Hi everyone

I am working on FATEK PID Module named "TPCTL" . The PID expression used is in digitalized form , the picture is also attached with post.
The Proportional Gain Kc is being used in Integral and as well as in Derivative part of PID which is confusing to me as why it is need to used Proportional Gain in other two parts of PID control as these parts have their own gain parameters?

 

Hi Faizanzaheer,
There are different PID structures. The one you have is called a standard PID (it's the most common one) : I find it pretty convenient. For example if your loop is too nervous (PV tends to cycle), one simple way to calm things down is to reduce proportional, integral and derivative in the same proportion : with a standard PID you just have to reduce Kc.
In a standard PID Kc should not be called proportional gain but actually controller gain since it is a multiplying factor of the three PID terms.
No matter the PID structure you have ; you just need to know which one you have.

 

Hi Faizanzaheer,
There are different PID structures. The one you have is called a standard PID (it's the most common one) : I find it pretty convenient. For example if your loop is too nervous (PV tends to cycle), one simple way to calm things down is to reduce proportional, integral and derivative in the same proportion : with a standard PID you just have to reduce Kc.
In a standard PID Kc should not be called proportional gain but actually controller gain since it is a multiplying factor of the three PID terms.
No matter the PID structure you have ; you just need to know which one you have.

Thank You for resolving my confusion.
and what about the factor Ts which is solution interval , how it will effect the PID when it is changed to 1 sec or to 2 sec ?

 

and what about the factor Ts which is solution interval , how it will effect the PID when it is changed to 1 sec or to 2 sec ?

It depends on the units of Ki. Ki would need to have units of 1/time or be an inverse time constant to be correct. Ki should be replaced by 1/Ti. This way the time units cancel out. Ki implies it is a gain and not a time constant. This is not a normal way of expressing a PID controller but then most industrial controller PIDs are written by people that have no idea what they are really doing and just copy something from someplace else.

You need to look at the units for the different terms. Each of the 3 terms for P I and D should have final units of %output.

 

I understand Ki is expressed in repeat per minute : it's the inverse of the integral time Ti (when this one is expressed in minute).
Ts is the controller cycle time which is also expressed in minute. If Ts is too long this may make your control loop become unstable. For a self regulating process Ts should be set roughly equal to 1/30th of the process settling time. For an integrating process such as in a level control loop Ts should not be greater than 1/20th of the tank residence time.