chapter 9

FIGURE 9.1 Control of temperature by process control.

Curtis JohnsonProcess Control Instrumentation Technology, 8e]

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

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FIGURE 9.2 The error detector and controller.




FIGURE 9.3 Two-position controller action with neutral zone.




FIGURE 9.4 Figure for Example 9.4.




FIGURE 9.5 Three-position controller action.




FIGURE 9.6 Relationship between error and three-position controller action, including the effects of lag.




FIGURE 9.7 Single-speed floating controller as shown in: (a) single-speed controller action as the output rate of change to input error, and (b) an example of error and controller response.




FIGURE 9.8 Multiple-speed floating mode control action.




FIGURE 9.9 Single-speed floating-control action applied to a flow-control system.




FIGURE 9.10 The rate of controller output change has a strong effect on error recovery in a floating controller.




FIGURE 9.11 The proportional band of a proportional controller depends on the inverse of the gain.




FIGURE 9.12 An offset error must occur if a proportional controller requires a new zero-error output following a load change.




FIGURE 9.13 Level-control system for Example 9.6.




FIGURE 9.14 Integral mode controller action: (a) The rate of output change depends on error, and (b) an illustration of integral mode output and error.




FIGURE 9.15 Illustration of integral mode output and error, showing the effect of process and control lag.




FIGURE 9.16 The error can be zero but the rate of change very large.




FIGURE 9.17 Derivative mode controller action changes depending on the rate of error.




FIGURE 9.18 Proportional-integral (PI) action showing the reset action of the integral contribution. This example is for reverse action.




FIGURE 9.19 Overshoot and cycling often result when PI mode control is used in start-up of batch processes. The dashed lines show the proportional band.




FIGURE 9.20 Solution for Example 9.8.




FIGURE 9.21 Proportional-derivative (PD) action showing the offset error from the proportional mode. This example is for reverse action.




FIGURE 9.23 The three-mode controller action exhibits proportional, integral, and derivative action.




FIGURE 9.25 Figure for Problems 9.7 and 9.18.




FIGURE 9.26 Figure for Problems 9.12 to 9.15.




chapter 9

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