What are acceptable measurement fluctuations for the SCXI-1126?

[kelvinator]

Greetings,

We are using an scxi-1126 module in a PXI-1011 chassis. The range for channel 0 is set at 2 kHz. The channel is configured for a threshold voltage of 0.1 with a hysterisis of 0.05. We are injecting a 1 kHz sinewave, 800 mV pp signal into the channel. The SCXI-1126 reading is fluctuating by as much as 0.6 Hz at all frequencies (below 2k). We have tried changing the window, signal levels and various other suggestions from the NI website with no success. Should the reading be more stable or are the fluctuations the result of the F-V conversion process? Any suggestions would be much appreciated.

[Sean_C.]

Hello,

Please look at the Specifications section of the SCXI-1126 User Manual (pg. A-3) at the following link:
http://www.ni.com/pdf/manuals/321844c.pdf

From the Accuracy Table for a 2 kHz range, the accuracy a year after purchase should be 0.0418% ± 0.308 Hz. Which for a 1000 Hz signal would be 1000 * 0.000418 + 0.308 Hz = 0.726 Hz in the worst case. 0.6 Hz would fall within the spec'd range.

Let me know if you have any further questions.

Sincerely,
Sean C.