Analog input problems using PXI 6232

[vadimuschka]

I've been trying to solve this problem for a while now without any luck. Any solution suggestions are welcome.

I am using a PXI 6232 with LabView 8.5.1 to input several analog signals from my sensors. Based on the signals a PWM signal is generated and output using PXI 6713.

Some of the analog input signals have spikes in them, that continuously occur during the runs. I looked at the same signals on an oscilloscope - no spikes. I change the setup of my hardware and the spikes still occur at the same spots. It seems like the program performs resets causing measurement errors. 

I attached the VI and a JPEG of two measured inputs.

Thanks in advance

Regards

Vadim

[Henrik_Volkers · Accepted solution]

I first was confused by your timescale 😉 but it seems that these spices occur every 20ms (not s) which point to a 50Hz line noise due to switched power converters (or an uncompensated diode bridges 😮  )

Another hint was your scope measurement. While using the scope you opened a groundloop so the spikes due to dI/dt through the groundloop found another way around. 

So I'm pretty sure that it is not the DAQ (in this case) it's your setup. 

Provide a clean (low R AND low L)  power path (keep them close and twist them slightly if possible) , add some filter to get down the dI/dt , identify the ground loops .  (Use your scope with a little coil as a sensor at the input and catch some magnetic fields can open eyes) 

THEN to clean the last spikes (out of the DAQ) to get the last ppm use chokes 

Message Edited by Henrik Volkers on 04-08-2010 09:20 AM

[vadimuschka]

Thanks Henrik,

I really hoped it was the DAQ, cause I've been hunting the ground loops for a while now - without any luck. Got myself different sensors/transducers, which changed the system' grounding connection slightly - no spikes (at leas nothing significant.)

Thanks again.

Regards

Vadim