inaccurate voltage reading using PCI6281

[zacharia01]

I am trying to acquired data from a fluke pressure transducer PV350 using PCI 6281. The transducer is battery powered and I am acquiring the data in RSE mode. But instead oif expected constant voltage, i am getting fluctuating readings which look noisy, Needless to say the MAX test panel results least resemble the actual voltage. This transducer gives correct voltage readings when I use a DMM.

What is going on wrong here. Please help...

Many thanks in advance,

Zach

[AnalogKid2DigitalMan]

If it's battery powered, maybe differential mode (DIFF) is a better way to go. There should be discussion of it and how to wire it within the manual for the 6281

[zacharia01]

Thank you very much for the suggestion about the DIFF mode. Between the 6281 and the transducer output, we have BNC2111, the connector module. They accept BNC from the transducer side and it looks just straight forward to plug that BNC into the one of 16 AI channels. Am I missing something, terribly here. I have gone through the technical manual, will re-read it again and try to extract what it says.


greetings,

Zach

[Jeff_T.]

Hi Zach,

Sometimes the autoscaling feature in MAX will zoom so far into a display that the readings appear much more eradic than they really are.  This is especially true in DC measurements.  What is the magnitude of the fluctuations that you are experiencing?  

Thanks,

Jeff Tipps
Applications Engineer
National Instruments

[zacharia01]

Hello Heff.

I believe it is not the problem with display in MAX. The voltage I am expected to see is around 1.1 V with a fluctuation of 0.1 V. However,
I see all voltages between -10 and 10, the default range of the AI. I believe this is some sort of connection problem. However, I have no idea how to go about.
 

[Jeff_T.]

Hello Zach,

If you are reading in RSE mode, make sure the two terminals coming off your battery are connected to AI0 and GND.  If you are reading in DIFF mode, make sure your two terminals are connected between AI0 and AI8.  When reading in Diff mode you only need to select "DevX/ai0" in MAX.  It already knows to use ai8 in conjunction with ai0 in differential mode.  Give that a shot and let us know how it goes.  Good luck!

Best Regards,

Jeff Tipps
Applications Engineer
National Instruments