Rockwell Automation 1756-HIST2G Historian ME 2.1 - Manual (Page 113)

6 • C OLLECTING D ATA
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The exception algorithm relies on the following parameters:
ExcMax Sets a limit on how long the Data Collection service can go
without reporting a value to the FactoryTalk Historian ME
server. After the ExcMax time period, the Data Collection
service sends the next new value to the FactoryTalk Historian
ME server, regardless of whether the new value is different from
the last reported value.
Note that the time between exception reports might be greater
than the exception maximum time if no new values are received
by the Data Collection service for a point. Neither the
FactoryTalk Historian ME server nor the Data Collection service
will 'create' data.
ExcMin Sets a limit on how frequently the Data Collection service can
report values. For example, if you want the Data Collection
service to wait a full ten minutes before reporting a new value to
the FactoryTalk Historian ME server, then you would set the
ExcMin attribute to ten minutes.
Parameter Description
Exception
Maximum
The maximum time span between exceptions, expressed in
seconds. This value is configured for each point in the ExcMax
attribute.
Exception
Minimum
The minimum time span between exceptions, expressed in
seconds. This value is configured for each point in the ExcMin
attribute.
ExcDev
(also called
Exception
Deviation
)
The deadband when exceeded causes an exception. This is
configured for each point in either the ExcDev or
ExcDevPercent attribute.
OldEvent The value/status/timestamp of last event sent to the Snapshot.
This is the last event that passed exception report.
PrevEvent The value/status/timestamp of last event compared to determine
whether or not to send to the Snapshot.
Field Description