Rockwell Automation 1756-HIST2G Historian ME 2.1 - Manual (Page 308)

F ACTORY T ALK H ISTORIAN ME M ODULE U SER G UIDE
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Performance Equation
(PE)
An expression that allows a user to implement an arbitrary and
potentially sophisticated calculation without formal
programming. A performance equation has an intuitive syntax
and may consist of standard mathematical and logical
operators as well as a wide variety of built-in functions. The
result of a performance equation can be archived for a PE point
just like data for any other point.
Point A variable whose value is measurable and typically dynamic.
Examples include transmitter readings, status indicators,
manual inputs, control limits, etc. Each point must be assigned
a unique tag on the FactoryTalk Historian ME server, and
measurements of the point captured over time are effectively
stored as an array of timestamped values in the data archive.
Point Configuration The complete list of attributes characterizing a point.
Point Type The base attribute that specifies the data type for the values that
a point stores. The possible point types include the following:
int16, int32, float16, float32, float64, digital, string, and
timestamp. Point types can be edited after point creation, but
not all type transitions are allowed.
Project File The file that RSLogix 5000 software uses to store a controller’s
programming and configuration information. The file
extension must be .ACD; if you change the extension, the file
will not open.
Scan The base attribute that specifies whether or not the interface or
scanning program should collect new data for the associated
point. If Scan is disabled (set to 0), then new data will not be
collected.
Scan Class A specification that provides an interface with the schedule for
performing data collection for its associated points. The scan
class specification consists of a period and an optional offset.
The period determines the recurring interval when data
collection should occur, and the offset determines when data
collection should first start. A scan class can also optionally
contain a code to force the interface to use UTC time for
scheduling. A point can only be in one scan class.
Term Definition