Change Of Value (COV) data collection

If connected devices support the SubscribeCOV or SubscribeCOVProperty service, the connector can be configured to use these services to receive notifications every time the Present_Value property of a given object changes by a specified amount called COVIncrement. The SubscribeCOVProperty service allows defining the COVIncrement in the subscription request. The COVIncrement for a SubscribeCOV service is determined by the device. To configure an object for COV data collection, a data selection file must be used. The Data Collection Mode column must be set to SubscribeCOV or SubscribeCOVProperty. If and only if SubscribeCOVProperty is chosen as the Data Collection Mode, the COVIncrement column in the filter file must contain a value greater than or equal to 0 for the given object. A value of 0 means that any change of value will be reported by the device. The Data Collection Interval column must be blank for either type of COV data collection.

If a device disconnects, the connector will re-subscribe upon re-connection for all objects configured for COV data collection. In a scenario where a device shuts down and restarts before a connection timeout occurs, COV subscriptions will be lost until the configured COVLifetime expires at which time the connector will re-subscribe for all objects configured for COV data collection.

When the connector stops, it attempts to unsubscribe from all objects that are successfully subscribed.

Note: If COV data collection is configured for an object, but the device does not support the configured service, then the data selection file will be rejected.