CALCARCHEXPR action

Function
 The action performs a calculation of specific expression over historical values. Historical values are expressed through the names of historical objects in the expression.


Declaration


CALCARCHEXPR archExprIdent_Txt, btIdent_TimA, etIdent_TimA, stepIdent_Int, _ignoreInvalid_Bool, _locVarColValueIdent_Rec, statusIdent_Int[, archivInstance_Int]
Parameters
archExprIdent_TxtinValue identifier of Text type containing the expression.
btIdent_TimAinIdentifier of AbsTime type - interval beginning.
etIdent_TimAinIdentifier of AbsTime type - interval end.
stepIdent_IntinIdentifier of Int type - time step [s].
_ignoreInvalid_BoolinIdentifier of Bool type - invalid values in expression will be replaced by 0.
_locVarColValueIdent_RecoutReference to a local variable column of RECORD type - final values.
statusIdent_IntoutIdentifier of Int type - the success of calculation.
archivInstance_IntinOptional identifier of Int type - identification of archive instance. If the parameter is not defined, the value 0 will replace it.
Description
 The action performs a calculation of specific expression over historical values. Historicalvalues are expressed through the names of historical objects in the expression.

The rules of this calculation are identical to the calculation rules mentioned in definition of calculated historical value.

If a structured archive is used in an expression, a zero [0] number of row cannot be used.

The calculation is performed for specified time period <btIdent_TimA, etIdent_TimA>.

If parameter stepIdent_Int
= 0 - it means the calculation for change => each change some of the source data (archived) causes the entered expression recount and relevant value will be in result. ≠ 0 - it means the periodic calculation => the entered expression is evaluated in periods btIdent_TimA, btIdent_TimA+1*stepIdent_Int, btIdent_TimA+2*stepIdent_Int .... Resultant value array is written into entered column of local structured variable _locVarColValueIdent_Rec (variable can be dimensioned again).
Notes

Note 1: The expression must contain the name at least one of historical value.

Note 2: If the expression contains several historical values, they all must have the same parent in terms of DODM (ARC process).

Note 3: The CALCARCHEXPR action does not apply the time constraint that is active when calculating evaluated historical values and that does not allow calculation for times in the future. Using the CALCARCHEXPR action, it is therefore possible, for example, to calculate an expression over a script-filled historical values that also have data in the future.

Example
 TIME _bt, _et
 INT _step
 INT _retCode
 TEXT  _expr
 TEXT _err
 BOOL _bIgnoreInvalid
 RECORD NOALIAS (SD.Data) _data
 
 _bt := %StrToTime("00:00:00 01-01-2008")
 _et := %StrToTime("00:00:00 02-01-2008")
 _step := 1
 _bIgnoreInvalid :=  @TRUE
 _expr :=  "H.a + H.GetArchRowCol_Ref[2]^I2 + H.GetArchRowCol_Ref_Col_I1[2]"
 
 CALCARCHEXPR _expr, _bt, _et, _step, _bIgnoreInvalid, _data^Value, _retCode
  
 IF _retCode =  _ERR_NO_ERROR THEN
   ; processing of result
 ELSE
   _err :=  _ERR_MSG ; extended error description
 ENDIF

Owing to the expression parsing works during system running (not during configuration) and if any errors occur, it is possible to obtain their detailed description as value of predefined local variable of Text type _ERR_MSG.

Related pages:

Script actions

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