Cannot get accurate voltage reading on SCB-68 with pci-6023e

[thor0411]

I am trying to measure the voltage output from a omega FMA-78P4 mass flow controller. It outputs signals from 0-5V DC corresponing to the flow rate. I have tried to get my PCI-6023e board with a SCB-68 accessory to read the voltage input in differential mode. I currently have the signal going into ACH0 and the common into ACH8. When I run the test panel for the NI-DAQmx, i get a reading of 10 that does not vary when I change the flow rate. I can see the voltage change by a multimeter, so the problem is somewhere in the interface to the SCB-68. What do I need to do to fix this problem? 

[Aaron O]

thor0411,

To make the voltage measurement, you should connect:

The Positive end to AI 0, PIN 68

The Negative end to AO GND, PIN 67.

This should provide a correct measurement for AI 0.

Regards,

Aaron

[thor0411]

When I connect in that fashion, I get a voltage reading of -1.2 V in differential mode and -3 V in RSE mode. When nothing is connected I get a reading of -0.07V.

[Curt_C]

Have you tried connecting + to 68 and - to 34 and 67?

Curt

[thor0411]

I just tried that. My voltmeter registers +3 mV coming out of the mass flow controller. I get a reading from the test panel of -0.01 V for differential mode and -0.08 V for RSE mode. 

[Curt_C]

Have you tried measuring another device?  For example, the output of a power supply or a battery to check the 6023e.

Have you tried another channel on the 6023e?

[johnfr]

Ch-0 of the SCB-68 has a jumper setting that can enable an on board Temp Sensor. Check the settings of S1, S2 S3, S4 and S5. Mine has the various settings on a lable inside the top cover. I think you will want to use the 68 Generic Terminals setting shown at bottom left of lable.