cRIO module for +-20mA ouput

[Richard_Ha]

I've got a requirment to drive a hydraulic servo valve from a CompactRIO.

The valve require +-7.5mA to operate.

I've only been able to find 0-20mA output modules for cRIO or PXI.

Does a +-20mA ouput method exist?

Many Thanks, Richard.

[MHutch]

Hi Richard, 

As I understand it, the sign on a current is purely based on the direction of current flow. This means that negative current is purely current flow in the direction that is not considered positive, from a lower potential to a higher potential. The logical conclusion to draw from the spec of the valve you specified is that any of the modules you've looked at would be fine, because really all you're going to be taking into account is the amplitude of the current, and not the direction. 

I hope this helps! 

Kind regards,

[Richard_Ha]

Hi

The servo valves are directional.

0mA - valve is nulled, no flow

7.5mA - valve is fully open in one direction (actuator opens)

-7.5mA - valve is fully open in the other direction (actuator closes)

Hope this clears it up a bit.

[MHutch]

Hi Richard,

Modules such as the 9264 that can generate a "negative" voltage will also have a corresponding "negative" current. But again this is just sign convention due to direction of current flow.

Kind regards,

[MHutch]

Hi Richard,

Could you provide me with any information about the valve? point me to some specificiations maybe? It would help me greatly to be able to see this and get a better idea of how to advise you on this.

Kind regards,

[MHutch]

The above being said, I assume you will be needing a device that can change the direction of current flow internally whilst in use. It should be noted that there is no hardware that offers such functionality for use with the cRIO. You would probably need something with better specs like an SMU. I hope this helps!

Kind regards,