PID control

[chattarbir]

Dear Dr Imad

You asssumed all correctly. i shall try your suggestion and let you know how it helps.

mr ben I will upload the graphics of both cases as soon as i get them

Thanks gentle men for replying

regards

chattarbir singh

[chattarbir]

Dear Sir

I have tried your suggestions. I got the values but strange thing is my control works in opposite direction.

You have any suggestions.

regards

chattarbir singh

[Dr._Imad]

what do you mean by "opposite direction" ?

do you mean if you increase the voltage, the flow decreases (when you expect it to increase)?  If so, then the proportiional gain should be set negative (<0)

you may want to explain more.

[chattarbir]

Dear Dr. Imad

Well I made the proportional gain negative and now it resonably working good.

 But i have one argument and that is how will i justify the negative value of proportional gain . i have never seen or read about it. More over in my discussion with my collegues i had no argument to convince that this negative value is indeed right way.

Hope you can bail me out this time too

Regards

chattarbir 

[Dr._Imad]

In traditional control systems, if you increase the voltage, then you should expect the output (flow, pressure, etc) to increase.  In this case, the proportional case is positive.

If increasing the voltage decreases the output, then you have what is called a reverse acting  system, and the prop gain has to be negative.  The theory is clear and you find it in text books.

check this ni link

How Do I Implement a Reverse Acting Controller with the PID Control Toolset?

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