# Learning about PID



## drsparky (Nov 13, 2008)

I am just happy this thread was not about Pelvic Inflammatory Disease.


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## IMM_Doctor (Mar 24, 2009)

*PID - One Place to Start*



petek57 said:


> Where would be the best place to get started to learn Proportional Integral Derivative control?
> 
> I found the Wikipedia linkhttp://en.wikipedia.org/wiki/Proportional-Integral-Derivative_controller.
> 
> I would like to have some examples and perhaps just some basic stuff so that I can carry on an intelligent conversation and perhaps even begin dabbling.


The best place to start may be your PLC/PAC vendor. The reason I say this, is some PLC's put thier own litte twist on the the PID.

Some use Dependent Gains, some use Independent Gains. Some have a Proportial Gain, Some use a Proportional Band (Inverse methods). Some use Integral where it is "repeats per t" (time), some use "time between repeats". Some have D calculated on rate of Pv change, some have D calculated on rate of Cv change.

Again, it is best to study the tools that you plan on using.

A laymen's explanation of PID - "Like the Cruise Control of an Automobile".

Some basic terms...
Setpoint = User entered desired value (speed, rate, level, pressure, temperature) Example - MPH Miles Per Hour, how fast do you want your car to be traveling.

Process Variable Pv. Speedometer - How Fast are we going right now, actual speed.

ERROR = Setpoint-Pv = Error

Control Variable Cv = This is typicaly the output of the PID. Typically the greater the Error, the greater the Cv. How hard to push on the GAS pedal to reduce the error.

LAG Time. The time between a change in Cv to actually seeing a result in the Pv. Some processes like hydraulic pressure control have very little lag, and can be tuned aggressively. Some processes like electric heating may have an excessive lage time, and loops must be de-tuned to prevent excessive overshoot, and severe oscillations.


Also Google Ziegler Nichols. They have a lot of insightful PID knowledge to share with you.


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## InControl (Mar 20, 2007)

petek57 said:


> I would like to have some examples and perhaps just some basic stuff so that I can carry on an intelligent conversation and perhaps even begin dabbling.


This statement throws up some red flags for me. If i wanted to 'dabble' in plumbing, would I ask for basic 'stuff'? No, I would research on the WWW and ask specific questions. 

If your going to do something, do it right! For PID control, I would recommend HERE.


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## wildleg (Apr 12, 2009)

petek57 said:


> Where would be the best place to get started to learn about Erectile Dysfunction?
> 
> .


Sorry, I don't know anything about it.


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## petek57 (Mar 3, 2009)

Good stuff exactly what I was looking for. What is PAC?


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## petek57 (Mar 3, 2009)

Good link. Wanting to expand my horizons


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