## Cohen Coon

Cohen Coon Tuning Method

1. Under Manual mode, wait until the process is at steady state.

2. Next, introduce a step change in the input.

3. Based on the output, obtain an approximate first order process with a time constant t delayed by tDEL units from when the input step was introduced.

The values of t and tDEL can be obtained by first recording the following time instances:

t0 = time when input step was initiated

t2 = time when half point occurs

t3 = time when 63.2% point occurs

4. From the measurements based on the step test: t0, t2, t3, A and B, evaluate the following process parameters:

t1 = (t2 – ln(2) t3)/(1 – ln(2))

t = t3 – t1

tDEL = t1 – t0

K = B/A

5. Based on the parameters K, t and tDEL, the following formulas prescribe the controller parameters Kc, tI and tD:

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