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I'm going to use Drum Level as the reference process here as this is what most are probably familiar with.
Also, for clarification, I have the FW Pressure constant, the Drum Level flatlining at 0mm, and the Steam Flow constant, therefore all is in equilibrium.
IMC Equation is:
Kc = (1/Kp)x(Tp/(Td + Tc))
Tn = Tp
Lambda Equation is:
Kc = Tn/(dL(Lambda + Td)^2)
Tn = Td + (2 x Lambda)
Lambda = 3 x Td
I do a manual step test on the FW Control Valve, and as expected the Drum Level starts to Integrate (rise) up. I collect the neccessary process data etc, etc.
I've now directly got:
* Td - Dead Time (sec)
* dL - Level Rate Of Change (mm/sec)
* dCV - Change in Control Valve Position (%)
But I don't have:
* Tp - Process Time Constant (sec)
* KP - Process Gain
* Tn - Controller Integral (sec)
* Kc - Controller Gain
So how can I implement IMC if these are unknown.
I know you can implement Lambda Tuning, but from what I've seen with this, you end up with a very sluggish system that responds quite poorly due to the low value of Kc (please don't comment here on 3 element control, as this is not apart of the discussion).
Am I missing something here, or have other people used different methods?
Personally I've used a mixture of ZN, common sense (CV must be full open/closed due to certain criteria, etc.) and the ol' tune by feel. At the end of the day I achieve the desired result of acceptable and stable drum level with good recovery (mainly due to correctly tuned Feedforwards).
Comments in all shapes and forms are graciously invited...
Also, for clarification, I have the FW Pressure constant, the Drum Level flatlining at 0mm, and the Steam Flow constant, therefore all is in equilibrium.
IMC Equation is:
Kc = (1/Kp)x(Tp/(Td + Tc))
Tn = Tp
Lambda Equation is:
Kc = Tn/(dL(Lambda + Td)^2)
Tn = Td + (2 x Lambda)
Lambda = 3 x Td
I do a manual step test on the FW Control Valve, and as expected the Drum Level starts to Integrate (rise) up. I collect the neccessary process data etc, etc.
I've now directly got:
* Td - Dead Time (sec)
* dL - Level Rate Of Change (mm/sec)
* dCV - Change in Control Valve Position (%)
But I don't have:
* Tp - Process Time Constant (sec)
* KP - Process Gain
* Tn - Controller Integral (sec)
* Kc - Controller Gain
So how can I implement IMC if these are unknown.
I know you can implement Lambda Tuning, but from what I've seen with this, you end up with a very sluggish system that responds quite poorly due to the low value of Kc (please don't comment here on 3 element control, as this is not apart of the discussion).
Am I missing something here, or have other people used different methods?
Personally I've used a mixture of ZN, common sense (CV must be full open/closed due to certain criteria, etc.) and the ol' tune by feel. At the end of the day I achieve the desired result of acceptable and stable drum level with good recovery (mainly due to correctly tuned Feedforwards).
Comments in all shapes and forms are graciously invited...
