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DAQ Assistant and Write to Measurement File

*New to Labview*


The data obtained in "Write to Measurement File" and data displayed on waveform graph do not match.  In fact, the information in output excel file appears erroneous. 


Please help.




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Message 1 of 4

Please supply some data to support your statements?  You have given us a VI that requires DAQ hardware and signals we don't have.  You provided us an XLS file.  But we have no way of replicating the acquisition of your data.  Show us some differences between the front panel and your XLS file.

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Message 2 of 4

Thanks for the quick response.


My use case: I want to record data from a string potentiometer as well as load cell in order to create a pseudo tensile test machine.  


The issue previously described was caused by my write to measurement file set to "overwrite file" instead of append.  I was only recording the last sample set to the excel file.  By setting to append, I was able to get the entire dataset.


My new issue is that this data set is large as it is sampling every ms, however when I turn down the sample rate on the DAQ Assistant, I review an error as the sample rate is too slow for the hardware.  String Potentiometer is connected to NI9227 module and the Load Cell is connected to NI9237 module.


Is there a way to reduce the write to data file sample rate? It appears completely disconnected from the input sample size/rates to my DAQ assistant (no matter the setting I review roughly the sample data file size per unit time).  It seems that a shift register may be the right approach as the wait (ms) did not help and timed out the DAQ Assistant.





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Message 3 of 4

My recommendations.


1.  Get rid of the Express VI's and use regular DAQmx functions and functions to write to the file.

2.  Use a producer/consumer architecture where the producer collects the data, the consumer writes the data to the file.  The data is passed via a queue.

3.  If you don't want every millisecond's worth of data, in the consumer loop write only every X samples.  Or average together X samples and write that out.

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