Siemens Internship Report

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Internship Report Of Siemens (Pakistan) Engineering Company Limited

SUBMITTED TO: Mr. Kamran Saeed Senior Executive Engineer FS Department SUBMITTED BY:

Rehan Ahamd Baig (BS-EE) University of Management and Technology DATED: September, 16, 2011

Rehan Ahmad Baig (UMT)

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FS Department

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PREFACE Internship program is a fundamental part of professional studies. On one side, our theoretical knowledge helps us to understand the basic phenomena of any system and on the other side; internship provides us the opportunity to get a  practical and hands on experience of our knowledge. Here we learn how to apply and materialize that abstract truth into practice in our life. In this experience students attain the opportunity to work outside their institutions and form a satisfactory relationship relationship between their theoretical and practical work to build a new wave of confidence among them. Internship opens the door of practical knowledge to students so that they find no problem when they step in their professions. My organization was Siemens (Pakistan) Engineering Company Limited, where I worked in Field Services (FS) Department for Four weeks.

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Acknowledgment All Gratitude is to Almighty ALLAH, the most Gracious and the most Merciful who gave me the strength and will to do this work. First I would like to thank Siemens Pakistan for inviting me to spend a summer-internship and gave me the honor to work there. What makes this place so special? Not only the perfect infrastructure, the nice working atmosphere, and the large experience and knowledge gathered there, which all serves as a stable basis for further completing my degree. Also not only the company, but the members of it which helped me in every problem I had there. By this I achieved better and higher than what I was expecting. The harder it is to keep up with these high requirements on one hand, the sweeter the feeling to have them matched on the other hand. I highly appreciate the opportunity that had been given to me form leading company of the world and let me study their present work at various levels, thanks for everything I learned.  Next, I would like to thank Mr. Mohammad Mohsin an Executive Engineer in BU-Field Services of Siemens Pakistan Lahore Division for teaching me the basics of the work in the department. He is one of the very competent engineers. The work, the first advices and recommendations he gave me will serve as a good basis for my future work. I thank him for supplying me with good recommendations. I have to mention nice time out and discussions with him. He was always ready to enter discussions of new topics, ideas, and results. His expertise always served me as a good example. I am very grateful to Mr. Shafqat  an Executive Engineer in BU- Field Services of Siemens Pakistan Lahore Division. The atmosphere has always been a perfect source of o f motivation. It was great to be welcomed and introduced to him. It was pleasure to share office with him. Who was the person “infecting” me to spend more working hours a week. We shared not only nice discussions during work, but also nice time. I am very grateful to him who always took the time to answer my questions thoroughly sometimes even to the very depths. I have to specially mention a long-standing co-intern and friend, Hassan Zafar. Together we  proved that long distance cannot be an obstacle for effective co-actions. He was always read y to enter discussions of new topics, ideas, and results. We shared the table while working. I also enjoyed sharing few evenings out with him. I thank also all others who were always willing to help, discuss some topic. Last, I want to thank my parents, without whom I would never have been able to achieve so much. I thank for their endless love, patience, and understanding. Rehan Ahmad Baig (UMT)

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Preface………………………………………………………………….....2 Acknowledgment……………………………………………………….…3 Executive Summary……………………………………………………….5 Introduction ………………………………………………………..….….6 Company History……………………………………………….…..…….7 Siemens Pakistan History…………………………………………………9 Vision Statement……………………………………………………… ..11 Mission Statement……………………………………………………….12 Field Services…….…………..…………………………………………..13 AC Motors…….………………………………………………….……...14 Induction Motors………………………………………………………...16 Motor Parts…………………………………………………………….....19 AC Motor Starters …………………………………………………….....22 Comparison Overview……………………………………………………27 Speed Control of DC Motor…………………………………………...…28 Speed Control of AC Motor…………………………………………...…29 Programmable Logic Controller………..………………………………...31 S7-Simatic Manager…………………………………….………………..36 Hardware configuration with S7…………………………………………39 Programming language Ladder Diagram LD, LAD……………………..44

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Counter and Timer……………………………………………………….47 Programming language FBD…………………………………………….49 SIMATIC S7-300………………………………………………………..54 Types of Block…….…………..…………………………………………59 Types of Data…….………………………………………………………60 Programming Devices…………………………………………………....61 Human Machine Interface……………………………………………….62 SCADA………………………………………………………………….63 WinCC flexible………………………………………………………….63 Assignments……………………………………………………………..66 Experience…………………………………………………………….…67 Internship Accomplishments…………………………………………….67 Conclusion……………………………………………………………….68

��������� ������� This report is a comprehensive description of business activities and operational procedures of FS Department of Siemens Engineering Company limited. The report begins with the in depth study of Siemens and the people of Siemens. Siemens is a multinational company based in Germany. During my internship of Four weeks in Siemens Lahore, I was in FS Department of the company where I learned its working principles. Besides the customary learning, the moral and sound discussion of my Supervisor also made be able to understand the ethics of doing work in an organization.

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������������ Siemens enjoys a leading position in Pakistan in the business areas of Power, Automation and Control, Medical, Transportation, Information Technology and Industrial solutions. Siemens is the country’s No. 1 supplier of high-voltage grid stations, switchgear products and systems,  power distribution and power transformers, and network consultancy. The Power Generation Group is a major player in the country. To date, the Group has added over 2,500 MW to Pakistan's power generation capacity. The Industrial Automation & Drives Technologies Group is the only major local supplier with 35 years of experience in the local manufacture of diesel generating sets to meet customer specific demands from clients on both the domestic and international markets. The success story continues with the Medical Solutions Group, which is the leading supplier of state-of-the-art equipment to major hospitals. With a workforce of over 1500 employees, Siemens is one of the most important employers in the country. Siemens is also the single largest employer of engineering graduates in the country. It follows a policy of gender equality.

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COMPANY HISTORY “Siemens AG is Europe's largest engineering conglomerate. Siemens was founded by Werner von Siemens on 12 October 1847. Based on the telegraph, his invention used a needle to point to

the sequence of letters, instead of using Morse code. The company, then called TelegraphenBauanstalt von Siemens & Halske , opened its first workshop on October 12.” Werner von Siemens:

Made the world's first pointer telegraph

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Made the Electric dynamo

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Constructed the world's first electric railway

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Laying the first telegraph line linking Britain and India

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Built much of the modern world's infrastructure.

Siemens is today a technology giant in more than 190 countries, employing some 475,000 people worldwide. They work in the fields of

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Energy

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Industry

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Healthcare

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Different Era’s of Siemens:-

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Beginnings and early development

[1847 – 1865]

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Company policy and international projects

[1865 – 1890]

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The second generation

[1890 – 1918]

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A period of transition

[1918 – 1933]

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The National Socialist war economy

[1933 – 1945]

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Postwar reconstruction and emergence as a global player

[1945 – 1966]

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United under a single roof

[1966 – 1989]

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Stepping into the third millennium.”

[1989 – 2005]

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SIEMENS PAKISTAN HISTORY 

Siemens first office in Lahore

[ 1922 ]

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Cable laying project in Karachi.

[ 1932 ]

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The Pak Industrial & Trading Corp. Ltd. is appointed to represent SSW in Karachi. [ 1950 ]

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Siemens cooperates with the Pakistani government to build a production plant for manual and automatic telephone systems in Haripur. The joint venture Telephone Industries of Pakistan (TIP) is formed.

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[ 1952 ]

Siemens Pakistan Engineering Co. founded as Private Limited Company. [ 1953 ]

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Switchboards production commenced.

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The Pakistani government awards Siemens Karachi a contract to build a production plant for

[ 1957 ]

motors, transformers and switchgear. 

[ 1960 ]

Siemens Karachi succeeds East Asiatic Company (EAC) as representative of SRW. The railway administration awards Siemens a contract to modernize the railway safety installations in West and East Pakistan.



[ 1961 ]

Siemens became Public Limited Company & Factory for Motors & Transformers. [ 1963 ]

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Siemens builds a telephone plant in Tongi and a phone cable factory in Khulna. Telephone Industries Corporation (TIC) is founded in Dacca, and Industries of Pakistan (CIP) is established in Khulna.

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[ 1967 ]

Siemens and the Pakistani government form a joint venture named Carrier Telephone Industries (CTI), Islamabad.

[ 1969 ]

Introduction of Diesel Generating Sets

[ 1967 ]

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Power Transformers production started~30MVA

[ 1981 ]

Extension in Power Transformer rating~60MVA

[ 1987 ]

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The company begins setting up a GSM mobile radio network

[ 1993 ]

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412 MW Rousch Combined Cycle Power Plant

[ 1996 ]

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Become first Value Added Reseller of SAP

[ 1998 ]

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Export order for 132 kV substation for DEWA Dubai, UAE

[ 2000 ]

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Launched 1.1 MVA DG Sets

[ 2002 ]

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Signed agreement for first desalination plant in Karachi

[ 2003 ]

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Launched new line of Low Voltage Switchgear System of family SIVACON 8PT.



[ 2004 ] 

11 Grid Stations 220kV/132kV for KESC & Acquired Carrier Telephone Industries [ 2005 ]

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 New Jabel Airport and Dubai Sports City 132KV Grid Stations, UAE & Ghakkar 500kV Grid Station, WAPDA

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[ 2006 ]

SAP implementation in PTCL Siemens Pakistan pioneered to manufacture 220 kV/250 MVA Power & Transformers in Pakistan

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[ 2007 ]

 New Jebel Ali Airport 132kV Grid Stations Extension Project, UAE & Inauguration of Desalination Plant for DHA Cogen Ltd

Rehan Ahmad Baig (UMT)

[ 2008 ]

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SIEMENS VISION STATEMENT

To remain market leader and technology pace setter in the engineering and electronics industry by utilizing the h igh tech engineering expertise of the siemens group worldwide to maintain our strong and  prominent local presence.

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Business Divisions: Following is the overview on some of the Siemens’s businesses: •

Power Transmission and Distribution:

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HV-Sub-Stations:

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Transformers:

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Switchgears:

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PTD Services:

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Industrial Solutions & Power Generation:

•

Process Industries & Water Technologies:

•

Engineering and Construction:

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Power Generation:

•

Information Technology Services:

•

Field Services:

•

Siemens Building Technologies:

•

Industriel Automation & Drives Technologies Division:

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Generating Sets:

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Healthcare Sector:

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Medical Solutions:

•

OEM Onshore:

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Transportation Systems:

•

Finance and Controlling:

•

Energy Automation:

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Field Services: (On-Call, Logistics & Maintenance Services)

Master your future with Siemens Maintenance Services. If your top priorities are optimum availability and operating efficiency of your equipment, plant or industry, you should demand the best from your service partners. Siemens Maintenance Services will live up to your demands. As specialists for complete electro mechanical maintenance, we are your competent & experienced partner for all the repairs, maintenance and revamps. A partner who gives every thing to meet your priorities with reliability and from a single source. You as Siemens customer are the benchmark by which we evaluate our performance- day by day. To facilitate reliable, failsafe production facilities, innovative technologies & superb after sales support Siemens Pakistan has a dedicated Business Unit i.e. “OnCall-, Logistics & Maintenance Services.

Field Services use the technological & business management competencies, as well as their vast  project execution & maintenance experiences enable them to provide sustainable support throughout the production phase of the industry; that help their customers to achieve their  business goals more effectively . To stay competitive, it is essential to have a maintenance and modernization plan that addresses  both technical and business issues. It is only when the need for performance and profitability are  balanced that the desired results can be achieved. Customer equipment must be up-to-date,  processes must be highly available and any improvements they make to their production facilities must deliver favorable Profits. When modifications are made - from reconstruction and expansion to site relocation - all downtime must be kept to a minimum. FS can do that: by using the unsurpassed combination of technological expertise and industryspecific experiences.

Services at a glance: 

Repair, Overhauling & Maintenance of Motors & Alternators

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Condition Monitoring (Thermography, Vibration Analysis, NDI & Oil Analysis)

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Spare Parts Management

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Operation & Maintenance Service (Industrial and P ower Plants)

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AC motors With the almost universal adoption of AC system of distribution of electric energy for light and  power, the field of application of AC motors has widened considerably during recent years. It consists of two basic parts, an outside stationary stator having coils(Armature windings) supplied with alternating current to produce a rotating magnetic field, and an inside rotor (Field windings)attached to the output shaft that is given a torque by the rotating field. Main types are: 1) Synchronous motor 2) Asynchronous motor a) Induction motor i) Single Phase motors ii) Three Phase motors

Synchronous motor: A synchronous motor is similar to an alternator with a rotating field. The stator of a synchronous motor is the same as that of the more popular induction motor. A 3-phase synchronous motor generates an electrically rotating field in the stator. Such motors are not self starting if started from a fixed frequency power source. It

runs either at synchronous speed or not at all. It is not inherently self starting. It has to be run at synchronous sped by some means before it can be synchronized to the supply. A wound rotor (rotating field) which has the same number of poles as the stator, and is supplied by an external source of direct current (DC). Both brush-type and brushless exciters are used to supply the DC field current to the rotor. The rotor current establishes a north/south magnetic pole relationship in the rotor poles enabling the rotor to “lock-in-step” with the rotating stator flux.

Procedure for starting: Field winding is shorted Stator voltage is reduced. The motor starts up. At steady speed, DC excitation is applied and short-circuiting of field winding is removed. Full voltage is applied at stator.  Now motor can be operated at any power factor by changing the DC excitation.

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Features: For a given frequency it runs at a constant average speed whatever the load is. It can operate over a wide range of power factors, both lagging and leading.  Not self starting DC excitation is required. Can be run at ultra low speed by using high power electronic converter which generates very low frequency.

Applications: Power factor improvement. Voltage regulation. Constant load drives.

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Induction Motor: Most AC motors are induction motors. Induction motors are favored due to their ruggedness, simplicity (absence of brushes) and the ability to control the speed of the motor. In fact, 90% of industrial motors are induction motors. The induction motor does not have any direct supply onto the rotor; instead, a secondary current is induced in the rotor. An induction motor is sometimes called a rotating transformer   because the stator (stationary part) is essentially the primary side of the transformer and the rotor (rotating part) is the secondary side. Induction motors are widely used, especially polyphase induction motors, which are frequently used in industrial drives.

Working Principle: A conductor moving through a magnetic field will have a voltage induced into it. This is known as “Electromagnetic Induction” .This electrical principle is used in the operation of AC induction motors. The basic difference between an induction motor and a synchronous AC motor is that in the latter a current is supplied onto the rotor. This then creates a magnetic field. By way of contrast, the induction motor does not have any direct supply onto the rotor; instead, a secondary current is induced in the rotor. To achieve this, stator windings are arranged around the rotor so that when energized with a polyphase supply they create a rotating magnetic field  pattern which sweeps past the rotor. This changing magnetic field pattern induces current in the rotor conductors. This current interacts with the rotating magnetic field created by the stator and in effect causes a rotational motion on the rotor.

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However, for these currents to be induced, the speed of the physical rotor and the speed of the rotating magnetic field in the stator must be different, or else the magnetic field will not be moving relative to the rotor conductors and no currents will be induced. This difference between the speed of the rotor and speed of the rotating magnetic field in the stator is called “ slip”.

The rotor speed is:

Where s is the

 slip

Slip is calculated using:

Slip can never be zero in an induction motor. At the start it is 100%. It should be as small as  possible, not more than 5%.

Construction:

Stator: The stator is the stationary part of the motor. The stator core is cylindrical made up of several thin laminated sheets Silicon steel. These laminations are stacked together forming a

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hollow cylinder. There are slots in the inner periphery. Coils of insulated wire i.e. armature windings are inserted into slots of stator core. Each grouping of coils, together with the steel core it surrounds, form an electromagnet. Electromagnetism is the  principle behind motor operation. The stator windings are connected directly to the power source.

Rotor: The rotor is moving part of motor. Induction motor has two types of rotors.

Squirrel-cage rotor: The most common rotor is a squirrel-cage rotor. Core is made up of laminated sheets of Silicon steel. Slots are present on outer periphery of core and Al conductors (bars) are placed in these slots. These conductors are forming closed circuit i.e. copper rings at each end. No terminals are coming out of it. The rotor bars in squirrel-cage induction motors are not straight,  but have some skew to reduce noise and harmonics.

Slip-ring rotor: A slip ring rotor replaces the bars of the squirrel-cage rotor with copper windings that are connected to slip rings. These rings are mounted on rotor but laminated from the rotor. These can also be connected to resistors to produce a high-resistance rotor circuit, which can be beneficial in starting.

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Motor Parts

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AC motor starters Synchronous motor: Three basic approaches can be used to safely start a synchronous motor

1. Reducing electrical frequency: If the stator magnetic field in a synchronous motor rotates at a low enough speed, there will be no problem for the rotor to accelerate and to lock in with the stator magnetic field. The speed of stator magnetic field can then be increased. This approach to starting synchronous motor makes a lot of sense but it does have one  problem i.e. variable frequency source. Regular power systems are much regulated at 50 or 60 Hz, so we need a variable frequency voltage source. Today variable frequency drives, cycloconverters are very common in industries. In this method AC is rectified to DC and then controlled AC is obtained from this DC using inverters. This method is very easy- simply adjust the frequency to a very low value for starting, and then raise it up to the desired frequency for normal running.

2. by external prime mover: This approach to starting a synchronous motor is to attach an external starting-motor to it and bring the synchronous motor up to full speed. The starting motor only needs to overcome the inertia of the synchronous motor without a load, so starting motor can have a much smaller rating than the synchronous motor it starts. Since most large synchronous motors have brushless excitation systems mounted on their shafts, it is often possible to use these exciters as starting motors.

3. Using Damper windings: This is a very popular way to start a synchronous motor by employing damper windings. Damper windings are special bars laid into notches carved in the face of synchronous motor’s rotor and then shorted out on each end by a large shorting ring. Using damper windings motor can be started by the following procedure: • •

•

Disconnect the field windings from DC source and short them out. Apply a three phase voltage to stator, and let the rotor accelerate up to near-synchronous speed. The motor should have no load on its shaft. Connect the field windings to its power source. After this is done, motor will lock into step at synchronous speed and can then be loaded.

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Induction motor: Types of starters: 1. 2. 3. 4. 5. 6.

Direct on line starter Autotransformer starter Star Delta starter Resistance starter Soft start Series reactor starter

1. Direct on line starter: The main method of starting the AC motor is direct-on-line starting. This simply means an electro-mechanical switch is opened and closed to stop and start the motor. When an induction motor starts DOL, a very high current is drawn by the stator, in the order of 5 to 9 times the full load current. This high current can, in some motors, damage the windings; in addition, because it causes heavy line voltage drop, other appliances connected to the same line may be affected by the voltage fluctuation. To avoid such effects, several other strategies are employed for starting motors.

Disadvantages:  Electrical:

• •

• •

High inrush current (typically 6 x full load which can cause several problems).  Necessities over sizing of installation (particularly important on generator and UPS fed supplies). Limits Expansion. Reduces service life of electrical components.

 Mechanical:

• • •

Excessive applied starting torque (typically 2.5 x full load). Increases wear on drive chain components. Reduces service life of mechanical components.

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2. Autotransformer starter: This method uses transformer action to reduce the voltage applied to the motor and current seen by the supply. An improved torque/amp ratio is achieved and starting current is typically 3 x FLC, depending on the voltage rapping selected. Normally the voltage is applied to the motor in voltage steps through the transformer with the taps being selected through contactors. Typical tapings are 50%, 70%, followed by full voltage being applied to the motor. The major disadvantages are size and cost, and of course the mechanical snatch at switch on is not controllable and can still cause problems. Also once the tapings have been selected, it may be necessary to change them according to changes in load parameters.

Advantages: •

Simple operation.

Disadvantages: • • •

Poor controllability Bulky Very Expensive

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3. Star delta starter: An induction motor's windings can be connected to a 3-phase AC line in two different ways: •

•

Wye ( star  in Europe), where the windings are connected from phases of the supply to the neutral;  Delta (sometimes mesh in Europe), where the windings are connected between phases of the supply. A delta connection results in a higher voltage to the windings than a wye connection (the

voltage is multiplied by ). A star-delta starter initially connects the motor in wye, which  produces a lower starting current than delta, then switches to delta when the motor has reached a set speed.

Disadvantages of this method over DOL starting are: •

•

•

Lower starting torque, which may be a serious issue with pumps or any devices with significant breakaway torque Increased complexity, as more contactors and some sort of speed switch or timers are needed Two shocks to the motor (one for the initial start and another when the motor switches from wye to delta)

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4. Resistance starter: This method is used with slip ring motors where the rotor poles can be accessed by way of the slip rings. Using brushes, variable power resistors are connected in series with the poles. During start-up the resistance is large and then reduced to zero at full speed. At start-up the resistance results in the stator's field strength being weakened less. As a result, the inrush current is reduced. Another important advantage is higher start-up torque. As well, the resistors generate a phase shift in the field resulting in the magnetic force acting on the rotor having a favorable angle.

5. Soft start: The soft start is designed to apply an adjustable voltage to the motor and increase this voltage gradually over a user-selectable acceleration period. The acceleration time being dependent on the application and desired characteristics. The added advantage of this method of reduced voltage control is that the motor can also be stopped gradually by slowly reducing the output voltage to the. ‘Soft Stop’ feature offers a smooth stop in many process industries such as  pumps, where fast stops can result in ‘water hammer’ and mechanical damage.

Advantages: • • • •

Reduced starting current Reduced starting torque Less mechanical stress Improved control of acceleration and deceleration

6. Series Reactor starter: In series reactor starter technology, an impedance in form reactor is introduced in series with the motor terminals, which as a result reduces the motor terminal voltage resulting in the reduction on the starting current, the impedance of the reactor being the

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function of the current passing through it, it gradually reduces as the motor accelerates, and at 95 % speed the reactors are bypassed by a suitable bypass method which enables the motor run at full voltage and full speed. Air core series reactor starters or a series reactor soft starter is the most common and recommended method for fixed speed motor starting.

Comparison Overview

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Speed Control of DC Motors Speed of DC motor can be controlled by varying Flux/Poles • •

Armature resistance

•

Applied voltage

DC Shunt motor: The speed controlling techniques of DC shunt motors are as follows:

Flux control method:    

The flux of DC motor can be changed by changing Shunt current. A field rheostat is used to change current. Rheostat must be small because shunt current is v ery small. Speed can be increased in ratio of 2:1.

Armature or Rheostat control method:  Voltage across armature is varied by inserting rheostat or resistance in series with

armature.  Resistance causes decrease in p.d across armature thereb y decreasing armature speed.  This method is useful when speed below no load is required.

Multiple voltage control :  Shunt field is connected permanently to a fixed excitation voltage.  Armature voltage is varied by means of switch gears.  Armature speed would be proportional to applied voltage.  This method is less common.

DC Series motor: The speed controlling techniques of DC series motors are as follows:

Flux control method: 1. Field Divertors:  Series winding is shunted by a variable resistance known as shunt divertor.  Flux can be varied adjusting resistance, hence speed can be varied.

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���������� ������ 2. Armature Divertor:  Divertor across armature can be used for speed lower than normal speed.  Variation in speed can be controlled by varying resistance. 3. Paralleling field coils:  This method is used for fan motors.  Several speeds can be obtained by regulating field coils.

Variable resistance in series:  Armature voltage can be regulated by variable resistance.  Full motor current passes through resistance so loss of power is caused.

Compounded DC motors:  Changing field resistance.  Changing armature voltage.  Changing armature resistance

Speed Control of AC Motors AC motors particularly, squirrel cage and wound rotor induction motors as well as synchronous motors lend themselves to well to electronic control of their speed and torque. Such a control is usually exercised by varying frequency or voltage. These AC drives can be grouped under the following categories: •

Static frequency changers.

•

Variable voltage controllers.

•

Variable current controllers.

•

Rectifier inverter system.

Variable frequency speed control of SCIM: These devices are basically cyclo-converters which convert incoming high line frequency directly into the desired low load frequency. The stator voltage is adjusted in  proportion to the frequency in order to maintain a constant flux in the motor. A small part of reactive power required by SCIM is provided by cyclo-converters and the rest is applied by 3 phase line. Hence power factor is poor which makes cyclo-converter drives feasible only small and medium power induction motors.

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Variable voltage speed control: These controllers vary the speed and torque of motor by varying stator voltage with the help of SCRs. The stator voltage is reduced by delaying the firing of thyristors. Power factor is low due to large lagging current hence these devices are feasible for motors rated below 15KW. Due to distortion of voltage power losses are much more.

Speed control of SCIM with rectifier inverter system: Rectifier inverter system with a DC link is used to control speed of SCIM. The line AC voltage is first converted into DC and then controlled AC is produced. Basic Drive System: The adjustable frequency drive consists of following sections: Line voltage – 3- phase AC. •

•

•

•

•

Input Section - Consists of a rectifier and filter. Transforms the AC voltage into DC voltage. Control Section - The control board accepts real world inputs and performs the required operations. The tasks are performed by a microprocessor. Output Section - This section includes the base drive circuits and the inverter. The base drive signals are low level signals that tell the inve rter to turn on. Motor.

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PROGRAMMABLE LOGIC CONTROLLER

Programmable Logic Controller: Generally defined as:

A Programmable Logic Controller is a user-friendly, microprocessor based, specialized computer carrying out control functions of many types and level of complexity in industrial applications. According to NEMA a PLC is:

A digital electronic device using a programmable memory to store instructions and implement specific functions such as logic, sequence, counting, timing and arithmetic to control machines and processes.

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PROGRAMMABLE LOGIC SYSTEM DIAGRAM

A PLC in an Automated System is like:

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Scan Time of a PLC: •

•

•

Input scan at which input terminals Are read and the input status table is updated. Program scan at which data in the input status table is applied to the user program, the program is executed and the output status table is executed. Output scan at which data associated with the output status table is transferred to output terminals.

Mechanical Design of PLC System: There are two common types of P LC Brick type PLC Modular or Rack type PLC • •

Brick Type PLC: It is available as an integral compact package complete in power supply, processor, memory and input/output modules.

Modular or Rack Type PLC: The modular type consists of separate modules foe power supply, processor etc. which are often mounted on a rail with in a metal cabinet.

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Parts of PLC: A PLC basically consists of two elements: The Central Processing Unit The Input/output System • • •

The Input/output System: The input/output (I/O) system is the section of a PLC to which all of the field devices are connected. The I/O system is what actually physically carries out the control commands from the  program stored in the PLC’s memory. The I/O system consists of two main parts: The Rack I/O Modules • •

• •

The rack is an enclosure with slots in it that is connected to the CPU. I/O modules are devices with connection terminals to which the field devices are wired.

Analog I/O Modules: •

•

•

An analog input interface module contains the circuitry necessary to accept the analog voltage or current signals from analog field devices. Analog input sensing devices include temperature, light, speed, pressure, and position transducer. Analog output devices include small motors, valves, analog meters and display.

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Discrete I/O Modules: •

•

The most common I/O interface module is the discrete type. This type of interface connects on/off type field input devices such as selector switches, push button and limit switches. Output control is limited to devices such as lights, small motors and solenoids and motor starters that require on/off switching.

Central Processing Unit: •

•

The central processing unit (CPU) is the part of a programmable controller that retrieves, decodes, stores, and processes information. It also executes the control program stored in the PLC’s memory. In essence, the CPU is the “brains” of a programmable controller.

Parts of CPU: The CPU has three parts: The processor The memory system The power supply • • •

Processor Unit: The processor unit interprets the input signals and carries out the control actions, according to the  program stored in its memory, communicating the decisions as action signals to the outputs.

Memory unit: The memory system is the section of the CPU that Stores both the control program and data from the Equipment connected to the PLC.

Power Supply: The Power Supply Unit is needed to convert the mains A.C. voltage to the low D.C. Voltage necessary for the processor and the circuits in the input and output interface modules.

A Complete PLC View

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S7-Simatic Manager PLC Projects in Step7

A programming software for Siemens SIMATIC Step7 offers apart from the five pro gramming Languages, defined in the standard Norm EN 61131 further programming languages. In Siemens S7 there are the following types of programs and programming languages:

Programming Languages: • Ladder Logic • Sequential Function Chart (SFC) • Function Block Diagram(FBD) • Structural Text Programming • Instruction List (IL) The languages can be mixed in any way within a PLC project. The unification and standardization of these five languages represent a compromise of historical, regional and  branch-specific requirements. Provision has been made for future expansion, (such as the function block principle or the language Structured Text)  plus necessary information

technology details (data type etc.) have been incorporated. The language elements are explained with the help of a machining process involved in valve  production. Two sensors are used to establish whether a work piece with correctly drilled holes is available at the machining position. If the valve to be machined is of type A or type B – this is set via two selector switches – the cylinder advances and presses the sleeve into the drilled hole.

Ladder diagram (LD) Ladder diagram is a graphic programming language derived from the circuit diagram of directly wired relay controls. The ladder diagram contains contact rails to the left and the right of the diagram; these contact rails are connected to switching elements (normally open/normally closed contacts) via current paths and coil elements.

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Example of ladder diagram language

Function block diagram (FBD) In the function block diagram, the functions and function blocks are represented Graphically and interconnected into networks. The function block diagram originates from the logic diagram for the design of electronic circuits.

Example of function block diagram language

Instruction list (IL) Instruction list is a textual assembler-type language characterized by a simple machine model (processor with only one register). Instruction list is formulated from control instructions consisting of an operator and an operand. OR Part TypeB AND Part Present AND Drill_ok ST Sleeve in LD Part TypeA Example of instruction list language

Structured text (ST) Structured text is high-level language based on Pascal, which consists of expressions and instructions. Instructions can be defined in the main as: Selection instructions such as IF...THEN...ELSE etc., repetition instructions such as FOR, WHILE etc. and function block invocations. Sleeve_in : = (Part_TypeA OR Part_TypeB) AND Part_Present AND Drill_ok ; Example of structured text language

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Structured text enables the formulation of numerous applications, beyond pure function technology, such as algorithmic problems (high order control algorithms etc.) and data handling (data analysis, processing of complex data structures etc.).

Sequential function chart (SFC) The sequential function chart is a language resource for the structuring of sequenceoriented control programs. The elements of the sequential function chart are steps, transitions, alternative and  parallel branching.

With regard to language philosophy, the ladder diagram, the function block diagram and instruction list have been defined in the way they are used in today’s PLC technology. They are however limited to basic functions as far as their elements are concerned. This separates them essentially from the company dialects used today. The competitiveness of these languages is maintained due to the use of functions and function block.

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Hardware configuration with S7

The CPU has to know, which hardware is available Before a control with Sep7 can be projected and put into operation, the present hardware has to  be configured in S7. Without the hardware configuration of the PLC and the connected blocks as for example, input- and output blocks, power supply and so on, the installation cannot be put into operation. In the hardware configuration the available hardware (power supply, CPU, blocks and profile rail) are listed in S7. After the blocks are addressed and parametered as required. Finally this configuration is loaded in the CPU. This is necessary because the CPU has to know which blocks are available, how they are addressed and parametered.

Create new project Process of the hardware configuration

In order to carry out the hardware configuration a project is needed first. Either the project is available already or a new project, as in this example, is set up.

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For doing so open the menu options FILE- NEW. Alternatively you could activate the assistant for a new project or, as long as you want to open an existing project click FILE- OPEN to open and edit an existing project.

Enter project name

Assign a project name to the project. In this case our project is simply called "project name". The location in which this is filed can usually stay as it is in the pre-selection. Unless you would like to store the project in a different location. In this case choose a different file. Confirm the inputs with OK.

Insert station

Subsequently the new project is generated and the SIMATIC Manager is started. First according to the SIEMENS block available (S7-300, S7-400 etc.), a station has to be included. In ours we would like to include a Siemens S7-300 station. First, mark the project in the left field. Via the menu options INSERT-STATION and the corresponding choice of the stations, eg. S IMATIC 300-station, you can insert a new station.

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Open hardware configuration

The station is inserted below the project node. The next step is opening the hardware configurations. Here there are a variety of methods as it is often the case. Either, like in our example via the right mouse button and the menu option OPEN or with a double click on the symbol HARDWARE on the right side of the window. Subsequently the program HW configuration is opened in a new window. First the window is empty. In the right field you will find the hardware catalogue. Here all blocks are listed in various nodes which are available in the current hardware catalogue. Like in reality first a profile rail has to be included which the blocks can be mounted onto. Only then the power supply, the CPU and input- and output blocks can be inserted. For this open the node for the station, in this example SIMATIC 300, then the node rack-300 and drag the profile rail via drag and drop in the left field of the window. Subsequently the profile rail together with the various slots is shown in the left field of the window and the single components can be inserted also via drag and drop.

Basis for the set of the units is the profile rail

The single components are now dragged via drag and drop on the profile rail. On each block there is an order number. In the lower field of the hardware catalogue the corresponding order number to the marked object is indicated, eg. 6ES7 322-1BL00-0AA0. Thus a description mistake is prevented, if, eg. various blocks have the same label. This is in particular tricky for input- and output blocks.

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In our example we have inserted the power adaptor PS307 5A, the CPU 315, the input block DI 32xDC24V and the output block DO 32xDC24V/0.5A.

The components are drawn on the profile rail via drag and drop

Before the configuration is loaded in the CPU the specifics of the single blocks can be read and  partly be changed, for example the MPI-address of the CPU. For doing so open the corresponding block with a double click. In our example we have opened the specifics window of the CPU and can read and change the specifics in the corresponding register.

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Customizing of the properties

Finally the configuration has to be loaded in the CPU. We advise you to save the configuration under STATION - SAVE before. In order to load the configurations in the CPU open the menu option PLC - DOWNLOAD and in the next window choose the CPU. Subsequently the hardware configuration is loaded in the CPU. The loading of the configuration data can also be made vice versa. The data can be loaded from the CPU in the program and after having made certain adjustments they can be loaded back again in the CPU. In order to read out the data from the CPU choose the menu option PLC - UPLOAD.

Loading into CPU

The CPU After the configuration have been saved and finished the hardware turns up in the Simatic Manager below the station. In our example we successfully inserted the CPU 315, the digital input- and output modules as well as the power supply. Only now it is possible to start with the installation of the S7 program, which can be inserted in the node below the CPU.

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Programming language Ladder Diagram LAD: The graphic programming language ladder diagram LD has its idea from the representation of current flow charts. It is programmed with the symbols known from the current flow charts symbols, like NC contact, NO contact or coils and lamps. In networks they are connected as logic structures. By using symbol tables a ladder diagram is gaining more visual clarity, as the operands are directly indicated with names and labels, like, eg.lamp_EMERGENCYSTOPx for fact flags, LSx for light barrier, the output Q2.5 as motor_ON or similar. Example for the representation of the lamp EMERGENCYSTOP in LD without symbolic: Q4.0 Example for the representation of the lamp EMERGENCYSTOP in LD with symbolic: Lamp_EMERGENCYSTOP Example for the representation of the end switch feed in LD without symbolic: I2.0 Example for the representation of the end switch feed in LD with symbolic: Endswitch_feed The graphic programming language LD, also called in Step7 as LAD, is part of the basis software SIMATIC Step7 and is mainly used for the creation of logic operation controls. The creation of programs with the programming language LD is made with an incremental editor. The logic progress of a programmed logic operation control in the programming language LD is represented from left to right and from the top to the bottom. This is according to the program  processing in Step7. The used switching symbols are determined in the standard DIN 19 239. As the programming language LD is represented according to the idea of the representation of current flows charts for connector circuits, the study of the language for those who are familiar with current flow charts is not a problem. Counters, times, jumps and other can be integrated in the ladder diagram via an additional function easily.

The logical AND-operation

Logical AND-operation An logical AND-operation consisting of two inputs I0.0 and I0.1 and an output Q0.0 is represented in the graphic programming language LD as follows. The logical OR-operation

Logical OR-operation An logical OR-operation consisting of two inputs I0.0 and I0.1 and one output Q0.0 is represented in the graphic programming language LD as follows. The logical XOR (Exclusive-OR) operation

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XOR-operation

In order to represent a logical XOR-operation (Exclusive-OR) in the graphic programming language LD, a network must be created with NC contacts and NO contacts.

Comparison instructions in LD In the programming language ladder diagram LD the two inputs IN1 and IN2 can be compared as follows: == IN1 is equal IN2 IN1 is unequal IN2 > IN1 is greater than IN2 < IN1 is less than IN2 >= IN1 is greater or equal IN2