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# Chapter 9

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FIGURE 9.1 Control of temperature by process control.

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FIGURE 9.2 The error detector and controller.

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FIGURE 9.3 Two-position controller action with neutral zone.

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FIGURE 9.4 Figure for Example 9.4.

Curtis JohnsonProcess Control Instrumentation Technology, 8e]

FIGURE 9.5 Three-position controller action.

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

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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.

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FIGURE 9.8 Multiple-speed floating mode control action.

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

Curtis JohnsonProcess Control Instrumentation Technology, 8e]

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

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

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

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FIGURE 9.13 Level-control system for Example 9.6.

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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.

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

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

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

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

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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.

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FIGURE 9.20 Solution for Example 9.8.

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

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FIGURE 9.22 Solution for Example 9.9.

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

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FIGURE 9.24 Solution for Example 9.10.

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FIGURE 9.25 Figure for Problems 9.7 and 9.18.

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FIGURE 9.26 Figure for Problems 9.12 to 9.15.

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