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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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Curtis Johnson Process Control Instrumentation Technology, 8e] Copyright 2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved.

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EKT314/4 - Electronic Instrumentation 15

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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. 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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Curtis Johnson Process Control Instrumentation Technology, 8e] 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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Curtis Johnson Process Control Instrumentation Technology, 8e] Copyright 2006 by Pearson Education, Inc. Upper Saddle River, New 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 27 *-ve result means that Vb larger Va.

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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.

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EKT314/4 - Electronic Instrumentation 29

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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

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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. 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.

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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. Using Current balance bridge Using Wheatstone bridge

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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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Curtis Johnson Process Control Instrumentation Technology, 8e] Copyright 2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved.

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EKT314/4 - Electronic Instrumentation 42

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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. 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.

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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. Low-pass RC Filter -It blocks high frequencies and passes low frequencies.

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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.

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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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Curtis Johnson Process Control Instrumentation Technology, 8e] Copyright 2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved.

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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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Curtis Johnson Process Control Instrumentation Technology, 8e] Copyright 2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved.

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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. Good passband filter. -critical frequencies be as far as possible -resistor ratio below 0.01

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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.

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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] Copyright 2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved.

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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.

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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.

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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] Copyright 2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved.

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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.

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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.

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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.

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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.

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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.

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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.

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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

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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 impedance Low impedance

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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.

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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.

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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.

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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.

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EKT314/4 - Electronic Instrumentation 81

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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.

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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.

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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.

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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.

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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.

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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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Curtis Johnson Process Control Instrumentation Technology, 8e] Copyright 2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved.

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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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Curtis Johnson Process Control Instrumentation Technology, 8e] Copyright 2006 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved.

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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.