Limited COV Registrations

The registration for the COV report ("Change Of Value" - event-oriented data transfer) can occur only for the property "Present_Value".

For various older BACnet devices the number of COV registrations is limited. That means that it might happen that the number of unsolicited addresses is bigger than the number of the available COV registrations in a device.

A limitation of the COV entries occurs only when using an older device model. In such a case the following approach is taken:

  1. All addresses, where the registration failed, are counted and written on the corresponding internal device data point element.

  2. An error message is also written into the WinCC OA log file, which informs about the address of the failed registration.

  3. If this address could not be registered for COV, it must be configured for polling partly manually.

When designing the system, it is to consider that the number of COVs does not exceed 200 COVs per second due to the danger of getting a buffer overflow.