Rockwell Automation 1756-HIST2G Historian ME 2.1 - Manual (Page 223)

A • F ACTORY T ALK H ISTORIAN ME R ULE E DITOR
213
FactoryTalk Historian ME ProcessBook trend with a vertical scale of database.
This attribute is not used for non-numeric points.

Step
Defines how numeric archived values are interpolated. The Step flag affects only
numeric points. The default behavior, OFF (0), treats archived values as a
continuous signal. Adjacent archived values are linearly interpolated. For
example, at 12:00:00, the value 101.0 is archived and at 12:01:00, the value 102.0
is archived. A request for the archive value at 12:00:30 would return 101.5.
Step ON (1) treats the archived values discretely. Adjacent archived values are not
interpolated; an archived value is assumed constant until the next archived value.
For example:
- At 12:00:00, the value 101.0 is archived.
- At 12:01:00, the value 102.0 is archived.
A request for the value at 12:00:30 would return 101.0.
In general, data coming from continuous signals should be archived in points with
the step flag OFF. Examples might include signals from thermocouples, flow
meters, etc. Data coming from discrete measurements should be archived in
points with the step flag ON. Examples are sampled laboratory data, batch charge
weight. In addition, the step flag affects the compression calculation. When it is
ON (1), a linear change of value greater than or equal to CompDev attribute
passes compression. This is essentially the same as the exception reporting. When
the step flag is OFF, the complete swinging door algorithm is applied.

Shutdown
Specifies whether the FactoryTalk Historian ME will automatically add a
shutdown event with the time stamp of the FactoryTalk Historian ME server
shutdown. In some cases, it is useful to record to FactoryTalk Historian ME points
when the archive was shut down to indicate a gap in the Data Collection.
Set Shutdown to ON (1) to record shutdown events for this data point (tag). The
default is ON.

Compressing
The FactoryTalk Historian ME uses compression specifications to filter the data
passed from the Snapshot subsystem to the Archive subsystem. The Snapshot
subsystem stores the most recent value for each data point. This most recent value
is called the Snapshot for that point. The Snapshot subsystem uses compression