PID Troubles on a Flow controller???

[GenU1Chevy]

Hello,

I'm having trouble using PID control on an flow valve that requires a 0-12VDC power source.  My setup includes an Agilent 34970A with a mulitfunctional module to output power to a Kepco power supply which ouputs power to the flow controller.  The only way I can get PID to work is if I use a very small Gain such as (0.2), an Integral Time of (-.49) and a Derivative Time of (.005). It seems to dial in the flow meter within 2-3 minutes but it doesn’t seem right to put a negative value in for the Integral Time though??   I'm wondering if it has something to do with the hysteresis of the flow meter. Have you guys heard of anything like this happening with PID on a control valve?  Please let me know.

Thanks,  Jeff

Flow controller manf:  Teknocraft~Standard proportional control valve.

http://www.teknocraft.com/pdfs/proporvalve1.pdf

[Nate.H]

Dear Jeff,

I agree that a negative value for the integral time does not make much sense. I don't think this would result from the hysteresis of the flow meter, but then again, I don't have much experience with flow meters. Does your system behave as expected when just performing proportional control? I would get the system tuned using proportional control only, then add in the integral gain and finally the derivative gain. You could also follow a tuning method such as the Ziegler-Nichols Method to see if that would give you valid and more sensible gains for the system.

Please let me know how it goes in trying the above suggestions.

Best Regards,

~Nate

[siva0182]

HI i would also like to use labview to control a solenoid valve using a HP data acquistion system (HP 34970A)+ multifunctional module.

Is it possible to do temperature measurement also using multifunctional module?

Are the drivers common for all modules?

Is it possible to read data from one module and set the output of a multifunctional module accordingly?

[siva0182]

Alternatively Is it possible to send an output signal from labview to a digital to analog card/cable and then suitably control a solenoid valve.?

[Mathan]

search

[siva0182]

Thanks for that link.I did search thro the results ..but most of them use some kind of DAQ card or so.
I am more interested in using a multifunction module or a digital to analog cable..

regards
Sivanand Somasundaram

[muks]

Hi sivanand somasundaram,
                                               Have you checked this

[RT4CY · Accepted solution]

Hello,

The driver for the HP 34970A can be found in our Instrument Driver Network at www.ni.com/idnet.  Here is the link for the driver.  In addition to the forum post linked by muks, check out the following Developer Zone.

NI Developer Zone Tutorial: Complete resources for a PID control system with NI M Series devices

FYI, you will communicate with the HP 34970A via GPIB or Serial communication.  Thus, the underlying driver will be either 488.2 or VISA (respectively).  If you decide to go with a NI M-Series device, the driver used will be NI-DAQmx.

[shanky1023]

Hi

I am trying to write a simple code on Having a Loop control on a flowmeter. I wrote 2 codes one involving a P control and one Involving a Differnce in the set Point to the Actual output.

The idea is to control a flowmeter based on the pressure of flow . The Pressure measurement gives a Voltage output and the valve need a Current input so i need to control flow using desired Voltage output. But my code with the P control doesn not function as desired. ANd the code which uses just a differnce in a loop seems to work fine but for the fact that it never touches the desired value . it keeps oscilatting around the desired set point.

Could anyone help me set right the P Control ?

[GenU1Chevy]

Hi shanky1023 ,

Do you have the PID toolkit?  It might make it easier for you to write the code.  I don't have your subvi's or DAQmx vi's but the PID toolkit has all the PID subvi's to control a flowmeter.   I would look into that.  Let me know if you have any questions.