How are average values calculated in Infinity Trend Logs.

Issue

How does Continuum calculate the average value when a point is configured with an Average LogType.

Product Line

Andover Continuum

Environment

  • Log
  • TrendI
  • Infinity Controller
  • NetController
  • CX
  • i2
  • TCX
  • SCX

Cause

It is often important for the end user to know how log values are calculated in cases where trend log data may be audited.

Resolution

  • Point values are sampled stored and calculated at the controllers level, not at the Cyberstation level. 
  • The point logging process is not dependent on the scan time of the controller and is therefore unaffected by a controllers scan time.
  • The controller stores the most recent data polled as its data sample.
  • The smallest interval that we can log data is 1 second.  Even when an average log type is selected, a log with a 1 second interval is essentially a non averaged log since each calculation would take one sample/second and divide it by interval in seconds (1).
  • With points logged with an average log type at intervals that are > 1 second, each second the most recent data sample added to the summed value.
  • The sample values are added together, (each new sample is added to the stored sample value) and the sum is divided by the number of samples taken (which would also equal the number of seconds in the log interval). 
  • A controller calculates average point values using a weighted average algorithm at the end of the log interval period.
  • A controller does not retain data samples when the log period ends, but rather it begins to assemble a completely new collection of sample data at the start of each interval period.