PID control of proportional valve control suggestions

[newbieeng]

Hi everyone. I am starting a new big project whose first step is controlling four proportional gas valves with recpect to pressure feedback from a combustion chamber for gas filling process. We have four gas lines and it is desired to send four different gases through the chamber sequentially. The close time for each valve is determined by the pressure measurement inside the combustion chamber. For instance, firstly, we let the nitrogen gas flows to the chamber, and the pressure inside the of it reaches 5 bars, we closed the nitrogen valve, and open the argon gas valve, and hold it opened until the pressure is reached at 15 bars inside the chamber and so on.

Before, I made some projects via Labview, however, I have never done anything about PID control of valves or etc. The projects that I did includes basic control methds like on-off controls. So where can I start this project? Do I have to use PID library of labview and PWM for signal controlling? Can I do it by use of state machine or another design patterns (which one is the best)?

Valve controls: Bürkert 8605 (4-20 mA signal)

Daq: NI USB X 6343

[qzerror]

Sounds like fun.  A state machine would be a good way to go, especially since this appears to be a control sequence.  You may not need PID control if you are just going up to a set pressure and close the valve.  If your timing isn't critical, you can probably help with the accuracy if you regulate your input pressures to be just above your target so that you don't have to be controlling this within ms.  Otherwise, you could just use a proportional control without bothering with the PID library (e.g. 0-10V signal = gain * (setpoint - target)).

A related issue is that you need to convert your 0-10VDC signal to 4-20 mA, which is usually done with a converter, see this thread: http://forums.ni.com/t5/Signal-Conditioning/converting-0-10VDC-to-4-20mA/td-p/252776.  The cheapness of the converter you can get away with depends on your timing requirements.

[newbieeng]

Thanks for advicesqzerror.

Timing is important, since I will not only determine on-off timings of valves but also determine the proportinal opennings of them to control the pressure inside the chamber proportionally. Initially I will try to use software timing then I may change it to hardware timing.

NI USB x 6343 has 4 analog ampera output channels on it as far as I remember, but in the future I will need more ampera AO, hence converting volt AO to ampera AO will be necessary. I could not open the link about that subject (pops up error: "An invalid set of parameters has been specified in the url."), could you resend it to me please?

[GerdW]

Hi egemen,

remove the trailing dot from the link…

[newbieeng]

Hi GerdW, thank you. I have not seen this tiny guy