Trend data provide important information about the processes in a building automation and control system, e.g.:

  • Monitoring of the control system for optimization purposes
  • Logging the room temperature in association with the set temperature
  • Logging of temperature and humidity trends for the pharmaceutical industry

Offline/Online trend

There are two types of trend data:

  • Offline trend:
  • The recorded trend data are saved in the automation station and uploaded to Desigo CC periodically or as needed. The data can be analyzed in Desigo CC.
  • A connection is needed only during the data upload. Trend objects are needed in the automation station.
  • Offline trend is mostly used for long term data logging.
  • Online trend:
  • Arbitrary data points can be saved as online trends.
  • A permanent connection is needed. No trend objects are needed in the automation station.
  • Online trend is mostly used for temporary data logging.

Trend Log Objects

The trend data is saved in the buffer of the Trend Log and Trend Log Multiple objects in the automation station.

The Trend Log object can only record one value of a data point. The Trend Log Multiple object can record up to six different values of a data point.

The Trend Log object cannot be set up online, but must be set up in advance, offline in the application. A Technical Designation (TD) determines (BACnet reference) which object is to be logged. This presupposes that the referenced object is visible via BACnet (not No Element). The reference and the parameters can be defined and modified online or offline.

When the number of trend log entries reaches a definable threshold (Notification Threshold [NotifThd]), the Trend Log object generates an event. The Trend Log object sends out an alarm which is defined in a notification class specified for Trend Log.

The trend log data acquired can only be read, and if necessary, archived, with a BACnet Client configured for this purpose, e.g., Desigo CC. The status of a Trend Log object is not affected by reading out trend log data. It is not possible to reload sampled data into Xworks Plus (XWP).

A BACnet client cannot reserve a Trend Log object. Every BACnet client can access the Trend Log object. In the case of access or modifications undertaken by several clients, the rule is that the most recent one always takes priority.