Verifying 6052 and the 1520 Mux System

[HamptonVa]

Hi,

I have setup and scanned 8 channels with a PXI 6052e and a SCXI1520 with DAQmx using LabVIEW 7.

I then grounded Ch 0,2,3,4,5,6,7 in the terminal block and applied a 0 mVDC signal to Ch 1.  All my channels have a small amount of 60Hz noise, but it is so small I am not concerned.  As a note Ch 1 has the most noise which makes sense since the calibrator I am using isn’t the best, but even the noise of this channel is acceptable with gains of 1000.  My configuration uses 100 Hz filters and 4 KHz sample rates for each channel.

Previous threads have mentioned the DAQmx will optimize the gains for both cards based on the input range I select. 

Everything seems to work good except when I select ranges below 5mV, which would give me a gain of >1000. I have tryed moving my calibrator to differnet channels injecting varying mV inputs with no problems to report.  At no time did any of my channels over-scale.

As I selected ranges of 5mV, 1mV, 0.1mV and 0.05mV I expected my time and freq. domain plotted data’s noise to increase, which it didn't.  I really expected a difference in the noise floor between a gain of 1000 and 100,000 but couldn’t tell a difference.  Later using the DAQmx I have queried the settings of both the 6052 and the 1520 configuration.  The 6052 always shows an input range of +/- 10V while the 1520 will step down to +/- 0.010mV depending on the range I choose.

Is my 6052 card malfunctioning or did I miss a step?

Is there an easy way for me to prove the hardware is actually setting the gains correctly?

[stilly32]

Hi,

Setting the Max and Min values for the channel will automatically choose the gain settings for you. You can check the SCXI gain and DAQ card gain settings using DAQmx properties. The AI Gain property gives the gain of the SCXI module (max of 1000) and the AI Range High and Low values will give you the range of the DAQ card. The driver will max out the value of the SCXI gain setting and then alter the DAQ card's settings. Something like this is great for troubleshooting:

You can also use those properties to explicitly set those values if needed. You may just be running into the noise floor of the system - no matter how much gain you apply your noise floor will constant.   

Hope this helps,

Andrew S

Message Edited by stilly32 on 07-16-2007 04:29 PM