TDMS File starts recording data at 20Hz, but after a short time drops to <10Hz as VI slows, why?

[BowenM]

One option that I have done before was write a FIFO buffer as an action engine.  I stored about 1/2 hour of data in the buffer always, with  "Add Data", "Read New Data", and "Read Historic Data" commands.    I could then have my data save loop run at a very slow rate with automatic bunching, with the added option of recovering / saving 1/2 hour worth of data if ever needed.

[superomario]

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@crossrulz wrote:

If you are using a Producer/Consumer, it is very easy.  One way is to recieve multiple elements in your queue and then write all of them in a single TDMS write.

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Aren't I doing that now in the code I posted? I have a cluster of elements the queue, are you saying lose the other two writes, and recmombine them later? This is the code i posted earlier that is slowing down: 

[crossrulz]

Yes.  So with your top loop, put the dequeue inside of a FOR loop that can stop when there is a timeout.  The reason for the FOR loop is to log multiple instances at once.  I would set N to be something like 10 (or more if you can afford to wait longer between writes).

[crossrulz]

And looking at this code again, we should combine the two string writes into a single write, like we are doing with the numerics.

[superomario]

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@crossrulz wrote:

And looking at this code again, we should combine the two string writes into a single write, like we are doing with the numerics.

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How do I combine them but keep them appearing in the right columns like they are now? I made them separate since I needed the headers to appear in excel a certain way when I opened the TDMS in excel.

Also am I doing a best practice by having double queues, one for VISA and one for data? Should I move the VISA just into the main loop with all the graphing? would that save memory/prevent slow downs?

And did i implement the array preallocation correctly in the main graph?

[crossrulz]

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@superomario wrote:

How do I combine them but keep them appearing in the right columns like they are now? I made them separate since I needed the headers to appear in excel a certain way when I opened the TDMS in excel.

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Well, if that is a requirement, then nevermind.

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@superomario wrote:

Also am I doing a best practice by having double queues, one for VISA and one for data? Should I move the VISA just into the main loop with all the graphing? would that save memory/prevent slow downs?

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That is what I do.

[superomario]

Thanks, I will give the for loop a try and run the program again, if it still does not result in 20sample/sec data recording/display am I just SOL?

And when you say that is what you do, do you mean keep two queues or VISA in main loop?

[crossrulz]

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@superomario wrote:

And when you say that is what you do, do you mean keep two queues or VISA in main loop?

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I have what I call "modules".  In your case, there is an instrument module, a processing module, and a logging module.  Communication between loops is done with queues, just like what you have now.

[superomario]

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@crossrulz wrote:

Yes.  So with your top loop, put the dequeue inside of a FOR loop that can stop when there is a timeout.  The reason for the FOR loop is to log multiple instances at once.  I would set N to be something like 10 (or more if you can afford to wait longer between writes).

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How did you get the stop sign in the for loop? Nvm I got that.

I am getting the error REfnum became invalid while the node waited for it. if the for loop is in the code and i hit the stop button. what does that mean?

[crossrulz]

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@superomario wrote:

I am getting the error REfnum became invalid while the node waited for it. if the for loop is in the code and i hit the stop button. what does that mean?

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Well, you are trying to stop this loop by destroying the queue.  So that makes sense to me.