User Manual

Global objects and functions
Ensuring data consistency
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7 Global objects and functions
Every automation station contains all the data necessary for stand-alone operation, including, e.g., date and
time, calendar function blocks and Notification Class function blocks. The system functions of individual
automation stations do not depend on a central server.
The System View and the Program View are based on the automation station, that is, each object (block,
BACnet data object) belongs to a specific automation station. These objects are called local objects. This
form of representation is adequate for most elements of a physical plant, e.g., for the supply air
temperature or the set point of a ventilation system.
However, certain data objects need to be visible in identical form in some or all the automation stations of
a site. These objects are called global objects. Global objects let you centrally change parameters, which
are then distributed to all automation stations.
Local objects
Local objects are individual and unique objects which exist only once on a particular automation station in
the system. Most application-related objects are local objects. When local objects are required, such as the
outside temperature in several automation stations, access to this data must be configured or programmed
explicitly with function blocks (such as analog, binary and multistate inputs, or grouping in the room
management system) and referencing.
Global objects
Global objects are data objects which exist simultaneously on each automation station at the automation
level. Global objects are always global within a given site. Global objects are engineered in Xworks Plus
(XWP).
Global objects are compiled in a global chart. There is exactly one global chart per site. You can modify
global charts, save them in the tool's library folder, and copy them to other projects.
7.1 Ensuring data consistency
Primary copy
The primary copy procedure ensures that the global objects are consistent at all times. This means that all
copies of a particular global object contain the same value and any modification of a value is transmitted to
all copies.
Primary and backup server
Only one automation station per site acts as the primary server for all global objects of this site. All other
automation stations of this site are backup servers. A client may only modify the values of the global
objects on the primary server. The primary server then updates the copies of the modified global objects on
all backup servers. A backup server accepts the modifications to global objects only from its primary server
but not from a client.