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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 t_DEL units from when the input step was introduced.


 

 

The values of t and t_DEL 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

t_DEL = t₁ - t₀

K = B/A




5. Based on the parameters K, t and t_DEL, the following formulas prescribe the controller parameters K_c, t_I and t_D:

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