User Manual

Global objects and functions
Ensuring data consistency
7
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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 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 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
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.
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.
Local objects
Global objects
Primary copy
Primary and backup
server