ni 9207 input +/-20/20 mA loop

[Gearmiester]

I am using a Pepperl+Fuchs strain gauge signal converter to supply a +/- 20 mA signal to an NI 9207. However, that is not one of the diagrams included in the manual (meaning I am not supplying loop power from the module) So if I were to connect the 0mA line to common and the Pos mA signal to AI8 will it read the signal being supplied?

The reason for using the NI 9207 instead of a strain gauge module is the distance between the field device and the cRIO. (@ 200 ft) The PnF converter is local to the strain gauge (3 ft) and sends the loop mA signal back to the cRIO.

thanks,

[SeaSick]

Hi GearMiester,

You should be able to connect the signal converter to the NI 9207 using COM and AI8.

I would take a look at the NI 9207 Manual specifically at page 12 where is discusses connecting current channels. It suggests that you install a 2A maximum, fast acting fuse between the power supply and the pins. 

http://www.ni.com/pdf/manuals/375206a.pdf

Regards

[Gearmiester]

SeaSick~

Thanks for the reply. I understand that I need an external power source if I am sending loop power to a sensor or thermocoupling as i an supplying power from the 9207 but in this instance the loop power is being generated from the signal conditioner. Hence the question. I will give it a shot with the com and AI8 and see if it actually reads the signal. The other thing I have to be concious about is that I will be supplying loop power to sensors from the same module (so they will have power though a two amp fast acting CB) but each channel should be isolated enough to be ok to allow one that does not follow the wire diagram exactly as supplied  in the manual. But if all the com ports are connected internally should I have a diode in the AI8 - com loop on the com input to prevent some kind of wierd backfeed?

[SeaSick]

Gearmiester,

I'm not very familiar with the Pepperl+Fuchs Strain Gauge Converter and how it outputs current, but as long as its the 0 mA line connected to the COM port you shouldn't need a diode on the COM input. I would be concerned that putting the diode there may skew the measurements. 

The White Paper linked below may be a good reference for measuring current with DAQ Devices.

http://www.ni.com/white-paper/7114/en/

Hope this helps!