USB-6251 Input channel displaying incorrect waveform

[jchsu]

Hey guys,

I'm using the USB-6251 to acquire data from an output that the device is generating.  The output is a chirp signal with starting and ending frequencies that the user can input and it has a fixed amplitude.  I am sampling this signal with 4 different input channels, all at the same rates.  All this is programmed in LabView.  Channels 1,3, and 4 all display the same signal that the output is sending out (which is what I want).  However, channel 2's signal becomes smaller as the frequency gets larger.  

For instance, if I had the starting and ending frequencies of my chirp signal as 2kHz and 80kHz respectively, the wave sampled in at channel 2 would have the expected amplitude at first, but as the frequncies get larger, the amplitude gets smaller.  The opposite happens if I start at 80kHz and end at 2kHz (starts small, ends with the correct amplitude).

So somehow, higher frequencies are being filtered out, but only on channel 2.  I made sure all my wires are ok as well.  Is there anyway to fix this or is my board just faulty at channel 2?

Thanks,

Jeremy 

[jschwartz]

Hi Jeremy,

I would try moving your channel 2 signal to channel 5, so you will be acquiring on channel 1, 3, 4, and 5.  If all your channels read correctly in this situation, I would suspect that your channel 2 is faulty.  If you believe that the board is broken, you can create a service request at ni.com/ask and be sure to set the Question Type to Returning hardware for repair/replacement/calibration.  You can then call 1-866-275-6964 with your service request number that you have created.