Event detectors

Each event tag must have an associated event detector. An event detector is a mechanism for determining when the set of event criteria for an event tag has been satisfied. When you configure an event detector, you must first configure its type and then configure the parameters associated with that detector type. You can choose from the following types of event detectors:

• SQL-based detectors

• Schedule detectors

• External detectors

The generic SQL, analog specific value, and discrete specific value detectors are SQL-based detectors. The schedule detector is a time-based detector. The external detector is used when triggering an event by the ActiveEvent ActiveX control.

For all detectors, the Classic Event subsystem will initially base the query for data in history at the time the Classic Event subsystem starts. Subsequently, the Classic Event subsystem will base the query on the last successful detection; that is, the time of the most recent detection becomes the starting time for the next detection.