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Abdul Aziz Ishak, Dept. of Chemical Engineeering, Universiti Teknologi MARA, MALAYSIA
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Process plants

based on Cohen-Coon's tuning rule

1. Draw a tangent line at the steepest point of an open loop response curve
2. Estimate the dead time, Td.
3. Estimate the time constant, Tc, as shown in the figure above.
4. Calculate the uncontrolability parameter as defined below.

5. Select the controller mode i.e. P only, PI or PID
6. Calculate the PIDs based on the following:

For P only control


For PI control


For PID control


Note: RR is the process rate per controller output as defined in "Optimum PID calculation for SR and NSR process".

TEST YOURSELF: Compare the result between Cohen-Coon and Zieglar-Nichols. Use the following data.
16 October 99 / updated: 15 Aug. 2001