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DAQmx Samples to Read Slowing Spreadsheet Write?

I know I don't understand something here but I'm trying to figure out what piece I'm missing. Im writing a producer/consumer loop to log thermocouple measurements from an NI9210/compact DAQ. I want to read data as fast as it's available from the hardware (2 samples/sec IIRC) and write it to a spreadsheet. 

 

My VI is as pictured, but whenever I set the "Samples to Read" on the DAQmx read to -1 (read whatever is in the buffer, not a specific number, correct?) and I run the VI for 10-15 seconds I only get 1 sample logged. If I set "Samples to Read" to 1 or 2, then I get approximately 15 data points, which is what I would expect for how long I run it. 

 

Obviously setting to 1 or 2 works, but I don't understand what's wrong with setting it to -1, as that is the default that should do what I want, right? 

 

 

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I would advise against using the Write To Delimited File.  It is constantly opening and closing the file.  Instead, use the File I/O API to create the file before the loop, write your header (still before the loop), write the data inside of the loop, and close the file after the loop.

 

I am also suspicious because your file header is showing 2 channels, but you are only reading 1 channel (1Chan NSamp).  How many channels should you be reading from?

 

Finally, with the rate you are reading data (500ms per sample is extremely slow to a computer), I would not use a Producer/Consumer here.  It can all be in 1 loop.  This will make things a lot simpler for you.  I would also just read 1 sample at a time using the NChan 1Samp (assuming you have multiple channels) option for the DAQmx Read.


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