Question about compress records

["Guyotte, Greg via Tech-talk" <tech-talk at aps.anl.gov>]

Hello,

 

I’m attempting to use a pair of compress records to calculate the average of a scalar PV over a window of time.

 

The first compress record is the “Circular Buffer”, which has a size of 360 samples, with a SCAN period of “10 second”, thereby sampling the scalar PV (which is INP) over one hour of time.

 

record(compress, “Buffer”) {

  field(INP, “Current”)

  field(ALG, “Circular Buffer”)

  field(NSAM, “360”)

  field(SCAN, “10 second”)

  field(FLNK, “AvgCurrent”)

}

 

The second compress record is set to “N to 1 Average”, taking as INP the array obtained from the circular buffer compress record.  This record should process each time the circular buffer receives new data, therefore the circular buffer record has a forward link to this record:

record(compress, “AvgCurrent”) {
  field(SCAN, “Passive”)

  field(INP, “Buffer”)

  field(ALG, “N to 1 Average”)

  field(N, “360”)

}

 

What I find is that the “N to 1 average” record is invalid until the Circular buffer has filled up (e.g. after one hour in my case).  After the circular buffer is full of samples, it works as expected.

 

I have also tried to compute the average with an acalcout record, but I got the same result.

 

Is this the expected outcome, or can anyone suggest how to implement so that average works before the circular buffer is full?  Is there perhaps a way I can initialize the circular buffer?

 

Thanks,

Greg Guyotte