Compact daq multiple power supplies into analog input

I'm trying to read several values from different sensors into a 9205 voltage input module using a compact DAQ. My sensors use different power supplies, they all output voltage between 0-10Vdc. I can read the value off of any one sensor fine, but once I hook up another both values start to shift and osscillate, however either one by themselves gives me a steady DC value. I am taking differential measurements from the sensor's outputs... I'm not sure if it would be ok to tie the grounds of the two power supplies together and feed them to my ground reference input of the module, if I take a voltage measurement between the two power supply grounds I see about 1Volt difference.
Any ides/suggestions would be appreciated.
Thanks,
M.

Hi,
I have been looking at the sensors you are using and the pins seem to be correct so I just want to make sure that we are on the same page with the connections you are making. This is assuming you have a spring terminal on your daq card rather than a DSUB.
Humidity Sensor - Pin 3 or 4 (CHn+) to AI0 (Pin 1) and Pin 6 (SGND) to AI8 (19)
CO2 Sensor - V to AI1 (pin 2) and 0 to AI9 (Pin 20).
In your software you should then be taking a differential voltage reading on AI0 and AI1.
Assuming that is all correct then this is very strange. The wiring diagrams suggest that the signals are ground referenced so this should be sufficient however the 1V difference in the ground lines is perculiar if they are plugged into the similar place. although the differential reading will eliminate error due to this one consideration is that if they are floating you may need to add bias resistors. You can find out more about this here. As I said it doesn't appear that this should be required but is worth a go if you have the kit to try it.
Otherwise it might be useful if you can send me some screenshots of the behavior on the graphs and perhaps your code and we can see if that helps. Also if you are able to verify the functioning of your sensors some other way would also be useful i.e. with a multimeter.
Regards,
James Mc
========
CLA and cRIO Fanatic
wiresmithtech.com/blog

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[email protected] wrote:
>
> Need to sample from the serial port and 4 channels
> of analog input at the same time. Figured I need
> to use an internal clock to sync the aquisition
> since the serial port response delays every so
> often. Does anyone know how to sample from an I/O
> port and a DAQ card at a consistent sampling
> frequency in LV? Any help would be greatly
> appreciated.
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Compact daq multiple power supplies into analog input

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