Why cant Compact Fieldpoint read more than one voltage?

[stu22]

Hi, im using cfp 2120 with 3 cfp-aio-610. For some reason it is unable to read more than one voltage from my circuit at 2 separate points(see diagram). If i try and attach more than one analog input, I get high current plus Little voltage. Ive had help from NI but they have not been able to solve my problem. Beginning to think i should have stayed with my Agilent datalogger as this Works Fine.

Stu

[Wayne.C · Accepted solution]

stu22,

The user manual for the AIO-610 indicates that pins 18 & 20 (Common) on the AIO-610 are tied together internally in the module.  Looking at your circuit diagram, that would effectively short out the 'Load' and dump a large amount of current through your shunt.  Post some more info about your overall app and perhaps we can come up with a solution.

[stu22]

Thanks Wayne.C, that makes complete sense 🙂 I'm using the shunt to measure current(via voltage drop) and Voltage applied at the anode and cathode(load-electrolysis).  These are the two readings i require, using labview to data log.

[Wayne.C]

stu22,

The 4 input channels on a AIO-610 share a common ground reference that is isolated from other modules in the cFP backplane.  It may be possible to use the point between the shunt and load as the common reference to the circuit you are measuring.  You would be very limited as to what other signals could be connected to the module.