Setting Voltage Range on PXI-6025E

[Ray00]

I am using a PXI-6025E card channels AI0 and AI8 differentially. Since the card is 12-bit I only get around a 4.88mV resolution from -10 to +10V. How do I change it, so that I am getting unipolar (0 to 10 volts) and my resolution is 2.44mV. MAX doesn't really seem to give me the option to change it (for testing purposes) and I really can't seem to do it programatically. I've tried a lot of NI examples, but none seem to do it, unless I am missing something. Some VI's say enter a low and high limit, but that doesn't seem to actally change my 4.88mV resolution.

I am trying to fix a problem where my voltage seems to jump around in increments of ~4.88mV, but my volt meter stays very constant. I did try averaging over 1000samples as
well. I need as much resolution and consistency as I can get. Any suggestions would be greatly appreciated.

[Ben]

Did you try setting up a virtual channel in Max. It is in that dialog/config screen that you are asked what the range of your signal is.

This is then used to configure the range that best fits your req's.

Ben

[Ray00]

Thanks, setting up a virtual channel helped. It turns out that the unipolar/bipolar setting cannot be altered on the 6025E (always bipolar), but I guess the gain is automatically adjusted when high and low limits are set. This is the feedback I got from an NI rep. My voltage still jumps around when I get down to 4 digits passed the decimal, but I think this might be do to the quantization error. I will be moving on to a 16-bit card eventually, so hopefully this takes care of that problem.

Thanks,
Rey

[Ben]

Thanks for the update.

I think you are right re:quantization.

Remeber, the data retuned from NI-DAQ is SGL. You will hit the SGL limit before you will find the limit of the 16 bit card.

Ben