Autotune (Relay) Tuning Method:
  1. Using a constant input, say uo, determine the corresponding steady state output, say yo.
  2. Next, change the setpoint to be yo.
  3. Switch the controller to relay mode and choose a small value for h. This will implement the following algorithm:



  5. Under this mode, the output should settle towards a limit cycle.



  7. From the plot, measure the amplitude of the output cycle, a. Using both a and h, the ultimate gain, Ku, can then be approximated by

  8. Ku = (4/p)(h/a)

  9. Using as an approximate for the ultimate gain Ku and ultimate period Pu (the period of the limit cycle in the plot above), apply the same prescribed values in Ziegler and Nichols method. ( Click here to go to Ziegler-Nichols method)


( Use the BACK button of your browser to return to a currently running PID tuning simulation, otherwise click here to initiate a PID tuning simulation.)

This page is maintained by Tomas B. Co ( Last revised 1/12/1999.

     Tomas B. Co
     Associate Professor
     Department of Chemical Engineering
     Michigan Technological University
     1400 Townsend Avenue
     Houghton, MI 49931-1295

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