Chap 3 Signal Conditioning Circuit

2/23/2014

MECHATRONIC SYSTEM DESIGN

SIGNAL CONDITIONING 

Outlines • • • • • • • •

Conditioning Circuits Circuits Elements Power Supply DC Voltage Divider AC Voltage Divider Wheatstone Bridge Operational Amplifiers Filters

1

2/23/2014

Introduction

������������ �������� 

 A signal conditioning circuit contains many  elem elemen ents ts that that are are used used to: to:   Adjust the level of signal.  Remo Remove ve nois noisee from from the the sign signal al  Conve Convert rt the the sign signal al



It can also be used to:  Supp Supply ly powe powerr to the the se sens nsor or circ circui uitt Protec ectt the the sens sensor or circ circui uit. t.  Prot

2

2/23/2014

Circuits Elements

    

Power supply   Voltage divider/ Wheatstone bridge  Amplifiers Filters DAC/ ADC See in DAQ

Power Supply  

Battery  

 Advantages:  Least expensive  Constant voltage  Large current flow.



Disadvantages:   Voltage decay with time under load  Replaced when dead  Recharged when empty 

3

2/23/2014

Zener Diode 

 A zener diode can be used to regulate the output voltage from a battery.



 As long as V s >V z in reverse bias, the output voltage V o= V z

Vs

Vz

Power Supply   

 We could also use the AC line power supply. But we need to regulate it (convert AC to DC).

4

2/23/2014

Power Supply  

The transformer converts the main supply to low output AC voltage..

Power Supply 

The rectifier converts the low AC voltage to a varying DC voltage.

5

2/23/2014

Power Supply 

A capacitor can be used to smooth the varying DC voltage.

Power Supply 

The ripples can be removed by using a regulator (a circuit with zener diodes)..

6

2/23/2014

DC Voltage Divider 

DC voltage divider

 AC Voltage Divider 



The two impedance voltage divider is used often to supply a voltage different from that of an available AC signal source. In application the output voltage depends upon the impedance of the load it drives.

7

2/23/2014

Voltage Divider 

Q: What happens when R 1 and R 2 is changed by  R 1 and  R2 ? What is the expression for  V out?



Q: What happens when Z1 and Z2 is changed by   Z1 a n d  Z2? What is the expression for  V out?

 Wheatstone Bridge 



 A basic Wheatstone bridge circuit contains four resistances, a constant voltage input, and a voltage gage, as illustrated  below. For a given voltage input V in, the currents flowing through  ABC  and  ADC  depend on the resistances, i.e.,

8

2/23/2014

 Wheatstone Bridge The voltage drops from  A to  B and from  A to  D are given by,

The voltage gage reading V g can then be obtained from,

Wheatstone Bridge •

•

Now suppose that all resistances can change during the measurement. The corresponding change in voltage reading will be

9

2/23/2014

Wheatstone Bridge •

If the bridge is initially  balanced, the initial voltage reading V g should be zero. This  yields the following relationship  between the four resistances,

Application: Typical strain gauge resistances range from 30 Ω to 3 k Ω (unstressed). used in mechanical engineering research and measure the stresses generated by machinery. Aircraft component testing, linkages, and any other critical component of an airframe to measure stress.

10

2/23/2014

ABDULLAH IBNU AL-ABBAS “Bertukar fikiran tentang ilmu sebahagian daripada malam, lebih disukai daripada berbuat ibadah di malam hari” “Sesiapa yang memiliki empat perkara itu, dia beruntung iaitu benar, malu, bagus akhlak dan zuhud.”

Amplifiers   

The amplifier is the most important component in a measurement system. The ratio output/input is the gain, G of the amplifier. If the input voltage is v i and the output is v o, then  v o=G v i Inverting input

-

1 Output

NC Invert

+ Noninverting input

8

Noninvert V

V+ Output

-

11

2/23/2014

 Amplifiers 

 An Operational amplifier is a circuit that contain transistors, diodes, resistors and capacitors to form an amplification circuit.



There are several types of operational amplifiers:  Inverting & non-inverting  Differential amplifier   Voltage Follower  Summing amplifier  Comparator  Integrating amplifier  Differentiating amplifier

 Amplifiers

12

2/23/2014

Ideal Op-Amp 

Infinite voltage gain



Infinite input impedance



Zero output impedance



Zero input offset

Practical Op-Amp    

Very high voltage gain Very high input impedance Very low output impedance. Output voltage offset.

13

2/23/2014

 Voltage Follower 

Input signal is at the noninverting input.



Negative feedback 



Gain is 1



 V out =V in

Used to remove the high input impedance. The load will see a low input impedance(from the output of the amplifier).

Voltage Follower application The voltage follower is often used for the construction of buffers for logic circuits. The buffer is a single-input device which has a gain of 1, mirroring the input at the output. It has value for impedance matching and for isolation of the input and output.

 A  High output impedance

B Low input impedance

14

2/23/2014

Inverting Op-Amp    

Signal is applied to the inverting input Non-inverting input is grounded Negative feedback  Close loop gain: R

V A VCL

=

out V in

= −

R

f  1

Example: Calculate Voltage gain of the inverting Op-amp if the R1 = 20k Ω and Rf = 300kΩ Ans : -15

Non-Inverting Op-Amp    

Signal is applied to the non-inverting input Inverting input is grounded. Negative feedback  Close loop gain: V A VCL

=

out V in

=

  R    1 + f    R  1    

Example: Calculate Voltage gain of the non inverting op-amp . Given R1=150k Ω and Rf=30k Ω. Ans : 6

15

2/23/2014

 Application : Strain Gauge Half-Bridge Arrangement

Op amp used to amplify output from strain gauge

R +  ∆R  V ref 

Rf 

R 

+ V cc 

+

+

-

- V cc 

R 

+ V 0 

R -  ∆ R 

Rf 

Using KCL at the inverting and non-inverting terminals of the op amp we find that 

ε  ~

 __

V o = 2  ∆R(R f /R 2  )

Summing inverting Amplifier    V

Signals are applied to the inverting input. Non-inverting input is grounded. Negative feedback  out

=

  V  1 −R f   R   1

V +

R

2 2

   R  3   V

+

3

Example : Calculate the output voltage for the circuit if the R f = 200 KΩ , R1 = 10KΩ, R2=50KΩ , R3=15 KΩ, V1=V2=V3=0.8 V.

Find the output voltage of the following Summing Amplifier circuit. Ans : Vout= - 45 mV

16

2/23/2014

Summing non inverting Amplifier    V

Signals are applied to the non inverting input. Inverting input is grounded. Positive feedback  out

=

R

  V  1 f   R   1

V +

R

2

   R  3   V

+

2

3

Example : Calculate the output voltage for the circuit if the Rf = 200 KΩ , R1 = 10KΩ, R2=50KΩ , R3=15 KΩ, V1=V2=V3=0.8 V.

Differential Amplifier 

2 signal are applied.



Negative feedback  R V

out

=

R

(

2 V 1

2

−

V 1

)

17

2/23/2014

Integrating Amplifier 

Signals are applied to the inverting input.



Non-inverting input is grounded.



Negative feedback 



 V out =-(1/RC)∫ V in dt

Differentiating Amplifier 

Signals are applied to the inverting input.



Non-inverting input is grounded.



Negative feedback 

18

2/23/2014

Comparator 

When two inputs are equal, output is 0 V



NON- INVERTING input is greater than inverting input by more than a small fraction of volt then the output jumps to a steady positive saturation voltage.



INVERTING input greater than non-inverting input then output jumps to a steady negative saturation voltage. Inverting

Non - Inverting

19

2/23/2014

EXAMPLE APPLICATION:

Filters 



 A filter is used to remove undesirable frequency  information from a dynamic signal. Filter can be classified into the following: 

Low pass,



high pass,



 band pass,



notch pass

20

2/23/2014

Filter Characteristics

Filter Characteristics

21

2/23/2014

Filter Characteristics

Passive/ Active Filters 

Depending on the type of filter, we can define the following: 

f c= cut-off frequency 



f ch=high cut-off frequency 



f cl=low cut-off frequency 



f r=reject frequency 



Magnitude ratio, M(f)



Dynamic error, ∂(f)



Phase shift, φ(f)



 Attenuation, dB (decibels)

22

2/23/2014

Filters Design 

There are 2 main types of filters:  Passive filter: made of passive components such as resistors, capacitors and inductors.   Active filter, employing operational amplifier.



Passive filters may be realized either with:  Resistors-capacitors : These are RC filters, and they are the most used since they are easier and cheaper to  build.  Inductors-Capacitors . They are noted as LC filters, and they have better performances. The problems are: inductors are expensive, very difficult to "tailor" to exact values, and they require shielding of their electromagnetic field.

Passive Low-Pass Filter Design

 A low pass filter allows low frequencies to pass through the filter and blocks out high frequencies.

23

2/23/2014

Passive High-Pass Filter Design

 A high pass filter does the opposite of a low pass filter: blocks low frequencies and lets high frequencies pass through.

Passive Band-Pass Filter Design  A band pass filter is like a low pass and a high pass filter used in combination to isolate a group of frequencies to pass through while everything else gets cut out.

24

2/23/2014

Passive Notch-Pass Filter Design

 A band reject filter is the opposite of a band pass filter: a band of frequencies is blocked while everything else is let through.

Further Readings 1. Bolton, W., Mechatronics: Electronic Control Systems in Mechanical and Electrical Engineering  • Chapter 3  2. D. G. Alciatore and M. B. Histand, "Introduction to Mechatronics and Measurement Systems • Chapter 5 

25

2/23/2014

TAMAT

ABDULLAH BIN ABBAS:

“ Ilmu itu didapati dengan lidah yang gemar bertanya dan akal yang suka berfikir”

26