Tuning Methods Based on Known Process Models

The principal Umitation to using these rules is that the true process parameters are often unknown. Steady-state gain K can be calculated from a process model, or determined from the steady-state results of a step test as Ac/Au, as shown in Fig. 8-28. The test will not be viable, however if the time constant of the process x is longer than a few minutes, since five time constants must elapse to approach a steady state within 1 percent, and unexpected disturbances may intervene. Estimated dead time 0 is the time from the step to the intercept of a 

TABLE 8-3 Tuning Rules Using Slope and Intercept 

8-28 If a steady state can be reached, gain K and time constant t can be estimated from a step response if not, use Xi instead. 

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Tuning Methods Based on Known Process Models. 8-14... 

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