PID_ Valve control

[balabhi]

Hello,

This is my first time using the PID toolkit and I am attempting to regulate the valve by giving volume flow. I want to control the valves so that the program will open and close the valves as needed to reach the desired set point(Volume flow).  My main problem valve is taking either 0 or 10 as output(ie; Fully closed or fully open).  Any help would be appreciated.  I have attached what I have done so far.

Thanks

[RavensFan]

You posted your message to the tail end of an unrelated message thread.

If you want help, you need to start a new message thread with your question.  I have moved your message to a new thread for you.

Please read,

NI Community User Guidelines

Posting Basics and Tip

NI Community User Guidelines

[GerdW]

Hi balabhi,

My main problem valve is taking either 0 or 10 as output(ie; Fully closed or fully open). 

Does your valve only accept either 0V/10V or does your VI just output these two values?

On your VI:

- Why have you configured DAQAssistent to read 5 samples at 1Hz samplerate? This will take 5s - no PID control does like such delays!

- Why is there DAQAssistent3 with some "feedback voltage"?

- Why are you using default PID gains? Do they fit for your control loop?

- Why do you use DAQAssistent ExpressVIs at all? DAQmx functions are so easy to use and there is a huge library of example VIs!

[balabhi]

Hi GerdW,

Thanks for your reply.

Does your valve only accept either 0V/10V or does your VI just output these two values?

 -- VI just output either 0V/10V. Valve voltage is in the range of 0-10V.

Why is there DAQAssistent3 with some "feedback voltage"?

--To check the valve position. As VI just output either 0V/10V, I get the same feedback voltage.

Why are you using default PID gains? Do they fit for your control loop?

-- Yeah they do.

I am not familiar with DAQmx functions. Will be learning it soon.

Could you please tell me, What changes I should make in my program so that the output voltage ranges from 0-10V.

For example: If I give the volume flow/set point (400l/hr) the output of the PID should choose range from 0-10V. 

Thanks .

Regards,

Balabhi.

[GerdW]

Hi balabhi,

I suggest:

- don't use those big delays when reading new measurement data!

- rethink about using better PID gains!

[balabhi]

Hi ,

Even after changing the PID gains(as per Ziegler Nichloas Method) I am  not getting proper voltage signal. Output which comes from PID is either 0 or 10V(ie ; valve is either closing fully or opening fully).

what is the mistake in my VI?

Thanks.

[GerdW]

Hi balabhi,

(possible) errors:

- There is no VI, but just bad images…

- You don't like to use the Autocleanup tool

- You scale your input value by 150k: does that result in useful values?

- what is the allowed setpoint range?