online analysis on background data, ni card analog input

Question

Ehsan 2019-1-14

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/439762-online-analysis-on-background-data-ni-card-analog-input

编辑： Ehsan 2019-1-24

Hi,

I am trying to get access to a global variable that is updated in the listener function of a ''DataAvialable'' event, relating to the startbackground for NI card analog input.

It seems that neigther a global variable nor the "UserData" of the daq session object are not updated before stoping the background recording. Is there any way around this to get online access to a variable that is updated in the listener function while the recording is still running?

Thanks,

Ehsan

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Answer 1

Kenny Shu 2019-1-23

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https://ww2.mathworks.cn/matlabcentral/answers/439762-online-analysis-on-background-data-ni-card-analog-input#answer_357660

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When the session's "UserData" variable is updated in the "DataAvailable" event callback, the result is immediately accessible from the workspace.

By setting up the listener as follows,

s1 = daq.createSession('ni');
s1.addAnalogOutputChannel('Dev1','ao1', 'Voltage');
s2 = daq.createSession('ni');
ch = s2.addAnalogInputChannel('Dev1','ai1', 'Voltage');
ch.TerminalConfig = 'SingleEnded';
s2.DurationInSeconds = 60;
lh = addlistener(s2, 'DataAvailable', @dataAvailableCallback);
s1.queueOutputData(linspace(0,10,30000)');
startBackground(s1)
startBackground(s2)
function dataAvailableCallback(src, event) 
src.UserData = [src.UserData; event.Data];
end