TimeStamp rule (wwTimeStampRule)

For various cycle-based retrieval modes, you can control whether the returned values are timestamped at the beginning or at the end of each cycle.

To force a query to timestamp results at the start of a cycle, specify the following in the query:

AND wwTimeStampRule = 'Start'

To force a query to timestamp results at the end of a cycle, specify the following in the query:

AND wwTimeStampRule = 'End'

If you include the wwTimeStampRule column in your SELECT statement, it will show which timestamp rule has been applied for the individual row, if applicable.

The options are as follows:

• Start: The value for a given cycle is stamped with the cycle start time. For example, in the following illustration of a cyclic query, the following values are returned at the cycle boundaries:

  • At TC0: P7, because it falls on the cycle boundary. In cyclic mode, if there is a value right on the cycle boundary, it is considered to belong to the cycle before the boundary. In this case, this is the cycle starting at TC0 and ending at TC1, and because the Start timestamp rule is used, the value is timestamped at TC0.

  • At TC1: P11, because it is the last value in the cycle starting at TC1 and ending at TC2

  • At TC2: The last value in the "phantom" cycle starting at TC2

    

• End: The value for a given cycle is stamped with the cycle end time. For example, in the following illustration of a cyclic query, the following values are returned at the cycle boundaries:

  • At TC0: P1, because it is the last value in the "phantom" cycle ending at TC0. Because the End timestamp rule is used, the value is timestamped at TC0.

  • At TC1: P7, because it falls on the cycle boundary. In cyclic mode, if there is a value right on the cycle boundary, it is considered to belong to the cycle before the boundary. In this case, this is the cycle starting at TC0 and ending at TC1, and because the End timestamp rule is used, the value is timestamped at TC1.

  • At TC2: P11, because it is the last value in the cycle ending at TC2

    

• Server default: Either Start or End is used, depending on the system parameter setting on the AVEVA Historian.

This option is relevant in the following retrieval modes:

• Cyclic retrieval (AVEVA Historian 9.0 and later)

• Interpolated retrieval

• Average retrieval

• Integral retrieval

• Counter retrieval

• ValueState retrieval

• RoundTrip retrieval