RoundTrip retrieval - query examples

To use the RoundTrip retrieval mode, set the following parameter in your query:

wwRetrievalMode = ‘RoundTrip’

The following queries compare the results between ValueState retrieval and RoundTrip retrieval.

This first ValueState retrieval query returns the average amount of time that the 'Reactor1OutletValve' tag is in "on" state and the average amount of time it is in the "off" state for a single cycle. Any state changes that occur across the cycle boundaries are not included.

SELECT DateTime, vValue, StateTime

FROM History

WHERE TagName IN ('Reactor1OutletValve')

AND DateTime >= '2009-09-16 12:35:00'

AND DateTime <= '2009-09-16 12:55:00'

AND wwRetrievalMode = 'ValueState'

AND wwStateCalc = 'AvgContained'

AND wwCycleCount = 1

The results are:

The first two rows are for the "phantom" cycle leading up to the query start time and have a timestamp of the query start time.

The second two rows show the average amount of time for each state and have a timestamp of the query end time (the default).

Compare these results to same basic query that instead uses RoundTrip retrieval:

SELECT DateTime, vValue, StateTime

FROM History

WHERE TagName IN ('Reactor1OutletValve')

AND DateTime >= '2009-09-16 12:35:00'

AND DateTime <= '2009-09-16 12:55:00'

AND wwRetrievalMode = 'RoundTrip'

AND wwStateCalc = 'AvgContained'

AND wwCycleCount = 1

The results are: