DAQmx read feedback

[Tiff]

My goal is to set up a feedback system  within which analogue data is collected from a photodiode using a PCI - 6251 board, some calcuations are done in LabVIEW 7.1 and a signal is sent to an Intraaction frequency generator PCI board which sends an RF frequency to an acousto-optic deflector (AOD).

I have found that even with the simplest of programs (keeping the RF frequency ouput constant) I get a blip in the measured intensity each time the DAQmx read starts to read data.  I believe this is the reason because if the DAQmx is asked to read a number of samples per channel the blips are separated by this number.  Writing to file is done outside of the loop so should not interfere and the task is set up and closed outside of the loop so should also not interfere.  The blip is also observed  when data acquisition and frequency control for the AOD are run in separate programs.  It seems that DAQmx is doing something that is upsetting the frequency generator board.   I really need a known frequency to be sent to the AOD at all times for my experiments.

I would very much welcome any ideas on how I might overcome this problem

Tiff

[Stuart_R]

Hi Tiff,

Do you see the same behaviour when running one of the example programs?

Could you post some code that shows this problem?

Also, can you explain some more about what you mean by blip? Feel free to send any screenshots of charts etc that show this.

Thanks,

Stuart