Effect of Integral Reset Action

Once again, sustained cycling occurs when the peak to valley is 200% of the size of the step change in setpoint. However, note that the peak-to-peak time period in the process variable is 24 min, that is, about twice as long, when the cycling occurs with too much reset. That is because the proportional gain, 

the integral time constant, 7), can be set equal to the response time for excellent response to a load change or twice the response time for minimum variability from a set-point change. 

The value of 7) can be set to about 2 times the response time of 13.0 min, that is, 26 min, for minimum variability to a setpoint change. For many combinations of K, K, DT, 7, and 7) for self-regulating control loops, a correlation was observed for minimum lAE, as shown in Equation 9.1. In this case, the optimum value of was found to be 4.08, and Kp was 1.0, so the calculated 7i, was 1.75 times the response time of 13 0 min, that is, 22.7 min. 

71 = integral time constant for controller (in minutes) for minimum lAE for setpoint changes 

Response time = elapsed time between step change in setpoint and first peak (in minutes) 

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