FIGURE 2.1 The purpose of linearization is to provide an output that varies linearly with some variable even if the sensor output does not. Curtis Johnson

FIGURE 2.1 The purpose of linearization is to provide an output that varies linearly with some variable even if the sensor output does not.

Curtis JohnsonProcess Control Instrumentation Technology, 8e]

Copyright ©2006 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458

All rights reserved.

FIGURE 2.2 The Thévenin equivalent circuit of a sensor allows easy visualization of how loading occurs.




FIGURE 2.3 If loading is ignored, serious errors can occur in expected outputs of circuits and gains of amplifiers.




FIGURE 2.4 The simple voltage divider can often be used to convert resistance variation into voltage variation.




FIGURE 2.5 The basic dc Wheatstone bridge.




FIGURE 2.6 When a galvanometer is used for a null detector, it is convenient to use the Thévenin equivalent circuit of the bridge.




FIGURE 2.7 For remote sensor applications, this compensation system is used to avoid errors from lead resistance.




FIGURE 2.8 The current balance bridge.




FIGURE 2.9 Using the basic Wheatstone bridge for potential measurement.




FIGURE 2.10 A general ac bridge circuit.




FIGURE 2.11 The ac bridge circuit and components for Example 2.10.




FIGURE 2.12 (a) Bridge off-null voltage is clearly nonlinear for large-scale changes in resistance. (b) However, for small ranges of resistance change, the off-null voltage is nearly linear.




FIGURE 2.13 Circuit for the low-pass RC filter.




FIGURE 2.14 Response of the low-pass RC filter as a function of the frequency ratio.




FIGURE 2.15 Circuit for the high-pass RC filter.




FIGURE 2.16 Response of the high-pass RC filter as a function of frequency ratio.




FIGURE 2.17 Cascaded high-pass RC filter for Example 2.13.




FIGURE 2.18 Analysis of loading for a high-pass RC filter in Example 2.14.




FIGURE 2.19 The response of a band-pass filter shows that high and low frequencies are rejected.




FIGURE 2.20 A band-pass RC filter can be made from cascaded high-pass and low-pass RC filters.




FIGURE 2.21 Band-pass response for the filter in Example 2.15.




FIGURE 2.22 Response of a band-reject, or notch, filter shows that a middle band of frequencies are rejected.




FIGURE 2.23 One form of a band-reject RC filter is the twin-T.




FIGURE 2.24 The twin-T rejection notch is very sharp for one set of components.




FIGURE 2.25 The schematic symbol and response of an op amp.




FIGURE 2.25 (continued) The schematic symbol and response of an op amp.




FIGURE 2.26 The op amp inverting amplifier.




FIGURE 2.27 Nonideal characteristics of an op amp include finite gain, finite impedance, and offsets.




FIGURE 2.27 (continued) Nonideal characteristics of an op amp include finite gain, finite impedance, and offsets.




FIGURE 2.28 Some op amps provide connections for an input offset compensation trimmer resistor.




FIGURE 2.29 Input offset can also be compensated using external connections and trimmer resistors.




FIGURE 2.30 The op amp voltage follower. This circuit has unity gain but very high input impedance.




FIGURE 2.31 The op amp summing amplifier.




FIGURE 2.32 The op amp circuit for Example 2.18.




FIGURE 2.33 A noninverting amplifier.




FIGURE 2.34 The basic differential amplifier configuration.




FIGURE 2.35 An instrumentation amplifier includes voltage followers for input isolation.




FIGURE 2.36 Solution for Example 2.20.




FIGURE 2.37 This instrumentation amplifier allows the gain to be changed using a single resistor.




FIGURE 2.38 Bridge for Example 2.21.




FIGURE 2.39 A voltage-to-current converter using an op amp.




FIGURE 2.40 A current-to-voltage converter using an op amp. Care must be taken that the current output capability of the op amp is not exceeded.




FIGURE 2.41 An integrator circuit using an op amp.




FIGURE 2.42 This circuit takes the time derivative of the input voltage.




FIGURE 2.43 A nonlinear amplifier uses a nonlinear feedback element.




FIGURE 2.44 A diode in the feedback as a nonlinear element produces a logarithmic amplifier.




FIGURE 2.45 Model for measurement and signal-conditioning objectives.




FIGURE 2.46 One possible solution to Example 2.24.




FIGURE 2.47 One possible solution for Example 2.25.




FIGURE 2.48 ac bridge for Problem 2.14.




FIGURE 2.49 Circuit for supplementary problems.




FIGURE 2.50 System for Problem S2.4.




FIGURE 2.51 Nonlinear amplifier using diodes for Problems S2.6 and S2.7.




FIGURE 2.52 Voltage versus pressure for Problem S2.7.




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FIGURE 2.1 The purpose of linearization is to provide an output that varies linearly with some variable even if the sensor output does not. Curtis Johnson