Interference of analog inputs

[nemotora]

Hi,

I have problem with analog input measurement. I am using NI PCIe-6351 for measuring voltage signal from 3 sensors - accelerometer (differential connection to AI4) and 2 pressure sensors (differential connection to AI0 and AI1). If I measure signal from accelerometer and pressure sensors separately using SignalExpress everything seems working. However if I measure these signals together it looks like they influence each other, concretely analog signal of accelerometer increases value of pressures during dynamical measurement. Measuring only pressures looks all right.
Behaviour of signals is shown in the figure below. Upper two figures show separate measurement of signals AI0 and AI4, bottom figure shows signals measured together/simultaneously (signals are noisy but they should be constant).

Thank you so much for your suggestions.

Jaroslav Bušek

[PackersFan]

This is a great resource for any problems with acquiring analog signals:  Field Wiring and Considerations for Analog Signals

[ValkoA]

Dear Jaroslav!

If I understand your image correctly, the issue is the oppositve of what you described, so the accelerometer (AI4) is being affected (offset by a fairly constant DC value) by the pressure measurement (AI0). What is your measuring frequency? 

There are a few suggestions off the top of my head:

1. Check shielding on your sensors to ensure on crosstalk is happening on the measurement itself.

2. Create a dummy task on AI3, measuring a constant 0 to zero out your ADC in between channels.

3. Depending on your application, you could decrease the sample rate on one, or all sensors. 

Hope some of this you'll find useful.

Best regards:

Andrew Valko

NI Hungary