How can I output bipolar currents (+/-10mA) with cRIO?

[Southern_Cross]

Is there any way to generate a bipolar +/-10 mA command signal with cRIO?

[LVbum42]

What kind of motor are you trying to drive?  

[Southern_Cross]

I'm driving a hydraulic servo valve from MOOG: http://unicorn-race.googlecode.com/git/doc/MOOG_katalog_samlet.pdf

[Southern_Cross]

Sorry. The MOOG servo valve I'm considering can be driven with the 9505 for power. But, another servo valve that I'm considering expects a bipolar +/- 10 mA command signal. There doesn't seem to be any way to generate a controlled low power bipolar current with a cRIO system... 

[LVbum42]

Hello,

Generally the 950x modules are used for motor control and you are correct that we do not have any analog output modules that drive the low power bipolar current on the cRIO.  However, we do have modules that output bipolar voltages which you could wire to a resistive load to generate the current you need.  I would imagine you would need a tighter tolerance for the load also.

[Southern_Cross]

Thanks. The 950x modules seem to be a sledge hammer solution for such a low power command signal. They are also PWM based signals which may or may not be acceptable when being used as a command signal as I have.

Using bipolar voltage through a resistive load is an option, I agree, but resistances don't remain constant during operation and therefore the current generation will vary. Since this is a command signal with side-effects using a non-regulated current command is unwise in my humble opinion... 

[AnalogKid2DigitalMan]

Use an off-the-shelf voltage to current converter, here is an example of one (there are numerous manufacturers):

http://www.dataforth.com/device.view.aspx?deviceid=331

You should also consider what bandwidth your require (this one is 1KHz).

-AK2DM

[Southern_Cross]

Agreed. I was just looking for a cRIO native solution to simplify cabling, mounting, clutter...

Another promising option is: http://www.viewpointusa.com/product/signal-conditioning/precision-voltage-to-current-converter/

[birch2413]

Were you able to get the system to work in this manner? I'm looking to use a Moog servovalve requiring a plus/minus 50mA signal. I'm currently considering the 9263 module for a bipolar 10v signal and then usign something like the 64-vcc to convert to bipolar 50mA. Anyone have experience setting up a system in a similar manner?

Thanks,

Ben

[Southern_Cross]

I know have a system up and running using the Viewpoint module (64-vcc) that I'm commanding from a cRIO 9264 module. It's working just fine.