ValueState retrieval query 6: querying state summary values

If state summary values are queried and the cycle boundaries match the summary periods, the ValueState calculations are supported and return valid results.

If state summary points are queried and the cycle boundaries do not match the summary periods, the ValueState calculations are supported, but they return DOUBTFUL (QualityDetail = 64) results.

State summaries are included in the cycle where the summary end time occurs. This causes results that do not match queries against the source tag and may cause inaccurate results, such as a total state time that is greater than the cycle time.

For example, this can occur if SysTimeSec is summarized with a state summary with one minute resolution, but then queried with 10 second intervals. In most of the retrieval cycles, there will be no values, but in the cycle that includes the summary end time (one in six of the retrieval cycles), all 60 states would be returned with each state having a state time of 1 second for a total of 60 seconds of state time in a 10 second retrieval cycle.