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: