Page 64 - Instrumentation and Measurement
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FIGURE 4.18 PI control.
The combination of integral mode with proportional mode has one great advantage over the
proportional mode alone: the steady state error can be eliminated. This is because the integral part of
the control can provide a controller output even when the error is zero. The controller output is the
sum of the area all the way back to time t = 0 and thus even when the error has become zero, the
controller will give an output due to previous errors and can be used to maintain that condition. Figure
4.19 illustrates this.
FIGURE 4.19 Controller output when error becomes zero.
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