Outputting Analog Current

[hreising10]

I would like to be able to control a device with a 4-20 mA signal in the most economical way.  We are already using aPXI chassis but we do not have a way of creating analog output.  Right now I am seeing the USB 6008 as the best option because we do not need that fast of a sample rate.  Are there any other options that I am not seeing?

[LV_Pro]

You will also need 249 ohm precision resistors as the DAQ has voltage inputs/outputs, which will have to be "converted" to current values.

[hreising10]

The positioner on the valve assembly has an equivalent impedance of 550 ohms already and the USB 6008 only outputs a 0-5 V signal though

[LV_Pro]

If you are trying to actually control a positioner then you will probably need more than just a DAQ card. 4-20 mA is usually a communications "protocol", rather than an actual "driver".

[AnalogKid2DigitalMan]

There are off-the-shelf converters for 0-5V in to 4-20mA out, they are typically bandwitdth limited to 100's or 1000's of Hz.

Dataforth makes a wide variety of conditioners and isolators, there are a lot of other companies too.

-AK2DM