Specific value detectors

Two specific value detectors are available:

• Analog specific value detector

• Discrete specific value detector

These detectors can be used to detect if a historical tag value matches the state defined by the detector criteria. For the criteria, historical values are compared to a target value that you specify. If a value matches the criteria, then an event is logged into the EventHistory table, and any associated actions will be triggered. For example, an analog specific value detector could be configured to detect if the value of 'MyAnalogTag' was ever greater than 1500. Likewise, a discrete value detector could be configured to detect if the value of 'MyDiscreteTag' was ever equal to 0.

For a specific value detectors, you can apply either edge detection or a resolution to the returned data. The resolution is used only when the edge detection is set to NONE (in which case the retrieval mode is cyclic). For more information, see these topics from the AVEVA Historian Retrieval Guide:

• Resolution (values spaced every X ms) (wwResolution)

• Edge detection for events (wwEdgeDetection)