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valve modulation

Posted: Thu Mar 04, 2010 3:56 pm
by schroeder1214
Hey all, Old hvac controls guy here that is looking into automating some irrigation and general home control. My question is this; Is there an application that would allow me to control an analog water valve that takes a 4-20ma input?

Thanks.

Re: valve modulation

Posted: Thu Mar 04, 2010 5:29 pm
by fraser
do you have more specs or a datasheet on this valve? If so i could take a look for you.

Fraser

Re: valve modulation

Posted: Fri Mar 05, 2010 11:56 am
by schroeder1214
Thanks for the reply Fraser. But actually no I can't give you any specs on the valve because I haven't bought and/or built it yet. Phidgetsbc by far is the system that will work the best for my application except for this valve issue so I am trying to design it around the sbc. What is happening here is there will be 6 garden boxes "zones" that will be watered based on the comparative ratio of soil moisture setpoint and actual soil moisture. So to keep the system balanced as zones turn off and on I was going to have a min/max psi setpoint with a 3way mixing valve just past the pump to bypass or add pressure as needed based off a gauge sensor. I could always set the system up as more of a constant volume operation but I was hoping not to have to.

Thanks,
Matt

Re: valve modulation

Posted: Fri Mar 05, 2010 1:26 pm
by fraser
Well it is likely possible. It all depends how the valve works. Does the 4-20mA input control the position of the valve (i.e. 4mA = fully closed, 20mA = fully open) ?

Re: valve modulation

Posted: Fri Mar 05, 2010 2:19 pm
by schroeder1214
Yes. I was hoping to use a Belimo actuator that would accept either a 2-10vdc signal or 4-20ma signal. Here is a spec sheet on a typical actuator.

http://www.hekta.org/~hp04-72/HTML_side/Sluttrapport/Vedlegg/LM_Series.pdf

Re: valve modulation

Posted: Mon Mar 08, 2010 9:52 pm
by schroeder1214
Not sure if you are still watching this thread but this is the valve I would like to control. Thanks in advance for any help.

It's actually 0-10vdc modulating with spring return.

http://www.temcocontrols.com/product.php?ProductID=89&CategoryID=8&PHPSESSID=6ae20a30bf0f12ccc4ee2b3bb0d388d4

Re: valve modulation

Posted: Tue Mar 09, 2010 12:22 pm
by fraser
well unfortunately Phidgets doesn't sell anything that will let you control a 10V signal "right now," so you might have to find some alternate way of generating that control signal.

Re: valve modulation

Posted: Tue Mar 09, 2010 12:50 pm
by schroeder1214
Thanks Fraser.

Just so I am clear in this I don't have any options for controlling something that is 0-5vdc, 0-10vdc or 4-20ma? Not just 0-10vdc right?

Thanks again for your help and sorry if these are "noob" questions.

Re: valve modulation

Posted: Wed Mar 10, 2010 11:32 am
by fraser
Right now we do not have anything that will let you directly control 4-20mA or 0-10VDC or linearly control a 0-5V signal (we only have digital control). We have plans for such a product (-10VDC to 10VDC control) but there is no set date or scope of when it will be released.

So as it stands you wouldn't be able to use Phidgets to control that valve/actuator I'm sorry to inform you of that.

Re: valve modulation

Posted: Wed Mar 10, 2010 5:34 pm
by schroeder1214
That's alright. Everything else is going to work well with the Phidget. I'll come up with something for the valve.

Thanks again for the help.