counter circuit with a selectable switch would be required. Further if one wants a range of time delay e.g. from 0 sec to 200 sec ± tolerance, then a programmable counter circuit would be needed. CONTENTS

161

4.3 Basic elements of electronic fuzes: • The timer circuits can also be implemented on FPGA (Field Programmable Gate Array). FPGA can be used to implement any digital logic circuit required by user and as the name suggests it can be programmed at field i.e. by user at his requirement. The detailed study of various digital logic circuits and their design principles can be found in F.7 of Bibliography. CONTENTS

162

4.3 Basic elements of electronic fuzes: (e) Electronic safety circuit: This is generally an electronic time delay circuit which enables the firing mechanism after some specified time to ensure that fuze does not function prematurely in any case.

CONTENTS

163

4.3 Basic elements of electronic fuzes: (f) Power supply: Power supply is generally a reserve type of primary battery with the electrolyte contained in a glass ampoule, which is broken by set – back force on firing the gun. It acts as a safety mechanism as it prevents the electronic circuit from getting power and hence preventing any premature or accidental explosion. Air driven alternators are also used as source of power supply in electronic fuzes now a days. Air driven alternator utilizes the airflow in the fuze to generate the required electric voltage CONTENTS

164

4.3 Basic elements of electronic fuzes: (g) Impact switch: This switch is normally open while handling and transporting the fuze. It closes when fuze is fired and hits any hard object. This switch is placed in the path of condenser of firing circuit and electric detonator. When the switch closes, it allows the condenser to get discharge into electric detonator. It is a mechanical switch and is used in electronic point detonation fuze or in fuzes where point detonation action is required as back up mode if the fuze does not function in its set mode. CONTENTS

165

4.3 Basic elements of electronic fuzes: (h) Firing circuit: It consists of a grid condenser, electronic switch (Thyristor, or MOSFET transistor or thyratron), and electric detonator. The electric detonator is a bridge wire element some times also referred to as an electronic blasting cap. The bridge wire element consisted of small metal wire or a thin strip of carbon film in parallel with a total resistance value of about 700 to 15, 000 ohms. CONTENTS

166

4.3 Basic elements of electronic fuzes: • Electronic switch is closed on receipt of trigger pulse of appropriate magnitude from audio amplifier circuit and the grid condenser is discharged into electric detonator to initiate the explosive train.

Figure 4.1: Firing Circuit

CONTENTS

167

4.3 Basic elements of electronic fuzes: (i) Safety switch and mechanical arming/safety systems: The safety switch is used to connect the two entities on experiencing a force such as acceleration force of certain magnitude or spin of certain rpm or air flow of certain magnitude. This is a mechanical system, similar to one used in mechanical fuzes

CONTENTS

168

4.3 Basic elements of electronic fuzes: • To make a particular type of electronic fuze the required modules are implemented on Printed Circuit Board (PCB) and interfaced to have the required fuze action. The modules can be implemented in a single PCB or more than one PCB. The electronic modules are individually tested and then interfaced with the rest of the subassemblies to make the complete fuze. The complete fuze is then tested for the required performance parameters. CONTENTS

169

4.4 Types of electronic fuze • Depending upon the target sensing mechanism and electronic circuitry involved, the electronic fuzes are classified in following types. (i) Radio Proximity (PRX) Fuze (ii) Electronic Time (ET) Fuze. (iii) Electronic Point Detonation (EPD) Fuze. (iv) Universal Fuze

CONTENTS

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4.4.1 Radio Proximity (PRX) Fuze • The Radio Proximity Fuzes are also called Variable Time (VT) Fuze as the operation time varies with the range of the target. The proximity fuze is a selfcontained radio controlled fuze capable of transmitting waves of radio frequency, and of receiving a portion of these waves, which may be reflected by the target. The fuze fires when the returning signal is of sufficient strength, due to proximity to the target, to trigger the firing circuit. CONTENTS

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4.4.1 Radio Proximity (PRX) Fuze • Essentially, the fuze is an extremely rugged radio transmitting and receiving station, which fits into the nose of a projectile. The Radio PRX fuze may be defined as “A fuze wherein primary initiation occurs by remotely sensing the presence, distance, and/or direction of a target or its associated environment by means of a signal generated by the fuze or emitted by the target, or by detecting a disturbance of a natural field surrounding the target.” CONTENTS

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4.4.1 Radio Proximity (PRX) Fuze • The proximity fuzes are particularly very useful in ground to air and air to ground applications where the probability of hitting the target is less. Using proximity fuze increases the probability of target destruction as now we need to only bring the ammunition in the vicinity of target and fuze does the rest.

CONTENTS

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4.4.1 Radio Proximity (PRX) Fuze (i) Fundamental make-up: The radio proximity fuze basically consists of an antenna, oscillator/detector, audio frequency amplifier, electronic safety circuit, Power supply, firing circuit and other mechanical safety and arming sub-assemblies. The block diagram of a Proximity fuze is as follow.

CONTENTS

174

4.4.1 Radio Proximity (PRX) Fuze (ii) Working principle: Proximity fuzes functions on the principle of Doppler effect. The Doppler effect states that, if there is a relative motion between two objects then the frequency of reflected waves would be different from that of transmitted waves. If the two objects approach each other than the frequency of reflected waves is greater than that of transmitted waves and if they move in apposite direction than frequency of reflected waves is less than that of transmitted waves. The difference in frequency can be utilized to sense the target. CONTENTS

175

4.4.1 Radio Proximity (PRX) Fuze

Figure 5.2: Block diagram of a Proximity fuze. CONTENTS

176

4.4.1 Radio Proximity (PRX) Fuze • The working principle of the PRX fuze shown in block diagram is as follows. The power supply is activated only after firing the ammunition by utilizing setback force. The rest of the circuitry gets the power through safety switch and starts functioning.

Figure 5.2: Block diagram of a Proximity fuze. CONTENTS

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4.4.1 Radio Proximity (PRX) Fuze •

The proximity sensor unit (RF oscillator/detector) gets power after a delay as set in ‘Time delay unit’. This is to ensure that proximity sensor gets activated only in the later part of trajectory of projectile and hence reducing any possibility of jamming or influence from other electro-magnetic signals.

Figure 5.2: Block diagram of a Proximity fuze. CONTENTS

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4.4.1 Radio Proximity (PRX) Fuze •

The RF oscillator/detector generates the RF waves of required frequency, which are then transmitted by antenna. The radio waves travel at the speed of light in space. These waves will be reflected back to the oscillator by any target that gives a radio reflection, such as metal objects, water, or earth.

Figure 5.2: Block diagram of a Proximity fuze.

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4.4.1 Radio Proximity (PRX) Fuze •

The detector receives some of the RF waves reflected from the target. The transmitted and reflected waves interfere with each other to give a beat frequency. The amplifier circuit amplifies the beat frequency, which is in audio frequency range.

Figure 5.2: Block diagram of a Proximity fuze.

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4.4.1 Radio Proximity (PRX) Fuze •

The electronic safety circuit delays the path of power to reach firing circuit and hence delaying the firing condenser to get charged till a certain time is lapsed after firing the ammunition from the gun. This ensures safety during firing of ammunition and avoids any premature functioning of the fuze.

Figure 5.2: Block diagram of a Proximity fuze.

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4.4.1 Radio Proximity (PRX) Fuze •

The condenser is charged by power supply voltage before the firing circuit receives signal from audio amplifier, setting safety time in electronic safety circuit much less than the total flight time ensures this. Once the condenser is charged, the projectile is “armed” and ready to detonate when a target influences to do it so.

Figure 5.2: Block diagram of a Proximity fuze.

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4.4.1 Radio Proximity (PRX) Fuze • The output of amplifier is coupled to the electronic switch of firing circuit to trigger the firing mechanism of the fuze. At first the projectile is so far from the target that the strength of reflected waves and hence output signal of amplifier is too weak to trigger the firing circuit.

Figure 5.2: Block diagram of a Proximity fuze. CONTENTS

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4.4.1 Radio Proximity (PRX) Fuze • As the proximity fuze projectile approaches the target, the amplitude of the beat frequency produced in the detector circuit increases and hence the output of audio amplifier also increases.

Figure 5.2: Block diagram of a Proximity fuze. CONTENTS

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4.4.1 Radio Proximity (PRX) Fuze • When the projectile reaches a specified position relative to the target and hence the output of the audio amplifier reaches a certain level, the electronic switch of firing circuit is closed and the path between firing condenser and electric detonator is completed.

Figure 5.2: Block diagram of a Proximity fuze. CONTENTS

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4.4.1 Radio Proximity (PRX) Fuze • The firing condenser is discharged into the electric detonator dissipating sufficient energy to start the detonation process.

Figure 5.2: Block diagram of a Proximity fuze. CONTENTS

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4.4.2 Electronic Time (ET) fuze: • ET fuze uses electronic time delay circuits to introduce the delay between firing of the ammunition and its explosion. The electronic time delay circuits are implemented with the help of counter Integrated Circuits (ICs). The configuration of counter decides the delay time, which can be altered by changing the circuit parameters. Programmable counters with hand held setters are used now a days in modern ET fuzes. CONTENTS

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4.4.2 Electronic Time (ET) fuze: • ET fuze may be defined as “A fuze that contains a graduated time element to regulate the time interval after which the fuze will function.” Electronic Time (ET) fuze are used in applications where the range of the target is known and ammunition is required to function after a predetermined time & also in smoke and illumination rounds.

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4.4.2 Electronic Time (ET) fuze: (i) Fundamental make-up: The ET fuze basically consists of an electronic time delay circuit, electronic safety circuit, power supply, firing circuit, and other mechanical sub-assemblies. The block diagram of an ET fuze is as follows.

CONTENTS

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4.4.2 Electronic Time (ET) fuze:

Figure 5.3: Block diagram of an Electronic Time fuze CONTENTS

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4.4.2 Electronic Time (ET) fuze: (ii) Working principle: The power supply is activated by exploiting setback force. The safety switch hinders the path of power supply to electronic time delay unit and electronic safety circuit. Safety switch is closed either by setback force itself or by spin force of specified magnitude or by any other mechanism (it depends on design).

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4.4.2 Electronic Time (ET) fuze: • The safety switch is closed and the power is applied to electronic safety circuit and electronic time delay unit simultaneously. The ET fuze usually have two types of specifications for time delay one is the ‘safety time’ which is determined by the time setting of the electronic safety circuit and the other one is the ‘operation time’ which is determined by the time setting of the electronic time delay unit. CONTENTS

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4.4.2 Electronic Time (ET) fuze: • The ‘safety time’ and ‘operation time’ can be factory set or, if fuze is programmable, they can be set by user depending on his requirement. The electronic safety circuit stops the firing condenser of firing circuit to get charged for a specified safety time. When the specified safety time is lapsed, the electronic safety circuit enables the firing condenser to get power from power supply and charge to the required potential. The time delay unit starts counting as soon as it gets power from power supply.

CONTENTS

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4.4.2 Electronic Time (ET) fuze: • The factory set time or user set time (if the timer is programmable) is counted by the counter and upon lapse of this time interval time delay unit generates a trigger pulse. Trigger pulse is applied at the trigger input of the electronic switch of the firing circuit, which in turn closes the path between firing condenser and electric detonator. The energy stored in firing condenser is dissipated in the electric detonator, which starts the detonation process CONTENTS

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4.4.3 Electronic Point Detonation (EPD) Fuze • EPD fuze is the simplest type of electronic fuze. It functions when the projectile hits any hard object. The impact switch acts as the target sensor i.e. as soon as projectile hits the target the switch closes and causes detonation. EPD fuze action is also used as a back up mode in most of the modern Proximity and Electronic Time fuzes to ensure that if fuze does not function in its set mode (PRX or ET) than it functions at least on hitting some hard object. Electronic point detonation fuze may be defines as “A fuze that is set in action by the striking of a projectile or bomb against an object”. CONTENTS

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4.4.3 Electronic Point Detonation (EPD) Fuze (i) Fundamental make-up: The EPD fuze consists of impact switch, power supply, firing circuit, electronic safety circuit, and other mechanical subassemblies. Block diagram of an EPD fuze is as follows.

CONTENTS

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4.4.3 Electronic Point Detonation (EPD) Fuze

Figure5.4: Block diagram of an EPD fuze

CONTENTS

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4.4.3 Electronic Point Detonation (EPD) Fuze (ii) Working principle: The EPD fuze has very less electronics integrated in it. Electronic circuits perform only firing and safety functions. The power supply is activated by setback force as soon as the ammunition is fired. The electronic safety circuit counts the time and upon lapse of set time, it feed the power to firing circuit and the condenser of firing circuit gets charge by the power supply. CONTENTS

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4.4.3 Electronic Point Detonation (EPD) Fuze • Once this condenser is charged, the projectile is “armed” and ready to detonate when projectile hits a hard object. The impact switch closes when projectile hits an object and triggers firing circuit. The path between the firing condenser of firing circuit and electric detonator is closed by impact switch and energy stored in firing condenser is dissipated into the electric detonator, which then starts the detonation process. CONTENTS

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4.4.4 Universal fuze • The definition of Universal Fuze is not unique, one may define universal fuze in his own way. The idea of Universal fuze is to make a single type of fuze, which can be used in many applications. This provides user more flexibility in managing his inventory. The Universal fuze can be defined in terms of its applicability to multi caliber systems in same ammunition type, or applicability to multiple ammunitions, or both multiple caliber and multiple ammunitions. Following may be one set of universal fuze.

CONTENTS

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4.4.4 Universal fuze (i) Programmable Electronic Time Fuze with EPD back up: The programmable ET fuze can be used in multiple caliber ammunitions since the user has the luxury to set the operation time depending on caliber of ammunition. With programmability of operation time, it also has EPD mode as back up or option to set EPD as operation mode

CONTENTS

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4.4.4 Universal fuze (ii) Programmable Proximity Fuze with EPD backup: The programmable PRX fuze can be used in multiple caliber ammunitions since the user has the luxury to set the Height-of-Burst, depending on caliber of ammunition. With programmability of Height-of-Burst, it also has EPD mode as back up or option to set EPD as operation mode

CONTENTS

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4.4.4 Universal fuze (iii) Multi-Option Fuze (MOF): The Multi-Option fuze has all three modes of operation: Proximity (PRX), Electronic Time (ET) and Electronic Point Detonation (PD). The EPD mode can be selected as operation mode or it can be set as back up mode with PRX or ET mode. The user has the luxury to select the operation mode either PRX or ET with or with EPD back up or EPD mode only as operation mode. CONTENTS

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4.4.4 Universal fuze • In ET mode, the operation time can be set by the user, making it useful in all caliber ammunitions. Similarly, in PRX mode the Height-of-Burst can be set by user, making it useful in all caliber ammunitions. Block diagram of a typical MultiOption Fuze is as follows.

CONTENTS

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4.4.4 Universal fuze

Figure5.5: Block diagram of Multi-Option Fuze CONTENTS

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4.4.4 Universal fuze 4.4.4.1 Working Principle: Multi-Option Fuze (MOF) is a combination of all three fuze action, i.e. proximity, time and point detonation. The basic construction has all the components used in PRX, ET and EPD fuzes along with other components such as ‘Selector Switch’, ‘Height-of-Burst Setter’ and ‘Time Setter’.

CONTENTS

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4.4.4 Universal fuze •

The selector switch can be an electronic switch implemented with the help of a de-multiplexer or a manual one to many electrical switch. The selector switch is used to select the operation mode of the fuze. There are three possible operation modes in this fuze viz. ii) Proximity with EPD back up, iii) Electronic Time with EPD back up, iv) And Only EPD. CONTENTS

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4.4.4 Universal fuze • Selecting one of these operation modes, the path of power supply to the corresponding circuit module is activated by selector switch via safety switch (except in case of EPD, where no power is required). The function of safety switch is same as explained in PRX and ET fuze. Depending on the mode selected, the corresponding circuit module (proximity sensor or programmable time delay unit) gets power and starts functioning. CONTENTS

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4.4.4 Universal fuze • The principle of working of PRX sensor and Electronic Timer is same as explained in PRX fuze and ET fuze respectively, the only difference being is that, in case of MOF fuze electronic timer is programmable and hence operation time can be set by the user. The ‘operation time’ is set with the help of ‘Time Setter’ unit. Time Setter unit can be a part of fuze or it can be a separate entity. CONTENTS

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4.4.4 Universal fuze • Similarly ‘Height-of Burst Setter can be a part of fuze or it can a separate entity. Making it a separate entity has the advantage that only one setter can be used for many fuzes and hence saving the cost. The working principle of rest of the components of MOF fuze is same as explained in PRX and ET fuze.

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4.5 LIMITATIONS OF ELECTRONIC FUZE • The electronic circuits though adds many valuable features to the fuze, but these additional feature comes at the cost of complex design and susceptibility of electronic fuze to some environmental and working conditions. Few limitations of electronic fuze are described below

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4.5 LIMITATIONS OF ELECTRONIC FUZE •

•

susceptibility to electromagnetic interference (EMI): this problem becomes more severe in case of proximity fuzes as it can lead to wrong target sensing and hence making the fuze to function before it actually reaches in the vicinity of target (Ii) possibility of jamming: the proximity fuzes are susceptible to jamming. If enemy knows the technical specifications (e.G. Operating frequency etc.), He can easily misguide the fuze. Using appropriate modulation and coding schemes can solve this problem. CONTENTS

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4.5 LIMITATIONS OF ELECTRONIC FUZE (iii) additional reliability constraints due to integration of electronic circuits in to the fuze. (iv) fuze design becomes more complex due to integration of electronic circuitry and its interfacing with mechanical sub-systems.

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4.6 Closure • The electronic fuzes were developed in mid 1960’s and there after there have been continuous development in this technology. Today, electronic fuzes are being used in many modern weapon systems and have replaced mechanical fuzes from many of their applications. Basic elements of electronic fuzes, types of electronic fuzes and their working principle, advantage and limitations were discussed in this chapter. Whatever is the type of fuze, testing of fuze is very important to ensure its satisfactory performance. Testing of fuzes in discussed in the next chapter. CONTENTS

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CHAPTER 5 TESTING OF FUZES 5.1 Introduction • As discussed in the previous chapters, fuze is the brain of the ammunition and controls its safety and firing. Malfunctioning of fuze can lead to major accidents resulting not only in the loss of man and money, but also of the morale of the armed forces. This necessitates stringent controls and tests during the development of the fuze, its acceptance for mass production, during manufacturing and after manufacturing. CONTENTS

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5.1 Introduction • The basic question is “Does the fuze satisfies all its requirement?” The tests are standardized and are mandatory to perform before the fuze is cleared for use. Most of the tests are listed in the military standards (MIL-STB-331B) laid down by Department of Defence, U.S.A. and are discussed in detail in Appendix B. • Fuze tests can be classified as Component tests, Safety tests, Surveillance tests, Proof tests etc. These are discussed in detail below. CONTENTS

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5.2 Development and Acceptance Tests • Development tests are performed to evaluate the fuze design concepts i.e. to access whether the principles involved in the fuze can lead to an improved design or the concept needs to be modified or discarded. Acceptance tests are performed to evaluate the final design and are also called approval tests or evaluation tests. CONTENTS

217

5.2 Development and Acceptance Tests • Development tests are designer specified tests, carried out for individual components, subassemblies and entire fuze. These tests are more severe and more precise because this gives the designer as idea about the extent to which the design can be improved • Acceptance tests are specified by some inspection agency or user. They are carried out only for final fuze assemblies. These tests are usually less severe and less demanding than the development tests CONTENTS

218

5.3 Component Tests: • These tests are carried out to access the safety, reliability and performance characteristics of individual elements. These tests are divided into three main groups as discussed below

CONTENTS

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5.3 Component Tests: 5.3.1 Tests for Explosive Elements • Explosive elements are tested singularly or in combination with other elements of the train. Important characteristics recorded are input, output and train continuity. Input is measured by actually detonating primers and detonators by mechanical forces or electrical stimulus and recording the input energy required for the purpose. CONTENTS

220

5.3 Component Tests: • To measure the output of the detonator, it is detonated against sand, lead or steel and the deformation caused in the sand, lead or steel gives the magnitude of output energy of the detonator. Continuity of the explosive train is checked by assembling the whole train and measuring the output of the train for given input. Static Detonator Safety Test is also carried out to check whether the rest of the train will be set off when the detonator is initiated in initial unarmed state. CONTENTS

221

5.3 Component Tests: 5.3.2 Tests for Mechanical Devices: • These tests are used to test the rigidity, strength and performance of mechanical components of fuzes when they are subjected to extreme centrifugal forces and setback forces after launch. These forces are simulated for test conditions by centrifuges, spin machines, air guns and other devices. CONTENTS

222

5.3 Component Tests: • . Centrifuge is used to simulate the centrifugal force experienced by the fuze. Spin machines are used to simulate the spinning of fuze in flight. Setback force may be simulated by drop tests or air gun. Shock tests are performed to test mechanical components when subjected to high accelerations and retardations CONTENTS

223

5.3 Component Tests: 5.3.3 Tests for Power Sources: • These tests are performed only occasionally to access the performance of power source in the fuze. If the power source is spring or a rotor, it is tested like other mechanical devices. If the power source is electrical, it is tested as breadboard models in conventional ways. It is to establish that the power source can set off the primer or detonator in the particular fuze. CONTENTS

224

5.4 Proof Tests: 5.4 Proof Tests: • The basic concept of the proof testing is to ensure that the fuze is tested at all conditions similar to those under which it is expected to perform. This is the only mean of evaluating final assembly operations and possible effects of combined forces that were not apparent for individual elements CONTENTS

225

5.4 Proof Tests: • CQA has laid down instructions for proof testing of fuzes. The test usually is carried in two stages. First, a static test is carried out in which fuze is fired by mechanical means (dropping of weights) without actually firing the ammunition and the results are noted to see the performance of explosive train and safety devices in the fuzes. The second stage is the firing of actual ammunition through the gun with fuze attached to it. The ammunition used may be an empty shell or a filled one. CONTENTS

226

5.5 Safety Tests: 5.5 Safety Tests: • These tests are designed to investigate the safety requirements of the fuze during handling, transportation etc. These tests are classified as destructive and non-destructive tests.

CONTENTS

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5.5 Safety Tests: 5.5.1 Destructive Testing: • In these tests, the operability of the fuze is not required and is used to validate the design or a lot of fuze. These tests check the ruggedness of a fuze and sensitivity of the explosive elements when subjected to severe impacts. These tests include 12 m drop test, jolt test, jumble test etc and are discussed in detail in Appendix B. CONTENTS

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5.5 Safety Tests: 5.5.2 Non-Destructive Testing: • In these tests, operability is required. These tests check the sensitivity of explosive elements when subjected to minor impacts and loads. These tests include parachute drop test, transportation and vibration tests etc. CONTENTS

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5.6 Surveillance Tests: 5.6 Surveillance Tests: • These are the routine checks carried out for ammunition, fuzes and explosives in movement, storage and use to investigate the degree of serviceability and rate of deterioration. These checks are usually conducted at an interval of 6 months or a year. CONTENTS

230

5.6 Surveillance Tests: • The deterioration of fuze during storage may be due to corrosive atmosphere, extreme temperatures, moisture, corrosion of metallic components, chemical decay of explosive components with time or any other similar reason. Many of these problems can be avoided by using hermetically sealed cans for storage of fuzes or by using moisture-proof protective coatings. CONTENTS

231

5.6 Surveillance Tests: 5.6.1 Accelerated Environment Tests: • During the development stage of the fuze, it is not possible for designer to foresee the effects of storage and environmental variables on fuze with time as long-term tests cannot be tolerated during the development stage. CONTENTS

232

5.6 Surveillance Tests: • To solve this problem, the fuzes are tested in severe environments for short periods to simulate the effect of milder environments over extended periods. Such test are thus accelerated and termed as Accelerated Environment Tests. Some of these tests are fog test, extreme temperature storage test, vacuum-steam-pressure test, waterproofness test, rain exposure test etc. CONTENTS

233

5.7 Testing of Electronic fuzes 5.7 Testing of Electronic fuzes • The electronic circuits integrated in the electronic fuze are required to be tested for their functionality and reliability. The testing includes testing of component, functional testing of fuze system and calculation of performance parameters. The parameters obtained are compared with the desired parameters. During development stage, the designers subject the fuze components and complete fuze to certain specific tests to meet the operational requirements. CONTENTS

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5.7 Testing of Electronic fuzes • When the fuze is productionised, test procedures commensurate with the test carried out during the design stage. The complete fuze system can be tested for all the performance parameters only when designer has designed the system with its testability in mind. The concept of design for testability is discussed hereunder CONTENTS

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5.7 Testing of Electronic fuzes 5.7.1 Design for testability Concept: The concept of testing starts at the design stage of a product and electronic fuze is not an exception. The ultimate aim of any design is to convert it into a functional product. The complete design is functionally divided into various blocks and each block is assigned a specific function. The functional division of full design not only helps the designer to complete his design easily, it also helps him to test his design after completion. CONTENTS

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5.7 Testing of Electronic fuzes • Various test points are provided in between at the output of each block to verify the output of each block. The debugging of design becomes easier as designer now can pin point the defected block and rectify the problem. Same idea applies in case of testing of the design when it is physically implemented on the PCB. The test points helps in testing of individual block. CONTENTS

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5.7 Testing of Electronic fuzes • For example, consider the system represented in the Figure 5.1. The system has certain function to perform and it is functionally divided into four modules, Module 1 to Module 4. System has a single primary input and single primary output. Each module performs a specific function and passes on the output to the next module. Designer knows the output of each module. CONTENTS

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5.7 Testing of Electronic fuzes • The T1 to T3 are the test points provided by the designer to make system testing and debugging easy. By providing T1-T3 each module of the system can be tested and if any problem occurs the corresponding module can be corrected. To test the intermediate modules, Module 2 and 3, the primary input is set such that it gives the desired output at module 1 to set the input of intermediate modules CONTENTS

239

5.7 Testing of Electronic fuzes

Figure5.1: A hypothetical system CONTENTS

240

5.7 Testing of Electronic fuzes • Similarly, in case of electronic fuze, the test points are provided to test Proximity sensor, Time delay unit, safety circuit etc. However, depending on the type of fuze i.e. whether it is Proximity (PRX) or Electronic Time (ET) or Electronic Point Detonation (EPD) or Multi-Option Fuze (MOF), the functional verification test setup will differ. CONTENTS

241

5.7 Testing of Electronic fuzes • The failure of any of the electronic component can lead to the functional failure of the fuze in its operation and hence it is extremely important to test the electronic components before use and after mounting them on PCB & verifying the functionality of circuit in various conditions. CONTENTS

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5.7 Testing of Electronic fuzes • First of all the screening of electronic components is done, then PCB level testing of circuits is performed, and then finally complete fuze assembly is tested. The design parameters of the fuze dictate the type of test to be specified at various stages of development and manufacture. These tests form an integral part of fuze development and production programme. • Screening of components before use and testing of various basic circuits, which constitute the electronic assembly of fuze, is discussed in following.

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5.7 Testing of Electronic fuzes 5.7.2 Screening of electronic components: The electronic components should be subject to screening before taking the lot for use. The basic screening procedures adapted are a) ‘g’ Test. b) High temperature storage, c) Temperature Cycling, and d) Power burn in (24 Hrs). CONTENTS

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5.7 Testing of Electronic fuzes • A fix % (1 or 2 %) of components are subjected to a force of some specified amount (e.g. 20,000 g, actual force required to be applied for testing depends on the conditions in which the fuze is going to work such as acceleration force, air flow, spin force etc.) for one minute. If 1% of the tested components changes beyond the limits value the whole lot to be rejected. CONTENTS

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5.7 Testing of Electronic fuzes • The passive components (Resistors, Capacitors and Inductors) are subject to high temperature storage of 100° C for 48 Hrs and temperature cycling of extreme temperature for 5 cycles. One cycle is 30 minutes long with 5 to 15 minutes recovery time. Capacitors are subjected to power burn in for 100 Hrs at +85°C at rated voltages. The active components (Transistors) are subject to power burn in for 24 Hrs at room temperature and temperature cycling of -55°C to +125°C for 5 cycles. • Based on the screening results the lots are selected/rejected. The selected components are then utilized for making PCBs to implement the required circuits. CONTENTS

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5.7 Testing of Electronic fuzes 5.7.3 PCB level testing of electronic fuze: After making the PCBs, the respective electronic circuits should be tested for their functionality and performance. The PCBs are first checked for the manufacturing defects and then they are subjected to performance evaluation tests. The manufacturing defects are inspected by visual inspection. The following points are ensured by visual inspection of PCBs CONTENTS

247

5.7 Testing of Electronic fuzes i)

The components of proper value are cleaned, tinned, sleeved and mounted at the correct position. ii) There are no dry solders iii) Assembly is clean and free from flux and dirt. iv) The joints are proper and there are no short circuit or open circuit defects CONTENTS

248

5.7 Testing of Electronic fuzes • After visual inspection, the performance of respective circuits is evaluated by specified testing methods. The testing requirement and performance parameters of some of the fundamental circuits of electronic fuze are discussed below. i) Oscillator Circuit: The frequency output of the oscillator is verified with the help of frequency counter. The oscillator circuit is checked for amplitude of output voltage at its load and the frequency of oscillations. Digital multimeter or oscilloscope may be used to measure the amplitude of output voltage. CONTENTS

249

5.7 Testing of Electronic fuzes • The amplitude of output voltage should be with in the specified limits and out put frequency should be in specified range. The signal strength of transmitted signal is measured with help of signal strength meter by tuning the signal strength meter to the corresponding reading of frequency counter. The signal strength (measured in DB) should be above minimum specified value at specified distance or height. The same data converted to mV gives the sensitivity of oscillator circuit, which is the sensitivity while receiving the return signal from target.

CONTENTS

250

5.7 Testing of Electronic fuzes • a)

Audio Amplifier circuit: The assembled audio amplifier circuit is subject to the following tests. Delay time test: This test is carried out to check the delay time between the switching ON and the appearance of voltage at the trigger output of the circuit. The delay time is measured with the help of counter

CONTENTS

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5.7 Testing of Electronic fuzes • (b) Amplifier threshold: The threshold input voltage of an amplifier is defined as the minimum voltage which is required to generate an output pulse (trigger pulse) of required amplitude. An audio signal is applied at input and increased slowly until a signal of desired strength appears at output. CONTENTS

252

5.7 Testing of Electronic fuzes • The minimum corresponding input voltage is noted down, and is referred to as amplifier threshold voltage. It should be between specified limits. A low frequency signal generator (sine wave), regulated DC power supply, digital multi-meter and oscilloscope (CRO) are required to perform this test CONTENTS

253

5.7 Testing of Electronic fuzes (c) Amplifier bandwidth: Bandwidth of an amplifier is defied as the range of frequencies for which amplifier gain falls 3 DB of mid-frequency gain value i.e. range of frequencies which can be processed (amplified) by the amplifier satisfactorily without any distortion. The amplifier is given an input signal from oscillator, which is varied from minimum frequency to maximum frequency, and correspondingly the output at amplifier is measured. The corresponding minimum (Low) frequency and maximum (High) frequency for which amplifier gain falls below 3 DB are noted down. This range of frequencies from low frequency to high frequency gives amplifiers bandwidth. CONTENTS

254

5.7 Testing of Electronic fuzes (d) Dynamic range: Dynamic range indicates that for a specified signal-to-noise ratio (SNR) there is no distortion in the output signal for any increase in input signal up to the dynamic range of amplifier. The noise in no signal condition is measured at output, and then an input signal, which increases output by, required SNR is applied and noted down. Now increase the input signal slowly. The dynamic range is the range of input signal for which there is no distortion in output signal. CONTENTS

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5.7 Testing of Electronic fuzes (e) Output Pulse (trigger pulse): The amplitude of the output voltage pulse should be greater than or equal to the specified value. It is measured with the help of an oscilloscope. (f) Amplifier noise: The thermal noise level at output of amplifier for a specified value of load resistor should be below specified limit. This is measured with the help of oscilloscope or milivoltmeter/micro-voltmeter CONTENTS

256

5.7 Testing of Electronic fuzes (iii) Electronic Timer / Delay circuit: The timer circuit testing depends on the design parameters of the circuit. Common tests performed on timer circuits are, test of frequency of clock generating oscillator, time data retention test, preset time test, and time set reset test. To set the fuze in various testing modes, a ‘Fuze Programmer Unit’ is provided by the designer. CONTENTS

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5.7 Testing of Electronic fuzes • The clock-generating oscillator is usually ‘power on oscillator’, which starts generating clock wave as soon as it gets power input. The frequency of oscillations can be checked with the help of oscilloscope. The frequency of oscillations should not very with fluctuation in supply voltage, for a specified range of supply voltage. The time data retention test is done to check whether the time data set in ET fuze remains in its memory for the specified time. CONTENTS

258

5.7 Testing of Electronic fuzes • The preset time test is done to verify that timer provides the delay precisely equal to the set time ± Accuracy. The timer is set for some time delay value and output terminals are checked, the trigger pulse should appear at the output terminals precisely after set time ± Accuracy. The time set reset test is done to verify that timer is re-settable i.e. if by mistake if any wrong value has been fed it can be corrected and fresh data can be fed to set the operation time. CONTENTS

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5.7 Testing of Electronic fuzes • Some ET fuze also have switches (such as floating switch) which enable the clock input of timer, in such fuzes the switches are left open and timers are set for some value and output is checked, there should be no output if switch is open, this test is called ‘safety test’ of timer CONTENTS

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5.7 Testing of Electronic fuzes • (iv) Electronic firing circuit: The firing circuit is tested for the amplitude and duration of the firing pulse. Oscilloscope can be used to check the amplitude of the firing pulse. • (v) Power supply: The battery is tested for no load output voltage and full load output voltage. The voltage droop of output voltage should be within specified range. CONTENTS

261

5.7 Testing of Electronic fuzes • Multi-meter along with resistance of suitable value can be used to perform this test. This is very important that the output voltage of battery remains constant at its specified value. If the output voltage falls with time and voltage droop is high, the performance of the other circuits is adversely affected and fuze may not function accurately. CONTENTS

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5.7 Testing of Electronic fuzes 5.7.4 Equipments for Screening: • Following equipments/facilities are required to perform screening of electronic devices. iii) ‘g’ test: spinning machine of 40000 g, iv) Power burn chamber, v) High temperature storage chamber, vi) Low temperature storage chamber, vii) Spin test: spinning M/C for sub assembly & assembled fuze with low rpm. viii) Curve Tracers CONTENTS

263

5.7 Testing of Electronic fuzes 5.7.5 Equipments required for PCB level testing: Following test equipments are required to perform the PCB level testing of electronic fuzes. i) Oscilloscope / digital RF oscilloscope, ii) Regulated DC power supply, iii) Multi-meter, iv) Universal time and frequency counter, v) Fuze setter / Time setter, vi) True RMS meter, vii) Sine and square wave generator, viii) Signal strength meter, CONTENTS

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5.7 Testing of Electronic fuzes ix) LCR meter, x) Low distortion signal generator, xi) Filter circuits, xii) Fuze programmer unit (specific for a fuze). xiii) Spectrum Analyzer xiv) GP receiver. CONTENTS

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5.8 Closure • The performance of ammunition is directly related to the performance of fuze. This necessitates extensive testing and proofs of the fuze before it can be used with the ammunitions. Testing of the fuze has been designed to assess the performance of fuze in extreme conditions by simplified tests and procedures. CONTENTS

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CHAPTER 6 NEW TRENDS IN FUZE TECHNOLOGY 6.1 Introduction • The innovations in fuzing technology go parallel with the advancement in electronics industry. The discovery of transistor was a break-through in electronics and since than, there have been continuous development in this field. The first fully transistorized fuze M429 was made in the 1965-1970 time period for a 2.75″ rocket to use in Vietnam War. There after electronic fuzes were made using integrated circuit technology and proximity fuze and electronic time fuze were developed.

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6.1 Introduction • The miniaturization in electronics continued and hence increasingly complex systems were made in even smaller chip area. The electronic technology evolved from Small Scale Integration (SSI) stage, where in only few components could be integrated in a chip to Very Large Scale Integration (VLSI), where millions of components can be integrated in a single chip. The use of Integrated Circuit (IC) technology gives fuze designer more space to integrate more circuits and include additional features. CONTENTS

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6.1 Introduction • The modern programmable Proximity (PRX) and Programmable Electronic Time (ET) fuzes are examples of this. Now a days we have MultiOption Fuze (MOF), which represents the latest development in electronic fuze technology. In the following sections, we will discuss the latest developments in fuzing technology, latest products and future development programme. CONTENTS

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6.2 Latest electronic fuzes from leading manufacturers • The latest electronic fuzes from leading manufacturers are discussed in the following i) Junghans Feinwerktechnik, Germany has developed a new series of Digital fuzes. The Multi Option Fuzes for Artillery (MOFA) DM74 and DM84 as well as the Electronic Time Fuzes DM52A1 and DM52A2 represent the latest generation in fuze know-how. CONTENTS

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6.2 Latest electronic fuzes from leading manufacturers • These fuzes have been designed to utilize the principle of digitization, inductive programming by direct communication with automatic fire control loading systems of all modern howitzers. The optronic Mortar Proximity Fuze PX581 is independent of caliber and can be mounted on 60 mm, 81 mm and 120 mm shells without adjustments. Its optronic capabilities will allow no interference by electronic counter measures like for instance "Shortstop". CONTENTS

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6.2 Latest electronic fuzes from leading manufacturers • Due to its special technology, the fuze functions highly precise at low ground distances and thus provides an optimal ammunition result. The DM581 is latest optronic proximity fuze and is superior to conventional proximity fuzes, used in today's armed forces. It utilizes advanced laserbased distance measurement technology for target recognition. The optical fuze transmitter sends out light pulses at the rate of 500 pulses per second while the receiver constantly measures the distance from the target. CONTENTS

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6.2 Latest electronic fuzes from leading manufacturers •

The intelligent decision-making logic recognizes the target and detonates the shell at the programmed altitude and at the desired moment. The fuze recognizes the ground surface but does not react to clouds, mist, snow or rain. Due to its very sophisticated optro-electronic measuring principle, it is not possible to interfere with any known counter methods. CONTENTS

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6.2 Latest electronic fuzes from leading manufacturers ii) FUCHs Electronics, South Africa has developed a new Multi-Option Artillery Fuze M9801. The M9801 multi-option fuze, has four functioning modes including – Point Detonating Super Quick (PDSQ), Point Detonating Delay (10 – 100 ms, settable), Proximity (4m/ 8m/ 12-50m height of burst, settable) and time (3 – 199.9 seconds, settable). CONTENTS

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6.2 Latest electronic fuzes from leading manufacturers •

To defeat jammers, the timer is also used to inhibit the proximity function until the projectile is overhead its target. Another new fuze variant compatible with the M15A2 (Inductive Fuze setter) is M9804 ET fuze, which stores time data in an integral non-volatile memory, the last entry being retained indefinitely until the fuze is reprogrammed. CONTENTS

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6.2 Latest electronic fuzes from leading manufacturers • FUCHs Electronics RO68 proximity fuze operates in UHF frequency range and employs a specialized Doppler technique to accurately sense the detonation distance above the ground. The fuze employs frequency agility to provide the fuze with an effective immunity to combat enemy countermeasures CONTENTS

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6.2 Latest electronic fuzes from leading manufacturers (iii) RESHEF Technologies, Israel KAPPA M175 is described as the next generation fuze. KAPPA M175 is a radio-operated proximity fuze, based on a frequency modulated continuous wave radar sensor, which detonates the carrier rocket warhead at an optimum height. CONTENTS

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6.2 Latest electronic fuzes from leading manufacturers (iv) Netherland’s Signal Usfa and TNO Physics & Electronics Laboratory have developed a new generation proximity fuze for the Netherlands armed forces. It is known as– Multi-role Extended range Digital Electronic Artillery (MEDEA) Fuze. Its functionality includes – impact, delayed impact, proximity to land, sea and air targets and programmed time detonation. The fuze will be useful in ordnance ranging between 76-155mm caliber CONTENTS

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6.2 Latest electronic fuzes from leading manufacturers (v) Alliant Tech System’s XM773 MultiOption Fuze (MOFA) incorporates many distinguished features. The fuze combines the proximity, time, super quick and delay modes of functioning and it is both hand and inductively settable. The fuze characteristics include a liquid crystal display providing a clear visual indication of the setting. CONTENTS

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6.2 Latest electronic fuzes from leading manufacturers • Alliant Tech Systems is presently instrumental in development of next generation Electronic Time Fuze for Mortar (ETFM). The plan is to develop mortar electronic time fuzes XM784 and XM785 to replace the mechanical time fuzes (M776& M772) currently employed by the US Army on the 60 mm, 81mm and 120 mm white light & IR illumination rounds, and the 81 mm smoke round. CONTENTS

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6.2 Latest electronic fuzes from leading manufacturers CONTENTS

Figure 6.1: ETFM XM 784 and XM 785 CONTENTS

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(vi) BT Fuze Product’s M234/M235/M236 are new Self Destruct (SD) fuzes. SD fuzes reduce the number of hazardous DPICM Grenade dud submunitions on the Battlefield

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6.2 Latest electronic fuzes from leading manufacturers Their advantages include enabled maneuverability, reduced clean- up efforts, addressed humanitarian issues etc. The following figure describes the SD fuze operation, 1 indicates the fuze before operation and 2 indicates after operation Figure 6.2: SD Fuze operation. CONTENTS

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6.3 Innovations in Proximity Fuzing • The proximity sensor is the main module of proximity fuze. In the following paragraphs, the latest developments in proximity sensing methods are discussed • FM / CW Ranging Systems: The FM / CW Ranging Systems offers discriminate frequency information instead of amplitude information and hence are more immune to enemy counter effects such as jamming etc. The use of FM / CW Ranging Systems in proximity fuzes also provides increased accuracy of Height- of- Burst (HOB). CONTENTS

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6.3 Innovations in Proximity Fuzing • Dual Channel Directional Doppler Ranging (DDR) Signal Processor: This system helps the fuze to discriminate between approaching and receding Doppler and provides noise immunity From Internal or External Sources. The DDR signal processors are highly integrated and single chip signal processor solution CONTENTS

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6.3 Innovations in Proximity Fuzing • Electrostatic Proximity sensor (EPS) concept: EPS utilizes the accumulated charge (which is accumulated by the target by frictional charging currents and combustion charging currents) of the target to detect it and give the firing command to the fuze. EPS detects E- field surrounding target charge. This type of sensors will be very • useful in proximity fuze used in ground to air and air-to-air ammunitions. CONTENTS

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6.3 Innovations in Proximity Fuzing • The Guidance Integrated Fuze (GIF) / Course Correcting Fuze (CCF) are considered as smart fuzes which enhance the effectiveness of the artillery systems. GIF provide “first round – steel on target” kind of effectiveness. GIF corrects the ballistic trajectory in 2D, resulting in a small terminal miss distance CONTENTS

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6.4 Innovations in fuze manufacture technology and safety mechanisms: • In electronic fuze industry, emphasis is being given to modular approach of fuze design. The module is defined as a functional unit of a system. In modular approach, the modules are designed such that one module fits into many fuze housings and is compatible with other fuzes. This approach offers the advantage of having flexibility in fuze manufacturing, testing based on GO/NO-GO, high component density, and also reduces the cost of production. The Alliant Techsystems XM784 and XM785 are the example of this technology. CONTENTS

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Figure 6.3: Example of modular approach to fuze design CONTENTS

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6.4 Innovations in fuze manufacture technology and safety mechanisms: • The use of cost effective COTS technology offers advantages which includes, use of 2Layered Stiffened Flex Printed Wiring Board (PWB). In 2-Layered Stiffened Flex PWB on topside components are mounted and on backside stiffener is applied. This minimizes the interconnects and make the PWB easy to package. CONTENTS

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6.4 Innovations in fuze manufacture technology and safety mechanisms: • Using Surface Mount Devices (SMDs) helps in automating the production line and minimizing the PWB size. Standard pickand-place/re-flow solder machines can be used for this purpose. An example of this technique is described in figure 6.4.

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Figure 6.4: COTS and SMD technology CONTENTS

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6.4 Innovations in fuze manufacture technology and safety mechanisms: • The use of Dual Microprocessor technology is also becoming the need for today in fuze safety. Two microprocessors are used, one for commanding fuze operation and other dedicated to safety only. The hand settable fuze and LCD display on fuze makes the fuzes more user friendly. The Alliant Techsystems latest ETFM includes this feature. The block diagram circuit of the ETFM fuze is described in figure 6.5. CONTENTS

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Figure 6.5: Dual micro controller for safety

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6.5 Future of Fuze technology Futuristic Fuze technologies aims at making which are • Smaller, • Smarter, and • Common modular components • The futuristic trends in fuze development will be concentrated on miniaturization and use of high density ICs and digital logic circuits into electronic fuzes. CONTENTS

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6.5 Future of Fuze technology • The electronic industry has moved into the era of VLSI (Very Large Scale Integration), which contains millions of electronic components on a single chip. The concept of System On Chip (SOC) has also induced in fuze technology from VLSI technology. The integration of digital logic circuit adds intelligence to the fuze and makes it smarter for use in modern smart weapon systems. • The evolving fuze technology requirements can be summarized as follows CONTENTS

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6.5 Future of Fuze technology • Scaleable effects with multi-mode and multipurpose functionality. • Fuze on a chip. • Precision explosive trains and detonators. • MEMS (Micro Electro-Mechanical System), lower cost & better reliability. • Power sources, primary and reserve. • Guidance integrated fuze (GIF) / Course Correcting Fuze (CCF). CONTENTS

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6.5 Future of Fuze technology The solution to above requirements lies in the following. • Use of Ultra-miniature components. • Cost Reduction via Multi-component modules, FPGA, DSP and MEMS. • Batteries - power delivery & shelf life. • Novel techniques for S&A, timing precision. • Performance against unusual targets, stealth & multilevel bunker. • Precision range sensing for delivery of non-lethal munitions CONTENTS

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6.6 Closure • In summary, it can said that enhanced capabilities are required to meet modern and future threats and increased levels of integration will be required in future munitions and weapons. Fuzing applications are expanding beyond traditional techniques CONTENTS

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BIBLIOGRAPHY 1 2 3 4 5

“Engineering Design Handbook: Ammunition Series, Fuzes”, U.S. Department of Commerce, National Technical Information Service. “Ammunition Maintenance Instructions for Army ordnance services FZ-Series”, Fuzes and Gaines, AMI FZ/23, First Issue, Proximity Fuzes (V.T.), Chief Supdr of Dev., T.D.E. (ammn.), Kirkee. “Ammunition Maintenance Instructions”, AI / Series-Advance Information, A1/84/5 Fuzes for 155mm Ammunition, CQA (Ammn.), Khadki, Pune-3. “Proximity Fuze – testing and evaluation”, B. S. Kulkarni, Proceedings of National Seminar on Timers and Fuzes, 4-5 February, 1983, PXE, Chandipur. “Time – Proximity Fuze”, Major G.S. Saund, Proceedings of National Seminar on timers and fuzes, 4-5 February, 1983, PXE, Chandipur. BACK

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BIBLIOGRAPHY 6 7 8 9 10

“Proximity Fuzes”, Harner Selvidge, Electronics, February 1946. “The evolution of the US Army Artillery Fuzes to the Electronic Age”, J. F. Springer, Military Technology, Vol. 30, No. 12, Dec. 1989, pp 77-88. “South African Fuze Systems Detailed”, Janes Defence Weekly, Vol 21, No. 5, 1994, pp 19. “Modular Approach to a Proximity Fuze”, G.C. Dubey, Technical report No. SPL-29/73, Solid State Physics lab, DRDO, New Delhi. “Radio Proximity Fuzes”, John W. Lyons, E. A. Brown and B. Fonoroff (ret.), Army Research Laboratory, U.S.A. BACK

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BIBLIOGRAPHY 11

12

"Development of Proximity Fuzes (VT) for Projectiles VT Fuzes MKS 32 to 60, Inclusive (General Description)." N.E. Dilley, Chapter 1 of The World War II Proximity Fuze: A Compilation of Naval Ordnance Reports by the Johns Hopkins University Applied Physics Laboratory. (Silver Spring MD: The Laboratory, 1950): 1-12. [Declassified 16 Jun. 1976]. MIL – STD 331 B, Military Standard for fuze and fuze components environmental and performance tests, AMSC, N/A, Department of Defence, USA.

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Website Reffered: • • • • • • •

W.1 W.2 W.3 W.4 W.5 W.6 W.7

http://www.atk.com. http://www.arcus-bg.com. http://www.btfuze.tw.l-3com.com. http://www.fuchs.co.za. http://www.hblnife.com. http://www.junghans-fwt.de. http://Israel.motorola.com/ged. BACK

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Website Reffered: • • • • • • •

W.8 http://www.patria.fi. W.9 http://w4.pica.army.mil/PicatinnyPublic/index.asp. W.10 http://www.resheffuzes.com W.11 http://www.army-technology.com W.12 http://www.globalsecurity.org W.13 http://www.global-defence.com W.14 http://www.dtic.mil/ndia BACK

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Further Reading: • F.1 “Antenna and wave propagation”, K. D. Prashad, Satya Prakashan, New Delhi. • F.2 “Antennas”, John D Kraus, Tata Mc Graw Hill Publications, New Delhi. • F.3 “Electronic Communication Systems”, George Kennedy, Glenceo/ McGraw Hill, Publications, NY, U.S. • F.4 “Communication Systems”, Simon Haykins, Prentice Hall Inc. Publications, Upper Saddle, NJ, USA. • F.5 “Integrated Electronics”, J. Millman and C. C. Halkias, Tata Mc Graw Hill Publications, New Delhi. • F.6 “Microelectronic Circuits”, S. Sedra and K.C. Smith, Oxford University Press Publications, U.K. • F.7 “Digital Design Principles and Practices” John F. Wakerly, Prentice-Hall, Inc. Publications, Upper Saddle, NJ, USA. BACK

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APPENDIX – A MIL-STD-331B • Different Fuze designing and developing agencies follow different standards for fuze testing. One of the most widely accepted testing standards for fuze testing is the compilation by Department of Defence, U.S.A. and is referred to as MIL-STD331B, which was released on 1st December, 1989. This standard described the tests to be carried out to determine the safety, reliability and performance characteristic of weapon system and fuze component at any stage of their life. BACK

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APPENDIX – A MIL-STD-331B • This standard generally applies to all fuzes as well as components of weapon system serving a fuze function. The standard contains tests to be carried out, equipment to be used and the range of data to be satisfied by the fuze for passing the test. • MIL-STD-331B standards classify the tests into six categories. These categories and the tests carried under them are discussed briefly below. For detailed discussion, one can refer to the standard referred above. BACK

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Group A – Mechanical Shock Tests •

In these tests, fuzes are subjected to single or repeated impacts, which generally simulate possible mishandling during the logistical or operation cycles. a) Test A1 – Jolt: • This is a laboratory test simulating ground transport conditions. The fuze must withstand a series of impacts applied in a controlled direction and amplitude. BACK

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Group A – Mechanical Shock Tests b) Test A2 – Jumble: • This is also a laboratory test simulating ground transport conditions. The fuze must withstand random impacts imparted by a free-fall inside a rotating wood-lined box. c) Test A3 – 12 meter (40 foot) Drop: • This is a laboratory or field safety test simulating mishandling during loading and unloading of ammunition in ships. The fuze must withstand a 12 meter (40 ft) free-fall drop onto a steel plate. BACK

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Group A – Mechanical Shock Tests d) •

e) •

Test A4 – 1.5 meter (5 foot) Drop: This is a laboratory safety and reliability test simulating handling and tactical conditions. Separate fuzes or fuzes attached with ammunition are dropped from 1.5 m (5 ft) onto a steel plate. Test A5 – Transportation Handling (Packaged Fuzes): This is also a laboratory safety and reliability test simulating handling conditions. Packed fuzes or fuzed ammunition are preconditioned to specified temperature and subjected to controlled drops, roll-overs and impacts. BACK

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Group B – Vibration Tests `Fuzes are subjected to vibrations of specified frequency, amplitude and duration, simulating conditions anticipated during transport or tactical use. a) Test B1 – Transportation Vibration (Bare Fuzes): • This is a laboratory safety and reliability test simulating transportation conditions. Bare • fuzes or fuzed ammunition are preconditioned to specified temperature and vibrated on a schedule of controlled frequencies and amplitude. b) Test B2 - Transportation Vibration (Packaged Fuzes): • This test is similar to Test B1 except that packaged fuzes are used in this test as against bare fuzes of the previous test. c) Test B3 – Tactical Vibration: • This test is also similar to Test B1 and is used to simulate tactical conditions. BACK

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Group C – Climatic Test • a) • b) •

In these tests, fuzes are subjected to realistic extreme climatic conditions for specified period to simulate storage and exposure of similar conditions during the life of the fuze. Test C1 – Temperature and Humidity: This is a laboratory safety and reliability test simulating storage conditions. The fuze must withstand exposure to repeated cycles of extreme temperature and humidity. Test C2 – Vacuum-Steam-Pressure: This is a laboratory safety and reliability test simulating storage or ready use conditions. The fuze must withstand exposure to a series of 15-minute vacuum-steam-pressure cycle.

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Group C – Climatic Test C Test C3 – Salt Fog: • This is a laboratory safety and reliability test simulating bare fuze exposure to a moist and salty atmosphere. d) Test C4 – Waterproofness: • This is a laboratory safety and reliability test, which subjects the fuze to submersion in water. The fuze must remain leak-free when submerged to a depth of 10.7 m (35 ft) of water. BACK

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Group C – Climatic Test e) Test C5 - Fungus: • This is a laboratory safety and reliability test simulating adverse storage condition. The fuze must withstand the growth of fungus growth. f) Test C6 – Extreme Temperature: • This is also a laboratory safety and reliability test simulating extreme storage conditions. The fuze must withstand continuous exposure to extreme low and high temperatures. BACK

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Group C – Climatic Test g) Test C7 – Thermal Shock: • This test is similar to Test C6. The fuze must withstand sudden transition in extreme low and high temperatures. h) Test C8 - Leak Detection: • This is a laboratory performance test to measure the fuze leak rate. Fuzes must exhibit a rate of leakage of a tracer gas or air below the specified limit. BACK

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Group C – Climatic Test i) •

j) •

Test C9 – Dust: This is a laboratory safety and reliability test simulating adverse storage, handling, transportation and tactical conditions. The fuze must function properly after exposure to a dusty environment. Test C10 - Solar Radiation: This is a laboratory safety and reliability test to determine the effects of solar radiation on packaged or unpackaged fuzes or fuzed ammunitions that may be exposed to sunshine during operation or unsheltered storage. BACK

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Group D – Safety, Arming and Functioning Tests a) •

b) •

These tests measure the performance characteristics of the fuze such as explosive safety, arming distance or time, output etc. Test D1 – Primary Explosive Components Safety: This is a laboratory safety test simulating inadvertent initiation of the fuze primary explosive. Explosive component beyond the explosive train interrupter must not be initiated nor should fuze produce a hazardous release. Test D2 – Projectile Fuze Arming Distance: This is a field performance test used to determine the no-arm, meanarm and all-arm distances for impact detonating projectile fuzes. An optional field safety test is included which determines whether the fuze is armed at the muzzle of the gun.

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Group D – Safety, Arming and Functioning Tests c) • d) • e) •

Test D3 – Time to Air Burst: This is a field performance test used to determine functional accuracy of mechanical and electronic projectile time fuzes. Test D4 - Explosive Component Output: This is a laboratory performance test used to determine explosive component output, performance uniformity and suitability for a particular design application. Test D5 – Rain Impact This is a safety and performance test used during fuze development to demonstrate that the impact sensing element will not function as a result of traversing a specified rain environment and will then function reliably on impact with the test target.

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Group E – Aircraft Munition Tests a) •

b) •

Fuzes associated with airborne ammunitions are subjected to impacts or forces which might be encountered in takeoff and landing or accidental separation of the ammunition from the aircraft. Test E1 – Jettison: This is a field safety test for fuzes with flight-selectable safe jettison capacity. When the fuze is jettisoning safe, the fuze must not contribute to high order detonation of the warhead on earth or water impact. Test E2 – Low altitude Accidental Release: This is a field safety test simulating accidental release of airborne munitions on takeoff or landing. The fuze must not initiate high order detonation when the munition impacts a hard surface.

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Group E – Aircraft Munition Tests c) •

Test E3 – Arrested Lending Pull-off: This is a field safety test simulating accidental release of an airborne weapon upon arrested landing aboard an aircraft carrier.

d) •

Test E4 – Catapult and Arrested Landing Forces: This is a field safety and reliability test. The fuze must withstand forces encountered on catapult takeoff and arrested landing aboard an aircraft carrier.

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Group E – Aircraft Munition Tests e) Simulated Parachute Air Delivery: • This is a safety and reliability test simulating air delivery of packaged fuzes or fuzed ammunitions. The fuze must withstand the forces encountered in lowvelocity, high –velocity and malfunctioning air-delivery drops. BACK

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Group F – Electric and Magnetic Influence Tests These tests are especially used for electronic and electrical fuzes to check their performance variation due to influence of electrostatic discharges, electromagnetic pulses, lightening etc. a) Test F1 – Electrostatic Discharge: • This is a laboratory safety and reliability test simulating possible handling and transportation condition. The fuze must withstand high-potential electrostatic discharge (lightening environment is excluded). BACK

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Group F – Electric and Magnetic Influence Tests b) Test F2 – Electromagnetic Pulse: • This is a laboratory test, which determines fuze ability to satisfy safety and reliability requirements when exposed to a simulated Highaltitude Electromagnetic Pulse (HEMP) environment. This HEMP potential could initiate or alter Electro-Explosive Devices (EEDs) and destroy or damage vulnerable electronic components in the fuze BACK

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Group F – Electric and Magnetic Influence Tests c) Test F3 – EED Susceptibility to EMR: • This is a laboratory safety and reliability test simulating Electromagnetic Radiation (EMR), which may impinge upon the fuze containing Electro-Explosive Devices (EEDs) during their life cycle. Fuze EEDs must withstand the high levels of EMR, which may be encountered during storage, transportation, handling, loading and launching BACK

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Group F – Electric and Magnetic Influence Tests d) Test F4 – Electromagnetic Radiation, Operational (EMRO): • This test is similar to Test F3. It also test that whether Fuze EEDs can withstand the high levels of EMR, which may be encountered during storage, transportation, handling, loading, launching and travel to target. e) Test F5 - Lightening BACK

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APPENDIX B SCHEDULE FOR PROOF AND SENTENCING CRITERIA FOR VT8A FUZE

Proof testing of fuze is carried out to ensure its performance and reliability when subjected to conditions of actual firing. It is based on sampling techniques wherein a sample is randomly chosen and whole lot is accepted or rejected depending upon the performance of sample in the tests. A custom-made proof schedule and sentencing criteria is decided for each fuze which lays down the tests to be carried out, sampling techniques, sample sizes and acceptance criteria.. BACK

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APPENDIX B SCHEDULE FOR PROOF AND SENTENCING CRITERIA FOR VT8A FUZE

• Schedule and sentencing criteria for VT8A proximity fuze is given in this appendix in order to provide an idea about the criticalities and procedure involved in proof testing of fuze. For details, the reader may refer to the catalogues and schedules prepared by CQA (Ammunition), Department of Defence Production & Supplies, Ministry of Defence, Government of India, Khadki, Pune. BACK

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APPENDIX B SCHEDULE FOR PROOF AND SENTENCING CRITERIA FOR VT8A FUZE

• • •

B.1 Store: Fuze VT8A (Empty). B.2 Type of Proof: Empty Filled Proof. B.3 Lot Size: d) Lot 1 to 4: 508 + proof samples. e) Lot 5 onwards: 1008 + proof samples

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APPENDIX B SCHEDULE FOR PROOF AND SENTENCING CRITERIA FOR VT8A FUZE

• • •

B.4 Sample size: Advance samples and upto lot 4: - 46 Nos Lot 5 onwards d) 10th, 20th, 30th Lots: 41 Nos e) 15th, 25th, 35th Lots: 38 Nos. f) Other lots: 33 Nos. BACK

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APPENDIX B SCHEDULE FOR PROOF AND SENTENCING CRITERIA FOR VT8A FUZE

• B.5 Proof Sample Identification: In addition to the marking stamping, proof samples will be marked with Sr. Nos. of proof samples and letter ‘P’ i.e. 1P, 2P, 3P and so on. • B.6 Proof Establishment: Proof and Experimental Establishment, Balasore. • B.7 Conduct of Proof: Normal. BACK

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APPENDIX B SCHEDULE FOR PROOF AND SENTENCING CRITERIA FOR VT8A FUZE

• b) c) d) e) f) g) h)

B.8 Proof Conditions and Component Equipments requested for proof: Proof Sample will be subjected to following conditions. Safety Proof. Arming Proof. Absence of Premature and Short Burst. Functioning proof. Hot condition test: 50oC. Cold condition test: -20oC. Jolted Condition BACK

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APPENDIX B SCHEDULE FOR PROOF AND SENTENCING CRITERIA FOR VT8A FUZE

• B.9 Method of Proof: The proof will be conducted as per details given at Annexure 1. Lotwise conduct of proof is as given below. a) Lot No. 1 to 4: These lots will be subjected to proof as given in Annexure 1. In the case of Cold and Jolt condition, the lots will be subjected to one of the three conditions only. However, it shall be ensured that conditioning as per these conditions is done at least once. BACK

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APPENDIX B SCHEDULE FOR PROOF AND SENTENCING CRITERIA FOR VT8A FUZE

b) Remaining Lots: For remaining lots, proof given at Annexure 1will be carried out except for safety and arming proof. Safety and arming proof shall be carried out with following lots. Further, in five consecutive lots for hot or cold or jolted condition shall be carried out at least once. c) Safety Proof: This proof will be carried out for every tenth lot commencing from Lot No. 15 viz. Lot No. 15, 25, 35 and so on. BACK

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APPENDIX B SCHEDULE FOR PROOF AND SENTENCING CRITERIA FOR VT8A FUZE

d) Arming Proof: This proof will be carried out for every tenth lot commencing from Lot No. 10 viz. Lot No. 10, 20, 30 and so on. e) In an abnormality is noticed in safety and/or arming proof even on one lot, subsequent five lots will be subjected to that proof in which abnormality was observed. If no defect is observed in the proof of these five lots, the cycle of proofing every tenth lot will be resumed thereafter BACK

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APPENDIX B SCHEDULE FOR PROOF AND SENTENCING CRITERIA FOR VT8A FUZE

• B.10 General Conditions of Firing: • B.10.1 Preparation of Proof Sample: a) Fuzes will be assembled with Gaine 1A to Drg No. 1QX 151 GA. Thereafter these fuzes less adapter IQX 853 and Pellet IQX 171 AF will be assembled to Shell 105 mm IFG HEA 1B to Drg No. ISX 67 GF/ISX 77 GF for safety and absence of premature and short burst conditions. b) For remaining conditions given in Annexure 1, the fuzes will be assembled with Shell 130 mm HE to Drg No. ISX 101 GF. BACK

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APPENDIX B SCHEDULE FOR PROOF AND SENTENCING CRITERIA FOR VT8A FUZE

c) For jolt test, fuze fitted with plugs representing Gaine and Dummy CE Pallet will be packed in the approved packages. The packages with fuzes will be jolted in an approved jolting machine through 25mm (to apply 395 + 5 m/s2 acceleration) 15000 times at a rate not more than 2 bumps per second, 5000 bumps at each of these orientations of the fuze i.e. nose-up, nose-down and on the horizontal axis. BACK

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APPENDIX B SCHEDULE FOR PROOF AND SENTENCING CRITERIA FOR VT8A FUZE

• B.10.2 Sensitivity Selection: The fuze is provided with two sensitivities to function at two different height brackets over the target. a) Normal Sensitivity: The fuze is adjusted for normal sensitivity by un-screwing and removal of Contact Screw to Drg No. IQX 857 on the lower body of the fuze. b) High Sensitivity: The fuze is adjusted for high sensitivity by retaining the Contact Screw to Drg No. IQX 857 on the lower body of the fuze. BACK

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APPENDIX B SCHEDULE FOR PROOF AND SENTENCING CRITERIA FOR VT8A FUZE

• B.10.3 Ordnance: Ordnance QF 105/37 IFG and Field Gun 130 mm used in the proof, as given at Annexure 1, should not be beyond the third quarter of life. • B.10.4 Target: Wet Sand or Calm Water (Calm water is defined as having waves of an amplitude of 30 cms or less). • B.10.5 Weather: No Clouds beyond vertical height of trajectory. BACK

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APPENDIX B SCHEDULE FOR PROOF AND SENTENCING CRITERIA FOR VT8A FUZE

• B.11 Observations required: a) Functioning of each round using conventional abbreviations given at B.11(f) below. b) Height of Burst (except for safety, arming and absence of premature and short burst conditions) to be recorded by camera and theodolites. c) Time to burst and range to burst. e) Monitoring data. f) Additional information if any relevant to the functioning of the fuze BACK

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APPENDIX B SCHEDULE FOR PROOF AND SENTENCING CRITERIA FOR VT8A FUZE a)

Definitions and observations:

Abbrev Terms iations

Definitions and Remarks

M

Monitored

To be used as suffix letter to any of the abbreviations to indicate that using flight the fuze oscillations have been monitored.

NM

Not monitored

To be used as suffix letter to any of the abbreviations to indicate that using flight the fuze oscillations have not been monitored.

P

Premature

A Shell, which burst in the bore or within the minimum safety distance of the gaine i.e. up to 40m from the muzzle. BACK 340

APPENDIX B SCHEDULE FOR PROOF AND SENTENCING CRITERIA FOR VT8A FUZE Abbrev Terms iations

Definitions and Remarks

SB

Short Burst

A burst occurring after 40m from the muzzle and before 7-second time of flight.

NB

Normal Burst

For fuze set at “Normal Sensitivity”: A fuze bursting between 3m to 30m from the surface at target end (calm water, wet sand) For fuze set at “High Sensitivity”: A fuze bursting between 15m to 75m from the surface at target end (calm water, wet sand).

EB

Early Burst

A fuze, which operates by VT action between the end of short burst and the upper limit of the normal burst zone. BACK 341

APPENDIX B SCHEDULE FOR PROOF AND SENTENCING CRITERIA FOR VT8A FUZE Abbrev Terms iations

Definitions and Remarks

LAB

Low Air Burst

A fuze, which operates by VT action with a lower limit to normal burst zone and above the target surface.

GB

Ground Burst

A shell, which burst or appear to burst on the target surface

B

Blind

Blind at target surface.

OU

Not Observed

The operations of the fuze not observed by whatever method being used for observations of burst or VT operation BACK

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APPENDIX B SCHEDULE FOR PROOF AND SENTENCING CRITERIA FOR VT8A FUZE • B.12 Sighters: a) Shell 105mm IFG HE A/1B fuzed 117MK – 20 as required will be fired to establish the line of fire and exact location of burst for conditions of Safety proof and Absence of premature and short burst. b) Shell 130mm filled inert with flash pellet to fuze VT 8A (proof stock) as required (about 5 numbers) will be fired for each OP position to get the MPI over the scale markers in the line of fire as an aid to photographic recording of Height of burst of each series, proof samples of particular series will be fired subsequently and burst points recorded with cameras BACK

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APPENDIX B SCHEDULE FOR PROOF AND SENTENCING CRITERIA FOR VT8A FUZE

• B.13 Performance required: a) There must not be any premature or short burst, blind, low air burst and ground burst. b) For functioning proof out of the fuzes recorded as normal burst 50% should be as under: • Normal sensitivity: 15 +7.5m • High sensitivity: 40 + 7.5m • If 50% figure is in decimals the next higher whole number will be taken for sentencing. BACK

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APPENDIX B SCHEDULE FOR PROOF AND SENTENCING CRITERIA FOR VT8A FUZE

• B.14 Classification of defects: a)Critical defects: Premature or short burst. b)Major defects: Blinds (monitored and non monitored), early burst, low airburst and ground burst.

BACK

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APPENDIX B SCHEDULE FOR PROOF AND SENTENCING CRITERIA FOR VT8A FUZE • B.15 Sentencing: a) The proof conditions and sentencing will be in accordance with the sampling plan given in Annexure 1. If a short burst occurs during any firing for proof, further firing will be suspended and lot will be rejected. The quality assurance authority and manufacture will be informed immediately. b) Should the defects recorded during the proof indicate that the cause is due to defects other than the empty fuze under proof, the QA authority may call for any further test/firing to establish this and if so established, the lot may be considered for acceptance without any further proof, based on the general performance of the fuzes during proof. BACK

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APPENDIX B SCHEDULE FOR PROOF AND SENTENCING CRITERIA FOR VT8A FUZE

c) Should firing proof or examination of any lot bring to the notice any defects which in the opinion of the QA Authority affects the serviceability of the fuze, the lot in question may be rejected for further proof taken at his discretion not only from the particular lot, but also from adjoining lots made by the contractor, to ascertain whether the defects is general. Should the fuze fail at these and further proof the lots may be rejected without reference to any previous proof. BACK

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APPENDIX B SCHEDULE FOR PROOF AND SENTENCING CRITERIA FOR VT8A FUZE

d)If a premature occurs, firing will be suspended and cause of premature will be investigated. Further proof sentencing of the lot under proof to be conducted, after getting clearance from the QA Authority

BACK

348

ANNEXURE 1

• S. No

Proof conditions

AQL : 15% Ordnance

REF: DEF 131A Charge

Sensitivit y

QE

Sampling plan

Sample size

Sentence A

R

Remarks A

R

1

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