You need to use historic functions to specify which historic values are used by your program. Each historic function requires values for its arguments (as shown below). You have to include each argument when you use a historic function in an ST program or Function Block Diagram.
The arguments include StartTime and EndTime which define a time span, RecordIdx which is the number used to identify one historic value, and Forward which is used to instruct the program to move through a series of historic values. Forward arguments can have values of True or False (True means proceed forward to the next historic record; False means proceed backwards to the previous historic record).
You will need to use the following information when using a historic function:
| Function | Arguments |
Returns |
|---|---|---|
|
RawCount |
StartTime, EndTime |
The number of values between the StartTime and EndTime |
|
RawValue |
StartTime, EndTime, RecordIdx, Forward |
Value between StartTime and EndTime at RecordIdx |
|
RawTimeStamp |
StartTime, EndTime, RecordIdx, Forward |
Time value between StartTime and EndTime at RecordIdx |
|
RawQuality |
StartTime, EndTime, RecordIdx, Forward |
Quality value between StartTime and EndTime at RecordIdx |
|
RawQualityDesc |
StartTime, EndTime, RecordIdx, Forward |
Quality description between StartTime and EndTime at RecordIdx |
|
RawCountRange |
StartTime, Interval |
The number of values between StartTime and StartTime+Interval at RecordIdx |
|
RawValueRange |
StartTime, Interval, RecordIdx, Forward |
Value between StartTime and StartTime+Interval at RecordIdx |
|
RawTimestampRange |
StartTime, Interval, RecordIdx, Forward |
Value between StartTime and StartTime+Interval at RecordIdx |
|
RawQualityRange |
StartTime, Interval, RecordIdx, Forward |
Value between StartTime and StartTime+Interval at RecordIdx |
|
RawQualityDescRange |
StartTime, Interval, RecordIdx, Forward |
Value between StartTime and StartTime+Interval at RecordIdx |
|
ProcessedValue |
StartTime, EndTime, AggregateId |
Historic value between StartTime and EndTime using AggreagteId. |
For a list of the historic algorithms that are available, see OPC Historic Aggregates (Algorithms) in the ClearSCADA Guide to Expressions.
Further Information