Taking continuous analog data USB 6009, I am getting time lapses in the data?

[VPB]

I am using a USB 6009 to continuously take analog data with Signal Express. I am measuring three channels @ 2 samples/ 60HZ and saving the data to a text file. The problem I have is time lapses in the data recorded that go from .070 sec to 7 secs. I have turned off all of Windows automatic updating, Windows defender, and the screen saver. This machine also has had the virus scan removed.

[G_Lo]

VPB,

It does not seem like this is the case, but are you making multiple records?  Also, did you mean that you are taking 2 samples per channel at 60Hz sampling rate?  Could you also attach a screenshot of your code or the file that holds the data values. 

[VPB]

I am taking 2 samples @ 60 HZ using Signal Express. I have attached the project. I am saving data into two separate files, but I still have the problem when saving into one file only.

[G_Lo]

VPB,

I would try changing your analog input sample mode to Continuous instead of Finite.  I was not able to reproduce the behavior yet but this should make a difference if you would like to sample continuously.(i.e. no resetting)  Also, which version of Signal Express do you have? 

[VPB]

I am using Signal Express V2.5.1. I have tried continous samples and it will only run about an hour or two before an error is generated. I do not remember the error number, but it was something about samples not being available. Instead of saving to text files, I tried the "record" function, but that too only runs for a limited amount of time before it generates an error.  

[G_Lo]

VPB,

Was the error code 200016?  If so, this implies that you have a buffer underflow error (i.e. samples no longer available) This issue is usually caused by to slow of a sampling rate and this may be alleviated by making the rate faster.  Let me know if this is a wrong interpretation of the error.

[VPB]

I believe that that is one of the errors. Since I can only set the sampling rate with the Daq Assistant, which I have set to continuous @ 60HZ, and out comes continuous data from the 6009 module that I save to a file, what do I need to do?

[G_Lo]

Hi VPB,

The sampling rate represents how often the anlaog to digital conversion takes place per second, and the samples to read represents the number of samples the DAQmx Read VI retrieves each time from the PC buffer.  It seems that your sampling rate is not fast enough to keep up with samples being pulled off the buffer.  Each channel should have 2 samples available every 33ms (i.e. 2 / 60Hz) after the sampling has begun.  This time needs to be decreased to try to alleviate the issue.  I would suggest increasing your sampling rate but make sure not to make it that high or you may end up with a buffer overflow instead of an underflow.  Try increasing this rate and see what the results are.