Pressure Control Using Stepper Motor

[Hyperbaric_Engineer]

Hello Everyone,

I have  stepper motor based control valves (with internal motion controller). They need an open/close signal and a separate speed signal that determines the speed of opening or closing.  The open/close signal is 0 vdc for close and 12 vdc for open.  The speed signal is 0 to 2.5 vdc.  0 vdc is zero speed and 2.5 vdc is maximum speed. 

Question is, can I use a PID loop to control the pressure of a vessel? The user will dial a set point, and the PID loop will control the speed of the valve opening as long as Setpoint > Process. When the PID loop output reduces (because process > setpoint) I will turn the valve in the reverse direction (closing), however, I may end up closing the valve a bit too fast since I'm using the speed of opening when it's beginning to decline.

Am I doing the correct thing or is there another way?

[Blokk]

It may work, but probably you also need to apply a correct deadband to reduce the frequency of the activation of your output.

May I ask, is it a development of a new pressure control at a company, or just a hobby project? There are many very good off-the-shelf pressure controllers for many different applications. If you consider your dev time+your cost, maybe in the end it is just more cost effective to buy a device from a company... But of course if this is for learning/hobby project, it is a different story 🙂

[msmeulers]

hello,

you can use the PID also to generate a negative output, so let it run from -2.5 to 2.5. If the output of the PID becomes negative you know that the valve needs to close (open close signal = 0) and just make the output absolute. 

[Hyperbaric_Engineer]

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@Blokk wrote:

It may work, but probably you also need to apply a correct deadband to reduce the frequency of the activation of your output.

May I ask, is it a development of a new pressure control at a company, or just a hobby project? There are many very good off-the-shelf pressure controllers for many different applications. If you consider your dev time+your cost, maybe in the end it is just more cost effective to buy a device from a company... But of course if this is for learning/hobby project, it is a different story 🙂

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Thanks for the input Blokk.

This project is for a job and one of the user requirements is to have labview based control systems. I am just trying to get my head around the controls, once I've figured out it should be fairly quick.

[Hyperbaric_Engineer]

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@msmeulers wrote:

hello,

you can use the PID also to generate a negative output, so let it run from -2.5 to 2.5. If the output of the PID becomes negative you know that the valve needs to close (open close signal = 0) and just make the output absolute. 

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Very clever! This might just work out really well. Will have to put it to the test. Is it possible to make the PID start at 0 instead of -2.5? I should maybe do it programmatically.

[msmeulers]

Hello,

I'm guessing you have the same chal;lange as we had with the piston project over here. When the controller starts, you don't want it to move until the user enters a new setpoint.

Your PID controller will start (after a reinitialize) with your current setpoint - process value * Kc, so it is really dependant from those values. WIth the piston project the PID controller is always controlling the piston. So when I initialize the controller I just make currens setpoint equal to the process value, so 0 * Kc is always 0.  

Good luck!

Martijn

[GerdW]

Hi Hyperbaric,

Will have to put it to the test. Is it possible to make the PID start at 0 instead of -2.5? I should maybe do it programmatically.

 The (Advanced)PID function has a "manual" input. And when switching to automatic mode it will "bumpless" move from manual setting to setpoint setting…

Easy answer: provide a "manual" value have the PID output in the very same range as is needed to have a setpoint of zero. Use the concept as has been mentioned in the post before by Martijn!

[hemnath]

Hi,

I'm new here. I am also designing a pressure controller. But stucked. Need some help to develop it.

Which stepper motor based control valves should i use?

It could be helpful for me.

Thanks and Regards,

Hemnath.D

[GerdW]

Hi Hemnath,

designing a pressure controller. But stucked

Where did you stuck?

Which stepper motor based control valves should i use?

This isn't LabVIEW related at all!

Why do you insist on stepper motor based valves? Did you look for other valves?

There are pressure control valves, driven by current or PWM.

There are pressure control valves with included controllers, driven by voltage signal…

What is your setup? What have you considered until now?