Selecting values for analog summary tags (wwValueSelector)
- Last UpdatedFeb 07, 2025
- 4 minute read
For an analog summary tag, multiple summarized values can be stored in the historian for a single summarization period. When you query analog summary data, a single value, time, and quality (VTQ) must first be extrapolated from the summarized values.
You set the value selector in the query to specify which summarized value to return. The possible values are as follows:
|
Value Selector Setting |
Value Returned |
Timestamp Returned |
|---|---|---|
|
AUTO |
The retrieval mode determines the value. See the following table for how AUTO applies to the value selection. This is the default value. |
The retrieval mode determines the timestamp. See the following table for how AUTO applies to the value selection. This is the default value. |
|
FIRST |
The first value that occurs within the summary period. |
The actual timestamp of the first value occurrence within the summary period. |
|
LAST |
The last value that occurs within the summary period. |
The actual timestamp of the last value occurrence within the summary period. |
|
MIN or MINIMUM |
The first minimum value that occurs within the summary period. |
The actual timestamp of the first minimum value occurrence within the summary period. |
|
MAX or MAXIMUM |
The first maximum value that occurs within the summary period. |
The actual timestamp of the first maximum value occurrence within the summary period. |
|
AVG or AVERAGE |
A time-weighted average calculated from values within the summary period. |
The summary period start time. |
|
INTEGRAL |
An integral value calculated from values within the summary period. |
The summary period start time. |
|
STDDEV or STANDARDDEVIATION |
A standard deviation calculated from values within the summary period. |
The summary period start time. |
The following table describes the value to be considered if the value selector is set to AUTO:
|
Retrieval Mode |
Analog Summary Behavior |
|---|---|
|
Cyclic |
The last value within the summary period is used. The actual timestamp of the last value occurrence within the summary period is used. |
|
Delta |
The last value within the summary period is used. The actual timestamp of the last value occurrence within the summary period is used. |
|
Full |
The last value within the summary period is used. The actual timestamp of the last value occurrence within the summary period is used. |
|
Interpolated |
The retrieval mode determines the appropriate value to return. See the following table for how AUTO applies to the value selection. This is the default value. |
|
Best Fit |
The first, last, min, and max points from analog summaries are all considered as analog input points. Best fit analysis is done with these points. If the analog summary percentage good is not 100%, the cycle is considered to have a NULL. |
|
Average |
The averages of analog summaries are calculated using the values from the Average column of the AnalogSummaryHistory table. Interpolation type is ignored for analog summary values, and STAIRSTEP interpolation is always used. PercentGood is calculated by considering the TimeGood of each analog summary. If cycle boundaries do not exactly match the summary periods of the stored analog summaries, the averages and time good are calculated by prorating the average and time good values for the portion of the time the summary period overlaps with the cycle. Quality will be set to 64 (uncertain) if cycle boundaries do not match summary periods. If the QualityDetail of any analog summary considered for a cycle is uncertain (64), the resulting quality is set to 64. |
|
Minimum |
The first minimum value within the summary period is used. The actual timestamp of the first minimum value occurrence within the summary period is used. |
|
Maximum |
The first maximum value within the summary period is used. The actual timestamp of the first maximum value occurrence within the summary period is used. |
|
Integral |
The integrals of analog summaries are calculated using the Integral column of the AnalogSummaryHistory table. Interpolation type is ignored for analog summary values, and STAIRSTEP interpolation is always used. PercentGood is calculated by considering the TimeGood of each analog summary. If cycle boundaries do not exactly match the summary periods of the stored analog summaries, the integrals and time good are calculated by prorating the integral and time good values for the portion of the time the summary period overlaps with the cycle. Quality is set to 64 (uncertain) if cycle boundaries do not match summary periods. If the QualityDetail of any analog summary considered for a cycle is uncertain (64), the resulting quality will be set to 64. |
|
Slope |
The last value within the summary period is used. The actual timestamp of the last value occurrence within the summary period is used. |
|
ValueState |
Cannot be used with analog summary data. No values are returned. |
|
Counter |
Cannot be used with analog summary data. No values are returned. |
|
RoundTrip |
Cannot be used with analog summary data. No values are returned. |
For an analog summary tag, if any of the data within a summary period has an OPCQuality other than Good, the OPCQuality returned will be Uncertain. This is true even for summary values that are not calculated, such as first, last, minimum, maximum, and so on. For example, if the OPCQuality for a last value is actually Good, but there was a I/O Server disconnect during the summary calculation period, the OPCQuality for the last value is returned as Uncertain. A QualityDetail of 202 is used to distinguish between the original point and the latest point. (Note, however, that replicated data may show a QualityDetail of 202 for points other than the latest point.)