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Stormwater sampling system data gap /blackout period upon triggering


KMH Dec 9, 2019 11:17 AM

Hi all, I'm running a stormwater sampling project which connecting CR800 to an ISCO 3700 sampler, an ISCO 2150 flow module, and a tipping bucket rain gauge. I got a program from vendor which is working fine except 1 thing: there will be a 3-4 minutes data gap (or blackout period) right after the first sampling in ISCO sampler is triggered by C port where no data from flow module and rain gauge is recorded, not even timestamp. This only happens to first sampling, and the last sample if continuous sampling triggered to stop due to triggering value lower than threshold (in this case I using water level reading from flow module). All the subsequent sampling preset to 4 minutes interval are working fine. Did anybody experiencing the same situtation or able to help me? Thank you very much.


JDavis Dec 9, 2019 01:16 PM

Look in your Status table to see if you are getting skipped scans. Your program may be taking longer to complete everything that scan, than what your scan rate is.


KMH Dec 10, 2019 11:28 AM

Hi JDavis,

Thank you so much! Indeed the status showing some skipped scan as below:

"   Program Errors

     Skipped Scans: 10060 - The main scan interval or number of scan buffers may need to be increased.

     Skipped Slow Scans: (1): 0

     Skipped Slow Scans: (2): 3 - The main scan interval or number of scan buffers may need to be increased.

     Skipped System Scans: 85 - The main scan interval or number of scan buffers may need to be increased.

     Variable Out of Bounds: 0"

Then I looked into the program script and found possible parts like this:

SlowSequence
  Scan (60,Sec,0,0)  ' Get the ISCO AV Measurement
  If AV_ReadyToSample = TRUE Then
   AV_ReadyToSample = FALSE
        EndIf    NextScan  
EndSequence

or something like this.

'Scheduler for disable/enable trigger
SlowSequence    Scan (1,Min,0,0)

  RealTime( rTime )

NextScan 

Does the SlowSequence means that the scanning will be relatively slow? And what does Scan(1,Min,0,0) indicates?

Thank you so much for your support.


JDavis Dec 11, 2019 09:43 AM

The 2150 takes a long time to measure. You can look at values in your Status table for MeasureTime and MaxProcessTime. The time units for those values are microseconds. Add the two values together, and it will provide a good indication on how much you need to slow down the scan rate.


KMH Dec 12, 2019 08:31 AM

Hi JDavis, the MeasureTime is 1500ms and MaxProcessTime is 10874855ms, which total up is 10.876355 seconds. Another system showing total of 6.229503 seconds. So I need to slow down the scan rate instead of speed up the scan rate? How do I slow down the scan rate? Is the part mentioned earlier (SlowSequence
  Scan (60,Sec,0,0)  or (SlowSequence    Scan (1,Min,0,0)) indicate the scan rate?

Thanks again for your help.

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