live operations on acquired data stream

3 visualizaciones (últimos 30 días)
LO
LO el 14 de Jul. de 2021
Comentada: dpb el 15 de Jul. de 2021
I am trying to plot and make online calculation on analog data acquired through a national instrument device. I am using the following code. With this code I am able to plot the acquired data live, on two different subplots while writing data on file.
I would like at the same time to perform operations while data acquisition goes on. something simple: are voltage level passing a certain threshold? what's the freq of the signal ? I added a line (now commented) in the logData function... in the example I am trying to calculate the mean of the acquired data chunk plotted in that moment. However if I run the script it gives me a lot of warnings (it calculates the mean though).
If I try to perform slightly more complex operations I get no outputs and a lot of warnings about errors... I guess it could simply be that acquisition is too fast to perform any of these operations... would it be possible to buffer the data somehow to allow this to happen? I am not even sure if that's the problem, perhaps it is a matter of adding more listeners/callbacks/functions ? I tried to test these ideas but I had no success... I would be glad to get any feedback ! Thanks
% create session
% daq.reset
d = daq.getDevices;
s = daq.createSession('ni');
s.Rate = 20000; % sample rate
Fs = s.Rate;
s.DurationInSeconds = 10;
% add channels
ch4=addAnalogInputChannel(s,'Dev1','ai0','Voltage');
ch4.TerminalConfig = 'Differential';
ch5=addAnalogInputChannel(s,'Dev1','ai1','Voltage');
ch5.TerminalConfig = 'Differential';
% add listeners
lh = s.addlistener('DataAvailable', @(src, event) logData(src, event, fid1));
% start recording
tic
s.IsContinuous = true;
s.startBackground;
pause(duration);
s.stop % end recording
toc
delete(lh);
function logData(src, evt, fid)
% Add the time stamp and the data values to data. Toda write data sequentially,
% transpose the matrix.
% Copyright 2011 The MathWorks, Inc.
data = [evt.TimeStamps, evt.Data]' ;
subplot(2,1,1)
plot(data(1,:),data(2,:));
xlabel('Time (s)'), ylabel('Amplitude (V)'), legend('ai0')
ylim([-0.5 0.5]);
subplot(2,1,2)
plot(data(1,:),data(3,:));
xlabel('Time (s)'), ylabel('Amplitude (V)'), legend('ai1')
ylim([-0.5 0.5]);
% mean(data(1,:))
fwrite(fid,data,'double');
end
  5 comentarios
LO
LO el 15 de Jul. de 2021
Tank you, this is actually useful. I wonder if there is a way to estimate the limit of "computing power" during an acquisition session. I will check the documentation. Thank you again.
Basically my aim is to perform online zerocrossing analysis to determine the instant frequency of a modulated signal. I will post the code here if I make it :)
dpb
dpb el 15 de Jul. de 2021
Certainly is no way to estimate a priori; you'll find out when you can't get everything done you're trying to before the next packet arrives. With MATLAB and all in m-files unless you can keep things highly vectorized and minimize screen refreshes, you won't get a tremendously high throughput -- it is still, after all, interpreted/compiled, not fully compiled to object code.

Iniciar sesión para comentar.

Respuestas (0)

Productos


Versión

R2018a

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by