DAQmx Read Performance

[Louis Manfredi]

Hi Folks:

I'm doing a little project with DAQmx read analog 1D Waveform, N channels, N Samples.

The system under test is a fairly slow process in a noisy environment, so I'm sampling the data at (for example) 600 Hz, and reading the data 300 points at the time, and block averaging those 300 points into a 1/2 second averaged frame.

Calling the DAQmx read twice a second seems fine, but if I try to call it four times a second, things begin to get behind and the buffer overruns. Still have the problem at a lower sample rate, say 300 Hz sampling, reading the mx buffer 150 frames twice a second works fine, reading 75 frames four times a second gets behind.

I could sample the data in larger chunks, and break them into block averages separately, but I'm also polling a digital scale through a serial port, and I wanted to keep the program simple by using the DAQmx read to pace the overall sampling loop, and thus keep the scale more or less synchronized with the a/d data.

I don't recall in the pre-mx days that there was this kind of overhead issue in the old pre-mx AI read functions. (Which I'd rather not use because I'm relying on the mx for signal scaling, gain setting, and all that other stuff it does so nicely.)

Any suggestions for things to try to make the DAQmx read faster?

Thanks, & Best Regards,

Louis