About rate-of-change (ROC) alarms at runtime

When the Attribute is set to NaN, the following occurs:

• The quality of the Rate attribute is set to UNCERTAIN.

• The value of the Rate attribute will remain unchanged until it receives a value quality of GOOD.

Limit checking for each ROC alarm is as follows.

• If the rate evaluation period has expired, then calculate the Rate as:

  • (Attribute value - last Attribute value) / (current time - last time)

  • convert Rate to target units (sec, min, hour or day)

• If Rate < DecreasingHi.Limit, then set the DecreasingHi condition. Else, clear the DecreasingHi condition.

• If Rate > IncreasingHi.Limit, then set the IncreasingHi condition. Else, clear the IncreasingHi condition.