Voltage readings from Ni cRIO-9215 are fluctuating a lot

[Fingal]

Hello!

I am trying to do voltage measurements with a Ni cRIO-9215 card in a usb-9161 carrier.

Problem is that my voltage input readings are fluctuating between 0.1-1 V even though my input signal is perfect. (No noise just a constant test input signal.)

 I have tried with different sampling rates but nothing seems to work. My labview vi is one taken from the examples of ai acquisition from daq-mx base 2.2 driver package. If I try with a different card (ni-4451) the readings are perfect. Behaviour is that when starting acquisition the readings are fairly good then after 10-20 seconds the readings tend to drop to values 0.5-1 V below what is the actual signal voltage. ( I test the signal input with oscilloscope at same time as data acquisition is run). From the start and during the whole acqusition, the voltage is fluctuating between 0.1 V very rapidly.

I run the vi in Labview 8.2.1 in windows xp and cpu workload is low during the measurement.

Any ideas?

Regards David

[Fingal]

Ok, looks like a hardware failure. The signal gets disturbed when I touch the acquisition box and the parts that should have zero tension fluctuates between 1-2 V. If I press on the box it gets even worse.

[laurentp]

Hello Fingal,

It looks like you should contact us (National Instruments) per telephone to arrange a repair process if wanted. NI Reception: 056 200 51 51

Best Regards,

Laurent 

NI Switzerland