Prob with AI on PXIe 6358

[LV_Enthu]

hello,

         I am using pxie-6358 for my DAQ purposes. i have a LVDT signal conditioner AD598 (+/-5V output) hooked up to one of the AI channels in the PXIe6358. i know that 6358 can support only differential inputs, and that's how i have hooked the output of LVDT signal conditioner. 

the weird behaviour is as follows:

1.  i move the LVDT core from zero position to positive max position, and I see the output in MAX(measurement and automation) going from 0V to +5V,
2. however, when I move the core from zero position to negative max position, the output in MAX goes only from 0V to -2.24V and then the output saturates to -2.24V...

  I connected a voltmeter in parallel with the AI channels on SCB 68 (that's how the connection is made to PXIe6358), i see correct output on voltmeter (0 to -5V). i also used another DAQ CARD USB-6009 to veriy if there is a problem with signal conditoner, however, things work CORRECTLY on USB-6009, i.e. when the core displaces from zero to +ve max, the output goes from 0 to +5V and when the core moves from zero position to -ve max, the output varies from 0 to -5V.

Can anyone suggest what posibbly be a problem? is this an impedance matching issue? i also tried different channels on 6358 just to make sure that particular AI is damaged, but the results are same...

[ianidas300]

Hello LV_Enthu

Are you using proper grounding and pull down resistor configurations for these measurements? The following is a link for proper field wiring considerations:

https://www.ni.com/en/shop/data-acquisition/measurement-fundamentals/field-wiring-and-noise-consider...

[LV_Enthu]

yes, i am .. i tried 10k and 20k resistor values, and the observation was same... also, i have read the white paper you posted quite a bit of times, and followed all the things mentioned out there

[ianidas300]

Try a simple battery test checking the positive voltage and then reversing the differential inputs to show negative voltage which should be the same magnitude only negative. A simple 9 Volt battery will be fine.

[LV_Enthu]

already did taht... and the PXIe card reads those values correctly... 

[Chris-NI]

Hi LV_Enthu,

This sounds a lot like a grounding issue.  Can you provide a connection diagram of your setup so we can see how everything is wired up?

Regards,