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Stopping burst mode while it's running?


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#1 user1979

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Posted 09 January 2015 - 07:19 AM

Hello,

 

I am using Labview 2012 and a U6 module to measure  50 000 samples at 1000 Hz during 50 secs with the easy stream burst example. Is it possible to stop the U6 measurment at any time during the 50secs from a software point of view?

 

Thanks,

 

user79



#2 LabJack Support

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Posted 09 January 2015 - 08:27 AM

If you are going for more than a second or 2, you are usually better off using the normal stream technique where you read data once or twice per second in a loop.  With this technique you can stop the read loop whenever you want.  I would look at one of the other easy stream example VIs.

 

See Section 4.3.7 of the U6 User's Guide for a better understanding of how streaming works:

 

http://labjack.com/s...ers-guide/4.3.7



#3 user1979

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Posted 09 January 2015 - 09:34 AM

Thanks for your answer.

I need to count the time a signal is low over 50 secs and would like not to miss any short times the signal is low. This is why I am trying to avoid software timing by not starting new loops regulary and using the hardware timing.



#4 LabJack Support

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Posted 09 January 2015 - 10:15 AM

I am suggesting you still use stream mode.  What you are doing now:

 

Start Stream

Wait 50s

Read 50s of data

Stop Stream

 

When you just read 1 block of stream data like that, we call it stream-burst.  Instead you can do a normal stream:

 

Start Stream

While Keep Going

    Read 1s of data

Stop Stream

 

If you used that structure, and let the loop go 50 times, you will get the exact same data set as the burst method.  You will not miss scans.  The timing of each scan will be identical either way, is controlled by hardware, and is not impacted by software.



#5 user1979

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Posted 12 January 2015 - 01:45 AM

Thanks for your detailed answer. Looking at the print screen could you confirm this is what you advise me to do from a streaming point of view   ? (see attached print screen)

 

By the way, I guess the burst solution is only recommanded for high frequency measurement over a short period of time?

 

User



#6 LabJack Support

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Posted 12 January 2015 - 10:19 AM

No screen shot came through, but all you need to do is open and run the example "U6 easy Stream.vi".  It does exactly what I described.  You can stop it after 1 second or 50 seconds or whatever you want.  One change is that you probably want to add a shift register and concatenate the new data to an array each time so you can build up 1 big array with all the data.



#7 user1979

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Posted 13 January 2015 - 01:31 AM

Yes that's what I did.

 

Many thanks for your help.

 

user




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