What is PID 3

[Jigneshpadia2002]

Can anyone please explain me about the PID and its importance? I have very brief knowledge about it and what I know is PID helps to control the process but if some one can explain the elements of PID and how it works it will be very useful for me to understand and clarify my concept of PID and SCADA based Chromatography system.

Many Thanks in Advance

 

[Montemayor]

There are numerous reasons and justifications for a Piping and Instrumentation Diagram (P&ID). You'll find some in the following thread:
thread798-113006

I'm presuming that is what you mean by PID, and I hope it helps to give you a perspective on what it is used for and its importance.

 

[rbcoulter]

PID can mean the way Montemayor says or "Proportional, Integral, Derivative" which is a traditional algorithm for process controllers. A PID controller makes changes to defined output (e.g. valve position) based on the sum of the
errors (proportional, integral, & derivative) from setpoint. The proportional error is based on the current deviation from setpoint. The integral error is based on the history of the deviation. The derivative error is based on the rate of change of the deviation.

 

[Jigneshpadia2002]

Thanks rbcoulter !
I mean exactly what you told but this information is still bit difficult to get the complete idea about PID so if you can please elaborate on it for me.

Thanks a lot

 

[Guidoo]

There is so much information available on the Internet about PID control... Just do a Google search on say "PID proportional" and you find a lot. For example

http://www.expertune.com/tutor.html

 

[25362]

The link by Guidoo is a good tutorial. Definitions a bit different are:

In proportional control the amount of corrective action is proportional to the amount of error.

In derivative action the speed at which a correction is made depends on how fast the system error is increasing.

In integral control the control signal changes at a rate proportional to the error signal.

In P+I+D control, as rbcoulter said, the control signal is a linear combination of the error signal, its integral and its derivative.

 

[rbcoulter]

The subject is too complicated to go into detail here.
The link provided by Guidoo appears to be a good place to start.

 

[MortenA]

PID control is very basic in process control. If you dont know about this (and wants to call yourself an instrumentation engineer) then you need to get back to the studyroom!

Best regards

Morten

 

[Lblopez]

Hello,
I dont Know if you still need the information about PID
A simple way to understand is: The PID controller is the controller used by excellence to mantain a variable like temperature and concentration in a value that you fixed or your process fixed (set-point).

Everybody here said you the mean of P, I and D and if you dont have control process knowledges you cant understand it.

In a chromatography system the PID controller maybe mantain some reference concentration (if have it)or the temperature in the surface of solid (C Gas-Solid), in the entrance of analite, or any site of equipment that the temperature must be fixed in specific value.

 

[jsummerfield]

The PID algorithm is normally applied to a continuous process. Other issues exist if you are using a 4-20 mA output from a chromatograph to adjust a control valve or other process controller. The chromatograph has a batch cycle with a new analysis each cycle. The output may change to the new value once - and remain at that level until the next cycle. There are lots of ways to skin a cat. If you are limited to using a single 4-20 mA output or a serial link for the output data to a PID controller, assure that the PID scan is equal to the chromatograph cycle or one of the other techniques for such control.

John