USB6356 daqmx read.vi takes too much memory

Question

I am using USB 6356 for data acquisition, when I took data, the DAQmx read.vi took more and more PC memory. Until certain point, show "there is no enough memory to complete".  I set 2Ms/channel and 1M Hz rate, I know it is very big. But it takes daat for 6-7 times without problem. My PC has 3 G memory.
It seems that DAQmx read store more and more data in buffer. I attach my vi here, please check it what mistake I did here or how to improve it.
Thanks Liming
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Attachments:
usb6356_memory_issue.vi ‏2797 KB

Answer 1

Hi detech,
Your VI uses a waveform chart. This type of display keeps a history of your previous waveforms, and each time you write to it new data is appended to the end of the history.
So in the first iteration of the loop, your graph is storing and displaying 2 million points-per-channel. In the next iteration, it tries to store and display 4 million points, then 6 million, and it will continue in this fashion until you run out of memory.
Aside from the memory usage, trying to parse a 2-million point or larger array and graph it is very processor intensive, and this will only get worse each iteration of the loop. I suspect your system is also getting slower and slower as you run the VI.
You can use a waveform graph in place of the waveform chart, which will not keep a history of your previous display, and resolve your memory issues.
However, it sounds like you need some amount of logging for your application. Can you describe what your trying to do with the data you acquire, and also post what version of DAQmx you have?
There are several ways built into the DAQmx API and LabVIEW to deal with large amounts of data, and I'm sure we can find one that will work well for you.
William Earle
National Instruments R & D | Staff Software Engineer | DAQ Software