Inaccurate output from analog outputs of NI PXI-6221

[jimpag12]

I'm using an NI PXI-6221 to output 1.5v from the analog outputs. For the purposes of the test the voltage needs to be accurate.

According to the spec the voltage on the outputs should be withint 3 millivolts, yet when I put a scope on the ouput the signal varies from 1.48 to 1.52, mostly towards 1.52.

I'm getting failures in my test due to this voltage being high.

Does anyone know if this voltage level is expected?

The card is in a NI PXI-1044 14-Slot 3U Chassis with (1)NI PXI-8105 Core Duo 2.0 GHz Controller, (6) NI PXI-4110 Triple-Ouput DC Power Supply,0-+6V,0-+20V,0- -20V,1A, (1) NI PXI-2527 64-Channel 300V CAT I Multiplexer, (1) NI PXI-6514 Industrial 32 DI, 32 Source DO Isolated DIO & NI-DAQ, and (1)NI PXI-4071 7 1/2 Digit FlexDMM (1.8 MS/s Digitzer,1000V,1pA-3A)

Would noise from the other instruments cause this fluctuation?

[Hooovahh]

How are you measuring the signal?  Is it with twisted sheilded par wire?  What about the length of wire?  Or the resistance of the connection?  Electrically what is the environment like, is there alot of high voltage, high frequency noise, motors or antennas?  A little bit of Heisenberg maybe in order as well, by that I mean measuring the signal will affect its reading.

Where in the spec does it say 3 mV?  I see it is a 16 bit output, and range from +/-10V which would give each bit a value of 0.3mV.  I don't think you'll be able to measure 0.3mV in very many environments but your swing of +/-20mV does seem a little high.