Using 6704 current output to control pressure regulator failure

[nithyan2]

Hello,

We are trying to use a PCI-6704 card to output 4-20 mA to a pressure regulator. The regulator also needs a 24 VDC supply and changing current signals through the same wires (2 wires: +,-).

Our connection is as follows:
Regulator (+) to +24VDC power supply
Regulator (-) to PCI-6704 (ICH17 - pin 32)
Power Supply (-) to PCI-6704 (ACH17 GND - pin 33)

However, there is no voltage supply to the regulator and changing the current output (using NI-MAX test panels) does not have any effect on the regulator, although there is a current output from the card.

We have tried connecting the Power supply (-) to AGND (pin 19) but that didn't work either. We also tried connecting the Regulator (-) and the power supply (-) together to ICH17 but that was no good.

So we are trying to find out how to do the wiring appropriately to suit our application. Any help/suggestions are welcome.

Thanks.

[lisan2012]

Hi nithyan2

Do you have a datasheet for the pressure regulator that you might be able to share with us as well? My understanding of you circuit would be a current source, load and voltage source, all connected in series, if this is the setup that you have I am not sure on which source would be the boss on your circuit.

Thank you!

lisan2012

[nithyan2]

Hi lisan2012,

I have attached the manual for the regulator (known as a beta positioner). Please see page 2 for the schematic. There are only two wires. I have confirmed this with a representative from the company, but they were unable to help with the wiring.

We have had this air supply system for a few years, and previously (before I came here) it was using a PC-AO-2DC card for the current output, and the connections were as follows:

Regulator (+) to +24VDC power supply
Regulator (-) to PC-AO-2DC (ICH0 - pin 1)
Power Supply (-) to PC-AO-2DC (AGND - pin 11)

(We are using an 'International Power' power supply which provides 24 VDC at 1.2 Amps.)

As I mentioned in my first problem statement, I have tried a similar setup with the PCI-6704 but that did not work. 

Please let me know if you need anything else.

And thank you so much for your help.