Loss of samples in PCI6071E

[sergey 671]

Configuration: DAQ board PCI6071E, win2K, LabView 6.02.

I took a simplest "Acquire n samples" VI and set it to acqire data from one analog channel for 5 sec., 1000 samples/sec. The signal had two levels: 0 and 5 volt with a period of 100 ms and duty cycle 50%. I expected to get value toggle each 50 samples, but ~ each 1 sec there is a packet of 49 values and not 50. It seems like there is a problem with the DAQ clock - can it be calibrated ? How can I check (say, with a scope) what is the real scan rate of the DAQ - is there any scan strobe output I can check ? Any other ideas ?

Thank you,
Sergey.

[Filipe A.]

Hello;

That's strange. I can't think of anything that can cause that to happen. One test you can do is to apply an external scan clock of 1KHz, and double check the number of samples on each 1sec packet. If that is still 49, there is something else that you are overlooking on your setup. Otherwise, the internal Timebase might have some problems. You can also try to increase the sample rate to see if there is a consistent error.

Regards
Filipe A.
Applications Engineer
National Instruments

[Ben]

Filipe,

Could this be a requested sample rate vs actual sample rate issue?

Ben