Rockwell Automation FactoryTalk Historian SE 3.0 H2H Interface User Guide - Manual (Page 19)

FactoryTalk Historian To Historian Interface User Guide 13
source point ID and the search ends. Otherwise, proceed to the step 4. If the search
ends in this step and either the
UserInt1 attribute is not greater than zero or the
interface is configured for source Historian Server-level failover, the interface rejects
the point.
4. The source point tag name is the same as the receiving tag name.
The search for the source point ends with either a source tag name or source point ID. If the
source tag name or point ID does not exist, the interface puts the point into an error state and
logs a message.
Note: The PItoPI APS Connector contains a separate implementation of the search
for source point tag name or ID. If an interface instance is registered with APS,
confirm that the PItoPI APS Connector version implements the same search
procedure as the interface, which is required to ensure that the PItoPI APS
Connector synchronizes with the same source point as the interface. If the latest
release of the PItoPI APS Connector is older than this version of the FactoryTalk
Historian to Historian interface, compare the procedure described in this section with
the “How PItoPI and PItoPI_APS Find Source Points” section in the Historian to
Historian TCP/IP Interface AutoPointSync Connector user manual.
Data Collection
There are two modes of data collection, history recovery and scanning for updates. History
recovery enables users to recover archive data for time periods when the interface was not
running or otherwise unable to collect data. After performing history recovery, the interface
begins scanning for updates. When the interface is scanning for updates each tag recei
Historian to Historian TCP/IP Interface AutoPointSync Connector ves an incremental copy of
either archive or exception data from its configured source tag.
A tag configured for exception data receives a copy of its source tag‟s current value updates.
A tag‟s current value is also referred to as its snapshot value. A snapshot value is a data event
that has passed the first level of data filtering, the exception test. Every Historian Server
maintains a snapshot table that contains the current value for each tag in its database. When a
new value passes exception filtering, the snapshot table is updated. The existing snapshot
value is then subjected to the compression test. The compression test determines whether or
not a snapshot value is archived. If a value passes compression filtering, it becomes part of
the archive data collection.
Tags are configured for archive or exception data collection through scan class assignment.
Scan classes are update rates that users define in the interface startup configuration file. When
a scan is executed the interface performs an incremental copy of data for each tag in its scan
list. By default, all tags assigned to the first scan class receive exception data. Tags assigned
to any other scan class receive archive data.
Note: Interface performance is maximized when a separate copy of the interface is
used for archive and exception data collection.
All data collected by the interface has already passed exception filtering on the source
Historian Server. Any additional exception filtering can only lead to a data mismatch between
Historian Servers. Additionally we recommend applying source tag compression deviation
settings to interface tags. See the section
Exception and Compression for additional
information.