I've got a PXIe/PXI DAQ containing one PXI-6624 counter/timer card. The card measures six different incoming frequencies. Everything works fine, until the frequency on two of the inputs (hardware redundancy) reaches about 6 kHz, when it appears that Ethernet communication between my DAQ and computer breakdown. I've gone through my wiring, but can essentially remove everything and reproduce this with a function generator wired directly into my SCB100a terminal box.
Eventually, I noticed in our software setup that the two spares on the pxi-6624 card were set up with the same PFI values as the two that fail at 6kHz. I changed those to the SOURCE values dictated in the SCB100a user guide (all the others use their associated SOURCE values,) but the DAQ becomes unhappy, telling me those values are already in use. I ended up changing the two spares to their GATE PFI values, and that let's me get up to 8 or 9 KHz before occasional, one second drop outs occur. Much better, but I still feel I'm doing something wrong, as this card can supposedly do up to 400 kHz.
I'm not specifying PFI usage anywhere else in my hardware setup and can't quite tell what's interfering with the pxi-6624. Any suggestions as to how to go about this?