MATLAB Answers

David P
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DAQ output randomly stops during continuous acquisition

Asked by David P
on 20 Jan 2016
Latest activity Commented on by Alex King on 3 Dec 2018
I am using the following code to output a constant voltage on channel 2 of a NI-PCI-6229 DAQmx device. I am using Matlab R2014a.
The problem is that after some period of time (sometimes 5-20 minutes), the device stops outputting the data continuously. After stopping, the device property: IsDone changes from 'flase' to 'true'. No error messages are generated upon completion.
devices = daq.getDevices;
s = daq.createSession('ni');
s.Rate = 10000;
s.IsContinuous = true;
addAnalogOutputChannel(s,'Dev1',2,'Voltage');
outputSignal = ones(s.Rate,1);
queueOutputData(s, outputSignal);
lh = addlistener(s, 'DataRequired', @(src,event) src.queueOutputData(outputSignal));
startBackground(s);

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2 Answers

Answer by Rebecca Krosnick on 22 Jan 2016

I tried running your code in MATLAB R2014a (after creating the simulated device in NI MAX) and got the following output in MATLAB:
Warning: This change caused queued output data to be flushed. Use queueOutputData to queue data before starting the object.
Queue at least 5000 scans to output buffer. See NotifyWhenScansQueuedBelow for more information.
Did you not receive these errors? Try changing "outputSignal" to be a vector of 5000, as the error message suggests. For example:
outputSignal = ones(5000, 1);

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Yes, I replaced this piece of code with 1 to make it simpler to understand my problem, but I didn't realize it was wrong. The output vector should be a vector of ones. I have changed this in my original question now. Thanks for your response and sorry for the confusion.

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Answer by Timothée
on 23 May 2018

Hi,
Did you solve this problem? I have the same issue. It stops after around 3.5 hours at 1MHz and this time seems reproducible.

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This was several years ago, and I don't recall finding a solution.
I'm also having this issue, with both the NI USB-4431 & USB-6356. I'm trying the suggestion from the other answer now, queuing more than 5000 samples of output data, even though I do not get this warning.
The time it stops seems to be reproducible here too (although different for the two cards). I will try to find time investigations with different sample rates. Perhaps it has to do with the buffer size of the card?
Windows 7 & 10, MATLAB R2018b

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