Variable Power Supplied to Coil

[Pitt123]

I was looking at a controller for a hydraulic valve the other day and noticed that the controller seemed to supply a mA output current (up to 800ma) to a solenoid which controlled a hydraulic valve. I found it strange that a mA output was being used directly to control a coil for a valve. The voltage rating of the controller was 24VDC.

The coil on the valve was a DC coil. I guessing that the ouput current supplied a varying current to the coil and therefore a varying power to the coil to make the valve move between different positions. Has anyone ever seen this control direcltly on a valve or coil before? Can you explain relationship between current output, voltage ouput, power across coil and resulting coil movement? I'm assuming that coil impedance is fixed.

 

[Jraef]

It's called a "Proportional Control Valve", if you Google that term you will get lots of information.

 

[eric7379]

I know that Bosch/Rexroth makes them.

Here is a PDF file from the Bosch website on proportional control valves.

http://www.boschrexroth.com/country...en/industries_sm/a_downloads/ra09879_0503.pdf

A company that I worked for in the past used these on one of the machines that they made. It was a great concept and idea, but it was a PITA. What they were doing with them required a lot of control logic, which resulted in a lot of variables, which resulted in a lot of problems.

 

[Jraef]

I know that Bosch/Rexroth makes them.

Here is a PDF file from the Bosch website on proportional control valves.

http://www.boschrexroth.com/country...en/industries_sm/a_downloads/ra09879_0503.pdf

A company that I worked for in the past used these on one of the machines that they made. It was a great concept and idea, but it was a PITA. What they were doing with them required a lot of control logic, which resulted in a lot of variables, which resulted in a lot of problems.

Maybe some time ago, but they are just controlled by anything with PID loop control, the same way you would control any other analog control response device like a VFD or heating controller. Most of the people who make the valves now sell controllers along with them, but you can also hook them up to PLC analog outputs, motion controllers, DCS systems etc.

 

[Pitt123]

I read up on this a little. It appears that the controller sends a variable mA signal to the coil to move it different distances. I suppose the coil is moved according to the power applied to it determined by I^2*R outputed from the controller?

With the coil being a fixed resistance will the voltage output from the controller also change as the mA signal is varied? I assume it will.