AI noise on 6035E

[Begre]

Hello,

I am using the AI on a 6035E board.  I am just using one of the VI examples (non-buffered) provided from LabView to get the reading.  The channels are set up to use differenial reading between Ch.1 and 9, and the range is between -0.5V to 0.5V.  I require reading down to 0.1mV.  I am getting a lot noise on my readings (the readings jump up and down even when I put a static load on it).  I have tried putting just a battery through it, short circuiting it, putting a VDC power supply on it and the noise is still there.  What is wrong?

Thanks

[Nicholas_B]

Hi Begre,

Have you tried these tests on other AI input lines?  Give that a try, but also use Test Panels in MAX first.  Make sure you choose the appropriate channel to read from and set up the measurement for differential readings.   Have you used this board in the past (without any noise issues) or is it a new device?

Also, here is a link to our Field Wiring and Noise Considerations for Analog Signals.  Please read over this document and make sure you have the appropriate connections.

Regards,

Nicholas B, National Instruments

[Begre]

Thanks for the reply.
I have tired the tests on the other AIs and it is the same thing (using both MAX and my VI).  This is not a new card, but I do not know if this had been a problem before or not.

[Nicholas_B]

Hi Begre,

Let's try this:  hook up a battery between AI0 (pin 68) and AI8 (pin 34)...make sure the positive terminal is tied to AI0 and the negative terminal to AI8.  Also, and this may be where the noise is coming from, tie a resistor (at least 10kohm) between AI8 and AI GND (pin 67). Whenever you are performing floating differential measurements, you want to tie the negative terminal to AI GND through a decently large resistor.  After hooking up the signals, open a Test Panel for your device in MAX and set the parameters appropriately:  Channel to DevX/ai0; Mode to Continuous; Input Configuration to Differential; and the default values for Max/Min Input Limits and Rate/Samples to Read should be fine.  After clicking Start, take a screenshot of the Test Panels window and post it back so we can take a look. 

Before you do so, use a multimeter to test the voltage on the battery so that we know what readings to expect.  Also please perform the same test on AI1 and AI9 (tying AI9 to AI GND through the resistor again) and post the screenshot. 

Regards,

Nicholas B, National Instruments

[Begre]

I tried the AI1 port the way you described.  Thanks.

[Nicholas_B]

Hi Begre,

Did you hook up the resistor between AI- and AI GND?  What value did you use?  What voltage are you expecting to read from the battery (did you monitor it with a multimeter?)

Also this Test Panel interface looks like you are using Traditional NI-DAQ.  Is that true? If so, which version of Traditional NI-DAQ do you have, and which version of MAX do you have?  I would suggest using NI-DAQmx to perform your data acquisition. 

One thing to note however, is that even though this voltage does jump a little, it is fairly constant.  You are only reading a 3mV swing between your high and low readings.  Depending on what you are reading from, this could be normal. 

Regards,

Nicholas B, National Instruments