I have a cDAQ-9174 and need to acquire the power of a 3-phase system. The voltages are taken from the secondary of the VTs (100 Vac using NI-9225).
The problem is to acquire the current. The secondary of the CTs gives 1A nominal current (max). I am using a Fluke Clamp i5S that gives to me 400mV/A. Have tried using the NI-9215 (-10 to 10V), but due to the values are too small, the measurements are imprecise.
Also have available one module NI-9203 (-20 to 20mA).
Do you have any suggestion of connection or programming to improve these measures?
I've used the 9239 on a project for CT signals. Still +/- 10V but 24 bit helps a lot with the dynamic range. Thats on a ~1V/A clamp at 1A nominal.
Ultimately you need to work out the largest and smallest signals you need and at what precision. Both the NI cards you reference are 16 bit which limits their dynamic range (smallest - largest signal). Averaging can improve some accuracy but if your signals are below the noise floor of them I don't think much can be done (other than to boost the signal by using a clamp with a higher output).
James Mc ======== CLA and cRIO Fanatic My writings on LabVIEW Development are at devs.wiresmithtech.com