EKT314/4 - Electronic Instrumentation 2 REFERENCE BOOK FOR
ANALOG SIGNAL CONDITIONING
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3 Analog Signal Conditioning IntroductionPassive Circuit
Operational Amplifier (OP AMP) OPAMP circuits in Instrumentatio n
Design Guidelines Principles
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EKT314/4 - Electronic Instrumentation 5 1.Explain the purpose
of analog signal conditioning. 2.Design a Wheatstone bridge circuit
to convert resistance change to voltage change. 3.Design RC
low-pass and high pass filter circuits to eliminate unwanted
signals. 4.Draw the schematics of four common op amp circuits and
provide the transfer functions. 5.Explain the operation of an
instrumentation amplifier and draw its schematic. 6.Design an
analog signal-conditioning system to convert an input range of
voltages to some desired output range of voltage. 7.Design analog
signal conditioning so that some range of resistance variations is
converted into a desired range of voltage variation.
Objectives
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EKT314/4 - Electronic Instrumentation 6 Signal Conditioning
-Operations performed on signals to convert them to a form suitable
for interfacing with other elements in the process-control loop.
This chapter only concern about analog conversions. -Effect of the
SC is described by the term transfer function.
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7 Analog Signal Conditioning IntroductionPassive Circuit
Operational Amplifier (OP AMP) OPAMP circuits in Instrumentatio n
Design Guidelines Principles
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8 Analog Signal Conditioning PrinciplesSignal Level and Bias
Changes Linearizatio n ConversionFiltering & Impedance matching
Concept of Loading
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EKT314/4 - Electronic Instrumentation 9 Signal Level and Bias
Changes Adjusting the level (magnitude) and bias (zero values) of
some voltage representing a process variable.
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Curtis Johnson Process Control Instrumentation Technology, 8e]
Linearizatio n The purpose of linearization is to provide an output
that varies linearly with some variable even if the sensor output
does not.
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EKT314/4 - Electronic Instrumentation 11 Convert one type of
electrical variation into another. -Signal Transmission (Voltage to
current, Current to Voltage converter) -Digital Interface (ADC
requires 0-5V input) Conversion
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EKT314/4 - Electronic Instrumentation 12 Filtering &
Impedance matching -Filtering-Eliminate unwanted signals in the
process-control loop -Impedance matching- transducer internal
impedance or line impedance can cause error in measurement of a
dynamic variable.
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EKT314/4 - Electronic Instrumentation 13 Concept of Loading
Thvenin's theorem for linear electrical networks states that any
combination of voltage sources, current sources, and resistors with
two terminals is electrically equivalent to a single voltage source
V and a single series resistor R. Concern -loading of one circuit
by another.
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EKT314/4 - Electronic Instrumentation 15
Slide 16
Curtis Johnson Process Control Instrumentation Technology, 8e]
Copyright 2006 by Pearson Education, Inc. Upper Saddle River, New
Jersey 07458 All rights reserved. Example: An amplifier outputs a
voltage that is 10 times the voltage on its input terminal. It has
an input resistance of 10 k. A sensor outputs a voltage
proportional to temperature with a transfer function of 20mV/ C.
The sensor has an output resistance of 5.0 k. If the temperature is
50 C, find the amplifier output.
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EKT314/4 - Electronic Instrumentation 17
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18 Analog Signal Conditioning IntroductionPassive Circuit
Operational Amplifier (OP AMP) OPAMP circuits in Instrumentatio n
Design Guidelines Principles
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19 Passive Circuits Bridge Circuits RC FiltersDivider circuits
Analog Signal Conditioning
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Copyright 2006 by Pearson Education, Inc. Upper Saddle River, New
Jersey 07458 All rights reserved. Divider circuits
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EKT314/4 - Electronic Instrumentation 21
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EKT314/4 - Electronic Instrumentation 23 Bridge Circuits Bridge
circuits are used to convert impedance variations into voltage
variations
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Jersey 07458 All rights reserved.
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EKT314/4 - Electronic Instrumentation 25 if Zero difference and
zero voltage across the detector
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EKT314/4 - Electronic Instrumentation 26
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EKT314/4 - Electronic Instrumentation 27 *-ve result means that
Vb larger Va.
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EKT314/4 - Electronic Instrumentation 29
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EKT314/4 - Electronic Instrumentation 31
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Curtis Johnson Process Control Instrumentation Technology, 8e]
Copyright 2006 by Pearson Education, Inc. Upper Saddle River, New
Jersey 07458 All rights reserved. LEAD COMPENSATION -When bridge
circuit may be located at considerable distance from the sensor
whose resistance changes are to be measured. -Problem many effect
that change the resistance. -any changes in lead resistance are
introduced equally into both arms of the bridge circuit, thus
causing no effective change in bridge offset
Slide 33
Curtis Johnson Process Control Instrumentation Technology, 8e]
Copyright 2006 by Pearson Education, Inc. Upper Saddle River, New
Jersey 07458 All rights reserved. CURRENT BALANCE BRIDGE -this
method uses a current to null the bridge
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EKT314/4 - Electronic Instrumentation 34
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EKT314/4 - Electronic Instrumentation 35 -A bridge circuit is
useful for measuring small potentials at very high impedance using
either a Wheatstone bridge or current balance bridge. -performs by
placing the potential to be measured in series with the
detector.
Slide 36
Curtis Johnson Process Control Instrumentation Technology, 8e]
Copyright 2006 by Pearson Education, Inc. Upper Saddle River, New
Jersey 07458 All rights reserved. Using Current balance bridge
Using Wheatstone bridge
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EKT314/4 - Electronic Instrumentation 37
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EKT314/4 - Electronic Instrumentation 39 ac bridges
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Curtis Johnson Process Control Instrumentation Technology, 8e]
Copyright 2006 by Pearson Education, Inc. Upper Saddle River, New
Jersey 07458 All rights reserved. ac bridges
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EKT314/4 - Electronic Instrumentation 42
Slide 43
Curtis Johnson Process Control Instrumentation Technology, 8e]
Copyright 2006 by Pearson Education, Inc. Upper Saddle River, New
Jersey 07458 All rights reserved. Primary application of bridge
circuits -To Convert variations of resistance into Variations of
voltage If the range of resistance variation is Small and centered
about the null value Then then nonlinearity of voltage Resistance
is small.
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EKT314/4 - Electronic Instrumentation 44 RC Filters To
eliminate unwanted noise signals from measurements, it is often
necessary to use circuits that block certain frequencies or bands
of frequencies.
Slide 45
Curtis Johnson Process Control Instrumentation Technology, 8e]
Copyright 2006 by Pearson Education, Inc. Upper Saddle River, New
Jersey 07458 All rights reserved. Low-pass RC Filter -It blocks
high frequencies and passes low frequencies.
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EKT314/4 - Electronic Instrumentation 47 Critical Frequency=fc
-ratio of the output to the input voltage is approximately
0.707
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EKT314/4 - Electronic Instrumentation 48 Find the critical
frequency that will satisfy the design criteria.
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Curtis Johnson Process Control Instrumentation Technology, 8e]
Copyright 2006 by Pearson Education, Inc. Upper Saddle River, New
Jersey 07458 All rights reserved. High-Pass Filter -Passes High
frequencies -Blocks low frequencies
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EKT314/4 - Electronic Instrumentation 53
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EKT314/4 - Electronic Instrumentation 54 Filter that blocks
frequencies below a low limit and above a high limit while passing
frequencies between the limits.
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Slide 56
Curtis Johnson Process Control Instrumentation Technology, 8e]
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Jersey 07458 All rights reserved. Good passband filter. -critical
frequencies be as far as possible -resistor ratio below 0.01
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EKT314/4 - Electronic Instrumentation 58
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EKT314/4 - Electronic Instrumentation 59 -Filter that blocks
specific range of frequencies. -Difficult to design using RC
combinations, possible using inductor and capacitors -Most success
using active circuits.
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Curtis Johnson Process Control Instrumentation Technology, 8e]
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65 Analog Signal Conditioning IntroductionPassive Circuit
Operational Amplifier (OP AMP) OPAMP circuits in Instrumentatio n
Design Guidelines Principles
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66 Operational Amplifier Specificatio n Characteristics Analog
Signal Conditioning
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Curtis Johnson Process Control Instrumentation Technology, 8e]
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Curtis Johnson Process Control Instrumentation Technology, 8e]
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Curtis Johnson Process Control Instrumentation Technology, 8e]
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Curtis Johnson Process Control Instrumentation Technology, 8e]
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Curtis Johnson Process Control Instrumentation Technology, 8e]
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Curtis Johnson Process Control Instrumentation Technology, 8e]
Copyright 2006 by Pearson Education, Inc. Upper Saddle River, New
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74 Analog Signal Conditioning IntroductionPassive Circuit
Operational Amplifier (OP AMP) OPAMP circuits in Instrumentatio n
Design Guidelines Principles
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75 OpAmp Circuit in Instrumentatio n Inverting Amplifier
Voltage Follower Non Inverting Amplifier Differential
Instrumentatio n Amplifier Current to Voltage Converter Voltage to
Current Converter IntegratorDifferentiatorLinearization
Slide 76
Curtis Johnson Process Control Instrumentation Technology, 8e]
Copyright 2006 by Pearson Education, Inc. Upper Saddle River, New
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Curtis Johnson Process Control Instrumentation Technology, 8e]
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EKT314/4 - Electronic Instrumentation 81
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Curtis Johnson Process Control Instrumentation Technology, 8e]
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89 Analog Signal Conditioning IntroductionPassive Circuit
Operational Amplifier (OP AMP) OPAMP circuits in Instrumentatio n
Design Guidelines Principles
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90 Design Guideline ParameterOutput Impedance Range Input
Impedance Analog Signal Conditioning
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94 Analog Signal Conditioning IntroductionPassive Circuit
Operational Amplifier (OP AMP) OPAMP circuits in Instrumentatio n
Design Guidelines Principles
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