Can I use a separate power supply to power an FP-DI-301 from that of the load being monitored?

[Pete Calleja-Gera]

I am intending to use some FP-DI-301 discrete input modules to monitor some loads. If the Fieldpoint system is being powered by a 24VDC battery source and the supply to the loads is from lab bench power supplies, will the FP-DI-301 read the input voltage correctly, as I believe the input is referenced to the FP-DI-301's COM supply (in this case the negative of the battery source)?

[Aaron_G]

Pete,

Every FieldPoint I/O module has an isolated I/O stage. This means that the common of the I/O module is isolated from the common of the backplane (which is the common of the network module). FieldPoint modules are rated for a working isolation voltage of 250 Vrms. This means that if you earth ground the network module (e.g. a common of 0 volts), you can connect the common of a FP-DI-301 to a value of 200 Volts, and be able to measure signals that range from 200 to 230 Volts with respect to the earth common. If you "cascade" wire the modules (e.g. wiring the V & C terminals of one module to the next) you bypass the isolation between those modules. If you cascade the network module, you totally bypass all isolation.

For further information, please loo
k at the following KnowledgeBase Article:
http://digital.ni.com/public.nsf/3efedde4322fef19862567740067f3cc/597c2b4cecef6bb586256831005b913f?OpenDocument

Regards,
Aaron