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Almuf
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I use write to meas. Express vi to get Data out of cRIO but it is so slow. Why?

Hi All.

 

I use Labview 2011 to control my thermal loop. So we have several thermocouples, pressure transducers, valves etc... For now, I don't have a problem with controlling and displaying the values but whenever I ask to get data, program slows down and I am not able to get data faster than 750ms. which I find is so slow. I should be able to get at least 200ms (which is not fast either but it is enough for us). I try to write measurements from several channel ( right now 53 channels) and I use write to measurement file express vi.

 

I made a small test program to see if my main program is so heavy or not. In this test program, I scanned 32 channel in NI9205 and tried to write the measurement with 100ms without displaying and I am still not able to write at that speed.

 

So, am I not able to configure correctly the scan engine of cRIO9074 or Write to measurement express vi is always slow ?

 

Thank you,

 

altan

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Cameron-T
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Re: I use write to meas. Express vi to get Data out of cRIO but it is so slow. Why?

Can you attach the test program so we can see how you have things set up?

Cameron T
Applications Engineer
National Instruments
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Almuf
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Re: I use write to meas. Express vi to get Data out of cRIO but it is so slow. Why?

Here is the test program with Write to Measurement File Express Vi.

 

Eventhough i ask 100ms, i am not able to write faster than 400ms with this set up. In my main code, i have 3 NI9205, NI9263 and NI9265 so I have many indicators. When i add all, code becomes heavy and i can't write faster than 750ms.

 

Instead of using Express Vi, i modified my main code using TDMS Open/Write/Close functions. With that i tried and able to write at 100ms which is enough for me. But i am not able to close the file so i can not change the file name and press save button so get another set of data. It adds(append) new data into the first file.

 

Thanks in advance.

 

altan

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Cameron-T
Posts: 121
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Re: I use write to meas. Express vi to get Data out of cRIO but it is so slow. Why?

Altan,

 

Writing to a file is not deterministic. That is why you are not getting the performance you are expecting. It would be a good idea to queue the data you want to write to a file and dequeue and write it in a regular loop. Try to keep only deterministic functions in a Timed Loop and keep nondeterministic functions in regular loops. Hope this helps.

Cameron T
Applications Engineer
National Instruments