Ziegler-Nichols Z-N Open-Loop Tuning Rules of Thumb

2 Ziegler-Nichols (Z-N) Open-Loop Tuning Rules of Thumb 

Ziegler and Nichols presented an open-loop test method in their classic paper on tuning control loops. The method consists of starting with the control loop at steady state, putting the controller in manual output so that there is no feedback response from any change in the process variable, and introducing a step change in the controller output (valve position). Then the results are used to characterize the process response by an apparent 

The open-loop process gain, K, for a self-regulating process response is calculated from Equation 10.1. 

The process variable moved from 50% to 60% at steady state for an open-loop step change in controller output from 50% to 

The maximum process response rate, MPRR, is calculated from Equation 10.2. 

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