RoundTrip retrieval

RoundTrip retrieval is very similar to ValueState retrieval in that it performs calculations on state occurrences in the within a cycle period you specify. However, ValueState retrieval uses the time spent in a certain state for the calculation, and RoundTrip retrieval uses the time between consecutive leading edges of the same state for its calculations.

You can use the RoundTrip retrieval mode for increasing the efficiency of a process. For example, if a process produces one item per cycle, then you would want to minimize the time lapse between two consecutive cycles.

The RoundTrip mode returns a row for each state in any given cycle. RoundTrip retrieval only works with integer analog tags, discrete tags, and string tags. If real analog tags are specified in the query, then no rows are returned for these tags. RoundTrip retrieval is not applied to state summary or analog summary tags. NULL values are treated as any other distinct value and are used to analyze the round trip for disturbances.

RoundTrip retrieval is supported for the History and StateWideHistory tables.

Any point on the boundary of the end cycle will be considered to the next cycle. The point on the boundary of the end query range is not counted in the calculation except that it is used to indicate that the previous state is a contained state.

If no roundtrip state is found within the cycle for a supported tag, a NULL StateTime value is returned. If there is no valid point prior to the phantom cycle, a NULL state is returned for the phantom cycle.