propotional flow control valves

[Rajab84]

Dear All

I'm working on multiphase flow project, what I need to do at each set of experiment is to control the air flow and the liquid flow manually. The problem with manual system you can't get exact flow rate if you want to repeat the experiments. Therefore I should be grateful if anyone explains to me how to control these valves through labview. ( I've  Cdaq 9178 with NI:9203 and Ni :9472)

Best Regards 

Rajab

[stephencox]

You need to explain exactly what you are controlling and how.  Do you just have motorized valves that you need to control with Labview?  Do you just feed on/off to a motor on the valves?  If so, you presumably just need to use a timer to switch the motors on and off.  Does the valve have a positon indicator that you can read with Labview?  If so, you can use a simple while loop to adjust each valve to an exact position.  Do you have a way of measuring flow that you will monitor continuously and adjust valves?  If so, you just need a loop with something like case structures that run the motors in either direction based on the flow readings.

[Rajab84]

Hi Stephencox

Thanks for your reply 

Actually I've not got the valves yet, however they won't be on and off valves. it should be able to open like 10% 20% , ....etc. so I can adjust the desired flow. Basically instead of increasing the flow manually I want to use the control valves.

I just want it to have an idea before ordering any valves. 

1.     If possible, what kind of valves to order?

2.     Is the opening position will be controlled by the signal generated, example at 1v,, closed, 2 v 10% open .... 5v fully open?? If yes how to control the amplitude of the generated signal?

3.     I've flow meter on both lines to measure the air and liquid flowrate, how to adjust the valve position with the flowmeter reading??

4.     Is there any examples in the Forms that I can start with??

Best Regards

Rajab

[Petru.T]

Hi Rajab,

Are you using the 9203 to acquire the signals of the flowmeters? Do you want to use the 9472 for controlling the valves?

1. What valves to order? You can read through the manual of the 9472 (http://www.ni.com/pdf/manuals/373509e.pdf) and figure out what it can do.
2. The 9472 is a digital output module. I am not sure if it can adjust its output value as you wish: 1V for 10% opening, 2V for 20% opening and so on. If that is how you want to control your valves, then an Analog Output (AO) module will suit you better. Changing the output voltage level of an AO module is very easy in LabVIEW and there are comprehensive examples of doing this in the LabVIEW example finder, under Hardware Input and Output > DAQmx.
3. You can implement feedback control loops in LabVIEW. Are you interested in PID control?
4. I am confident that you can find examples on the community, but maybe an even better place to start is the aforementioned LabVIEW example finder.

Hope this helps.

[stephencox]

I have never used valves that work the way you describe, so I can't offer firsthand experience. What I meant by on/off is that you just turn a motor on and off and switch the polarity to slowly open or close the valve. If your flow rate changes gradually, this would actually be much easier to program. You just read the flow, say every second, and if flow is too high, turn valve on in closing direction. If flow is too low, reverse polarity. If flow is just right, turn valve off.

[stephencox]

As to what kind of valve to order, you will have to buy for your application. I imagine whatever you buy will have different controller options, so you will just have to make sure you buy something that you can control (or be willing to buy different NI modules). As pointed out above, you need analog outputs if you want direct proportional control. If you do it how I suggested, you can use digital outputs.

[JÞB]

Eh Why not,

a current project uses a few EPVs to mix water of various hardness (measured in grains) into two "Blend tanks"  The Valves are linked there to the spec and operate with 4-20mA current.

the Resource module is attached as an example of how this control is achieved.  The Task contains 4 channels of AO from a NI 9265

[Rajab84]

Hi Jeff·Þ·Bohrer 

Thanks for your help. I can't find the attachment. could you please attach the example?

Regards

Rajab 

[RavensFan]

It is a VI snippet.  Just drag and drop the picture from your browser to your block diagram.  Though depending on security settings, you may need to drag and drop it from the browser to the desktop first (then give permission for that to occur), then drag the file from the desktop to the block diagram.

[Rajab84]

Hi Petru 

Thanks for you support, sorry couldn't reply any earlier.

I’m still contacting different supplier to get the best option, however I suppose to use the 9472 for controlling the valves, since I don’t have (AO unit). I think PID control is required.

Best Regards

Rajab