Using sample clock in DAQmx timing

[khng]

Hi: I have an application to generate an analog output using arbitrary pulse waveforms. I use the onboard sample clock to time the output. For whatever reason, I'm not getting the rate I set for the output. For example, if I set the sample clock to 100kHz with a pulse train interval of 10Hz, I only get about 30Hz in the output. Lowering the sample clock to 10kHz gives me about 8Hz in the output, etc. Since the pulse waveform is created at 100kHz, and if the DAQ is clocked at 100kHz, shouldn't I get the 10Hz pulse train I expect? Is it possible the timing is limited by the speed of my computer?

When I set the timing to use waveform source, it seems to work as expected but I've not tested it extensively.

[Sandra_T]

Hello khng,

From your post it appears like you are trying to writing samples at a rate of 100kHz to form a periodic waveform with interval frequency of 10Hz.

What hardware device are you using to do this? Can you give more information on how you are programming this task?

One reason why you might not be getting the expected pulse train interval is the signal isn't generated at the specified frequency that you are programming. The sampling rate is determined by an onboard counter. The limitation on counters is that they can only increment or decrement by interger values. The time base is divided down by the counter to create the sample clock. Consequently, valid sample rates will depend onyour time base and the resolution of the counter.

Regards,
  Sandra T.

Applications Engineer | National Instruments

[khng]

Sandra- I use a DAQCard 6715 with a BNC 2110 connector box. I generate the 10 Hz pulse using the "simulate arbitrary signal" function with a sample interval (dx) of 10 usec. I set the sample clock rate of the DAQmx timing to correspond to this sampling interval, i.e., 100 kHz. Are you saying the onboard counter is not able to divide down to 100 kHz?