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analog input (NI 9236) offsets occur when writing intermediate files on cRIO

Configuration:  cRIO (9014, 9104), Labview 8.6, one NI 9236 Strain gage module

 

I have a modified version of NI 9236 Getting Started.lvproj that records continuously.  In my host vi, the data from the FIFO is continually added to a primary array and at specified

intervals, this array gets passed to a case structure where the appropriate sub-array is stripped and sent to a write-to-txt file.  The process works, however, depending on the

size of the sub-array requsted for output, the cRIO introduces offsets into the signals (different amounts on different channels). 

 

For example, I started out requesting output after every 12000 iterations(so my su-array would be 12000 x 8 ), and once the first write procedure occurred, the offsets were introduced.  I then backed down from 12000 to 2000 and again the offsets were introduced but only after several (maybe 11) successful write procedures. 

 

I have tried to re-initialize the primary array after every write procedure to keep the primary array size small and to avoid the overhead of trying to find the appropriate starting point but still no luck.

 

Any suggestions out there? Thanks for any assistance.

 

 

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Hello,

 

I am confused by how much offset you are seeing in your system. Could you provide an example of the offset? Thanks.

 

 

National Instruments
RIO Embedded Hardware PSE

CompactRIO Developers Guide
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The offsets vary by channel, but are fairly consistent with each occurrence.  They range from +/-1000 micro-strain to +/-20,000.  I have attached a screen shot

for reference.

 

In the meantime, I have found a work around.  I modified the code to exit the acquire loop after each write procedure, then re-start the acquistion.  I guess this allows

the cRIO to reset in some way without causing the signal offsets.  The only downside is that I lose a bit of data during the write.

 

 

Darin

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Now for the attachment....
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Hello,

 

I will take a look at your code offline, however, do you just do lead wire compenation once or do you do it multiple times?

National Instruments
RIO Embedded Hardware PSE

CompactRIO Developers Guide
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I apply the shunt calibration to check the lead wire correction factors (which are normally around 1), prior to acquiring measurements. However I have not been applying the lead wire correction

factors to the measured data.

 

 

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