Data Logging: Disk Vs Memory

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Ted 2011-9-21

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https://ww2.mathworks.cn/matlabcentral/answers/16314-data-logging-disk-vs-memory

I am having a hard time with different data logging modes during data acquisition. I am using an NI-DAQ PCI-6110E to acquire an analog input signal. I am triggering the acquisition repeatedly on an external digital TTL line connected to the PFI0 input of my DAQ card. I will post my code if there is interest.

The problem I am having is I want to acquire a large amount of data (1MS/sec for 4-6 sec) continuously. I am unable to acquire more than ~2 sec of data using the 'Memory' logging mode, I get a memory error. However, when I try to use the 'Disk' logging mode, my device misses almost 90% of the triggering events I ascribe to it (for example, if I ask the trigger to repeat 1000 times, the trigger will execute 9 or 10 times. If I repeat 2000 times, it executes about 17 or 18 times). The failure of the trigger to repeat occurs both when my TriggerType is Immediate and HWDigital signal. I do not get any run time errors in the Event Log. Any advice?

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Ted 2011-9-23

Yea, I was getting a similar estimate. I am not super-familiar with data storage types in MATLAB, but the EventLog is a structure array, with 4 data points for each logged event. If each data point is stored as a 64-bit double (I am guessing the structure array requires more memory than just 4 doubles, but that's a start), then including the data I am acquiring with the EventLog data, there are 6 data points recorded for each sample (is that right? 4 EventLog data points, an analog data point, and the sample number associated with it). so that would be 8*6=48 bytes per sample, so for 1M samples per second that's 48Mbytes/second. So 3 seconds would have me at 144Mbytes. Is that something MATLAB can store in its memory? I don't know if that's a lot or a little. I also don't know how to check how much memory each sample point is taking up.

Walter Roberson 2011-9-23

144 megabytes should not be a problem on any system with 3 Gb or more of RAM (as a rough estimate.) Though depending on exactly how it stores the data and exactly how it grows the buffer, it could temporarily need that much more. I definitely would not expect problems at ~100 megabytes unless your RAM is fairly limited and you do not have virtual swap space configured.

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