Resample step is discontinuous

[OHP]

I am collecting 24 channels of temperature data and 4 channels voltage data into an SCXI-1303 and SCXI-1327.  One thousand samples of data are collected continuously at 1000 Hz.  This high requency is necessary for the voltage channels which go through Amplitude and Levels and Tone Extraction steps.  Only 100 Hz of temperature data is necessary, therefore, that data is run through the Subset and Resample step.  The problem is that when the data is resampled at 100 Hz, it leaves off a few data points at the end of each iteration.  This adds up to about a 20 second of missing data after 5 minutes of collected temperature data.  Is there a way to correct this?  Is the step being overloaded with 24 temperature channels?  I have tried all availible resample options in Subset and Resample step and all of them result in this error.

[mallorim]

Hi OHP,

I am not sure about why you are losing this data, but I did want to ask if the data you did acquire from the thermocouples was correct? Sometimes, when you sample from a number of thermocouples and votlages at that high a rate, you can build up voltages on the Analog to Digital Converter (ADC) that don't have time to properly dissipate. This will cause a repeated error in your temperature measurement. Before we go about trying to troubleshoot a problem specific to data acquisition at that high rate, I would recommend verifying that your temperature measurements are valid when sampling at such a high speed.

Regards,

Mallori

[OHP]

The temperature data is correct before it is resampled.  I just ran a test to confirm this and I found something interesting.  I was collecting data from 24 thermocouples at 1000 Hz and the number of "samples to read" was set to 1000.  I was resampling the temperature data from the 24 thermocouples down to 100 Hz.  I recorded both the 1000 Hz and 100 Hz data to the hard drive.  After collecting data for 28 seconds, the 1000 Hz data had 28000 samples and the first thermocouple in the 100 Hz data had 2800 samples.  This is what should happen.  However, the 23 other thermocouples resampled to 100 Hz only had 2772 samples, this is 28 missing samples.  So, the first thermocouple is resampled correctly, but the others loose 1 sample every second.  When I change the number of "samples to read" to 2000, therefore it's resampling 2 seconds worth of data, it is missing 14 samples.  Therefore, it looses 1 sample every 2 seconds.

 I believe the resample step is dropping the last value each iteration.  It works correctly if I am only resampling one channel, but when I resample more than one channel per step, it drops the last value of each iteration.

Does anyone know if there is a way to fix this? or should I post this as a bug?

[John_P1]

Hi OHP,

Thanks for posting!  I have been unsuccessful so far in my attempts to recreate the issue you are experiencing.  However, I am simply monitoring the channel of a DAQ device (no SCXI chassis immediately handy).  Which SCXI modules are you using (underneath the 1303 and 1327)? 

I think the problem may be related to the way that the channels are multiplexed on SCXI in relation to how the Subset and Resample step is defined.  Once we are able to recreate the problem over here we can start looking into possible workarounds, this sounds like a likely bug specific to the interaction between SCXI and the Subset and Resample step.  As soon as you can please let us know which modules you are using so we can continue to look into the matter further.  Thanks and have a great day!

-John 

[OHP]

The SCXI-1303 is attached to the 1102 and the 1327 is attached to the 1121.  The SCXI-1000 is connected to the computer via the SCXI-1600 USB module.

Thanks for the help

[John_P1]

Hi OHP,

After tracking down the hardware, I still can't seem to reproduce your results.  Could you post your seproj file so I can try running the code exactly as you have configured it? 

I ran a thermocouple task (1000 samples at 1kHz) on the 32 channels of the 1102 without running into this issue when logging the data to an ASCII file.  Each iteration of the code gave me 100 samples after using the Subset and Resample step.  Any additional information about how you have your task set up would be helpful.  Thanks!

-John 

[OHP]

I apologize for taking so long in getting back to you.

I determined it has something to do with my computer.  I was able to build the same seproj file on another computer.  On that computer, Signal Express collected the data without any errors.  Also, the seproj file on my computer is much larger than the file created on the other computer.  Also, I was not able to run the original seproj file on the new computer.  I have not been able to figure out the cause beyond that.

Attached are the two files.  Test_v3.seproj is from the original computer (i.e. results are incorrect).  Test_v3_rewrite_2.seproj is from the new computer.

Thank you for your help.