Data Acquisition start(): NumScans argument ignored

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Joshua Walker
Joshua Walker on 27 Jan 2021
Answered: Srishti Sahni on 18 May 2022
I have a function that is called during my program that looks like the following:
function outputSingle(obj, magnitude)
stop(obj.dataAq);
flush(obj.dataAq);
preload(obj.dataAq, Write.getData(magnitude, obj));
start(obj.dataAq, "NumScans", 1);
end
start() in it gives the following message: "Warning: NumScans argument ignored."
The output is started earlier in another function with:
start(obj.dataAq, "RepeatOutput");
But as you can see in the first code section it is stopped and flushed.
I have confirmed that the output signal is being repeated when NumScans is ignored.
Can anyone answer why NumScans is being ignored, and how to fix this?

Answers (1)

Srishti Sahni
Srishti Sahni on 18 May 2022
I understand that the ignored argument, "NumScans" for the start() function is a cause of concern for you.
The function start(d,"NumScans",span) starts the background input acquisition to run for a finite span of time, specified as a number of scans. If the DataAcquisition has any output channels, the start occurs but the duration specification is ignored.
If you want to avoid this behaviour, please examine the output channels within DataAcquisition.
More details about the start() function and this behavior can be found on the following link: Start DataAcquisition background operation - MATLAB start (mathworks.com)

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