USB-6002 analog input ADC noise

[LaserLisa]

Hello everyone,

I've run into an issue using the NI-USB-6002 with measuring an analog input. Under certain circumstances (which I will explain later) the signal I am receiving is showing some pulsed noise which is dependent on the sampling frequency of my DAQ.

This noise is NOT visible using an oscilloscope which lead me to the conclusion that it must be due to the hardware (limitations?).

When sampling with 20_000Hz:

with 10kS/s:

and with 1000kS/s:

As you can see the frequency of this pulsed noise is changing with the sampling rate. And now some words to my setup:

I am measuring the voltage of an potentiometer used in a linear actuator. The signal is connected to the analog input 0 and I already tried to measure with differential mode and RSE mode. The potentiometer is powered with 5V coming from the motor Controller and the noise starts to appear as soon as I enable the motor power output. When the motor is controlled with a external power supply the issue is not visible.

I know that it seems like a problem of the used motor controller but since the noise is not visible with an oscilloscope and the frequency of the pulses are changing with the sample rate I assume the cause lies somehow within the analog input.

Does anyone have an idea how to solve this problem? I was thinking to use a voltage follower to "decouple" the signal (I have not tried it till now because I don't have Opamp close by).

I will be thankful for any ideas!