Chap 3 Signal Conditioning Circuit

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1

MECHATRONIC SYSTEM

MECHATRONIC SYSTEM

DESIGN

DESIGN

SIGNAL CONDITIONING 

SIGNAL CONDITIONING 

Outlines

Outlines

•

•

Conditioning Circuits

Conditioning Circuits

•

•

Circuits Elements

Circuits Elements

•

•

Power Supply

Power Supply

•

•

DC Voltage Divider

DC Voltage Divider

•

•

AC Voltage Divider

AC Voltage Divider

•

•

Wheatstone Bridge

Wheatstone Bridge

•

•

Operational Amplifiers

Operational Amplifiers

•

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2

Introduction

Introduction

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Circuits Elements

Circuits Elements

Circuits Elements

Circuits Elements

Power supply 



 Voltage divider/ Wheatstone bridge



 Amplifiers



Filters



DAC/ ADC

Power Supply 



Battery 

  Advantages:

 Least expensive

 Constant voltage

 Large current flow.

 Disadvantages:

  Voltage decay with time under load

 Replaced when dead

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Zener Diode

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

  As long as V _s>V _zin reverse bias, the output voltage V _o= V _z

Vs Vz

Power Supply 

  We could also use the AC line power supply.

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

Power Supply 

Power Supply



The rectifier converts the low AC voltage

to a varying DC voltage.

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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)..

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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.

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Voltage Divider



Q: What happens when R 

and R 

is changed by 

R 

and  R  

? What is the expression for  V 

?



Q: What happens when Z

and Z

is changed by 

 Z

a n d  Z

? What is the expression for  V 

?

 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.,

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 Wheatstone Bridge

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

The voltage gage reading V _gcan then be obtained from,

Wheatstone Bridge

•

Now suppose that all

resistances can change during

the measurement.

•

The corresponding change in

voltage reading will be

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Wheatstone Bridge

•

If the bridge is initially

 balanced, the initial voltage

reading

V 

should be zero. This

 yields the following relationship

 between the four resistances,

Application:

Typical strain gauge resistances range from 30Ω to 3 kΩ (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.

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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 

and the output is v 

, then

 v 

=

 v 

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 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

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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.

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 Voltage Follower



Input signal is at the

non-inverting input.



Negative feedback 



Gain is 1



 V 

=V 

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. B Low input impedance  A  High output impedance

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Inverting Op-Amp

 Signal is applied to the inverting input

 Non-inverting input is grounded

 Negative feedback 

 Close loop gain:

1 R f  R in V out V AVCL = = − Example:

Calculate Voltage gain of the inverting

Op-amp if the R1 = 20kΩ 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:

            + = = 1 R f  R 1 in V out V AVCL Example:

Calculate Voltage gain of the non inverting op-amp . Given R1=150kΩand Rf=30kΩ. Ans : 6

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 Application : Strain Gauge

Half-Bridge Arrangement

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  ) R + ∆_R  R_f  + - ₊ V ₀   __ + V _cc  - V _cc  -+ R_f  V _{ref  R}  R -  ∆_R  R 

Op amp used to amplify output from strain gauge

Summing inverting Amplifier

 Signals are applied to the inverting input.

 Non-inverting input is grounded.

 Negative feedback 

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.

Find the output voltage of the following Summing Amplifier circuit.

Ans : Vout= - 45 mV             + + − = 3 R 3 V 2 R 2 V 1 R 1 V f  R out V

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Summing non inverting Amplifier



Signals are applied to the non inverting input.



Inverting input is grounded.



Positive feedback 

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.             + + = 3 R 3 V 2 R 2 V 1 R 1 V f  R out V

Differential Amplifier



2 signal are applied.



Negative feedback 

(

)

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Integrating Amplifier

 Signals are applied to the inverting input.

 Non-inverting input is grounded.

 Negative feedback 

  V _out=-(1/RC)∫ V _indt

Differentiating Amplifier



Signals are applied to the inverting input.



Non-inverting input is grounded.

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Comparator

Inverting

Non - Inverting

 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.

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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,

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Filter Characteristics

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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)

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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.

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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.

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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

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TAMAT

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