Is the cRIO 9401 DIO backplane and the cRIO 9205 analog input module share a common?

[Scottyd]

Is the cRIO 9401 DIO, cRIO 9074 backplane and the cRIO 9205 analog input module share a common? 

I have LabVIEW realtime, cRIO 9074 chassis running a scan engine program, a 9401 TTL DIO module for my counter and a 9502 as my trigger monitor.

The counter does it's job just fine until the trigger initiates. the DIO count is affected on the up and dowm of the 5 Vdc signal from the trigger. the counter jumps from a random number for example 2.3 to 24.7 gallons. The counter had been counting up steady at a 1/10th gallon per 5 second pace then wham. The flow meter uses a 5 Vdc PNP pulse as its counter. at a 1/10th of a gallon per pulse. pulse width 250ms.

the ground plane is the only common thread. I am purchasing an isolating amplifier to isolate the flow meter pulse from the rest of the triggers and transducer grounds affecting my pulse measurement, it is intermittent but creating some gain from the counter., it jumps at the initial rise and also at the falling edge of the 5 VI trigger.

[Queen_Nadine]

Hello Scottyd,

No, the cRIO 9074, NI 9205, and NI 9401 do not share a same common.  Here are the Specifications sheets describing the Isolation Voltages specifications of those modules:

NI 9401 Specifications (p.18)

NI 9205 Specifications (p.27-28)

You can however tie their commons together.

I hope this helps!

[Scottyd]

Thank you for the quick response, I believe the common is tied to each module thru my connections, hence the jump on unrelated sensors. the only thing they have in common is.... well, the common ground. I will try to isolate the ground of these sensors and transducers to eliminate the interference.

[Queen_Nadine]

Hello Scottyd,

I would also highly recommend the following White Paper that discusses Field Wiring and Noise Considerations when dealing with Analog Input measurements. Table 1 is especially useful:

Field Wiring and Noise Considerations

Regards,

[Scottyd]

Thank you for the recommendation, I will check all the 9502 modules for the (pin 17) AI Ground connection. we are set up for differential measurement, but if the ground at AI ground isn't properly grounded to earth, we may be seeing these issues intermittently. Thanks again.