"inaccuracy" of PXI-1052

[endeavor]

hello,

i'm using the system that consists of the following components:

1. PXI/SCXI combined chassis PXI-1052

2. seven different purpose SCXI modules (SCXI-1121, SCXI-1125, SCXI-1126 etc.)

3. PXI-6221 DAQ board

the problem is that any constant signal connected to any SCXI input (like resistor or battery voltage directly connected to SCXI terminal block) gives inaccuracy about 0,5% and dispersion about 0,5% (when acquiring with 100 S/s frequency). every time the quality of the input signal was checked with the oscilloscope. when using SCXI portion of chassis with only one SCXI module mounted we got the same results. changing SCXI modules to other, correct for sure, didn't help anyway.

when disconnecting SCXI subsystem from DAQ board programmaticaly, switching off its power and using DAQ board separately, we got normal voltage measurements without such incredible inaccuracy and dispersion.

so i suppose that DAQ board is working properly — it seems like peripheral bus of the combined chassis adds some noise to the signal.

does anybody know where could be the problem? thanks in advance!

[Efrain_G]

Dear endvr,

There are a couple things that I would watch for in your application. First of all, if your measurements are inaccurate, I would see when was the last time that your SCXI modules were calibrated. National Instruments recommends to calibrate your devices on a yearly basis to ensure that your readings are reliable.

As far as the dispersion problem, this might be related to your filter settings on your SCXI modules. For instance, the SCXI 1121 has a jumper selectable bandwidth. (Please see SCXI 1121 User manual)

[endeavor]

dear Efrain G,

thank you for your answer!

our SCXI modules are new and were calibrated this year. filter is set on 4 Hz (by jumpers and also by MAX).

[Efrain_G]

What is the voltage range that you are using? Your accuracy will decrease for larger voltage ranges.

[endeavor · Accepted solution]

Efrain G., 

thank you for your answer!

we've already settled our problem, there are no questions to NI.