Alarm Communication Flow - GE Mark VIe System Manual

7.6 Alarm Communication Flow

One goal of the alarm system communications infrastructure is to replicate each alarm queue at the point of visualization.
Each Mark VIe controller has an alarm queue and each Alarm Viewer must have a copy of those alarm queue entries in order
to display them. The Alarm Viewers get their information from one or more Alarm Servers, which in turn get queue entries
from the source of the alarms. Each system has at least one Alarm Server. Many systems have a pair of Alarm Server for
redundancy, and these Alarm Servers communicate to synchronize their state machines. The Mark VIe control systems can
support up to a maximum of 10 supervisory PCs with individual alarm server connections to a unit controller (not including
OSM and Historian if present).
A custom TCP/IP based protocol named SDI is used to transfer alarms from the Mark VIe controller to the Alarm Server.
Other custom protocols are used to communicate between the Alarm Server and alarm clients such as the Alarm Viewer. A
change based communication mechanism is used by these protocols, so a client must connect to a server and request an alarm
dump to get the current state of all the alarms maintained by the server. Subsequent changes to that state are communicated to
the client by transition messages. If the connection is lost or if there is any question that the client has the correct state, the
process must be repeated. This is the nature of all change detect protocols, including those used by OPC; the client must first
learn the current state before change of state notifications are useful.
Configuration information about variables, including alarmed variables, is preloaded into the WorkstationST device by using
the ToolboxST application, and is updated automatically by a WorkstatonST service that monitors the controller and uploads
configuration information. This mechanism provides WorkstationST devices and their clients with metadata like variable data
types, descriptions, units, display limits, and all of the other attributes of variables and objects that hold variables. Such
metadata is displayed in the CIMPLICITY and Alarm Viewer screens. Keeping this metadata accurate even as the controllers
and other parts of the system are modified is aided by the unidirectional data flow afforded by having the controllers own the
variables and alarms and their generation. Each HMI can have the same view of the alarm information because each HMI gets
the data and metadata from an alarm server which in turn gets the information from the alarm source, typically the Mark VIe
controller. Synchronization issue with alarm state that can be caused by having multiple alarm sources for the same alarm are
thereby eliminated.
174 GEH-6721_Vol_I_BP GEH-6721_Vol_I Mark VIe and Mark VIeS Control Systems Volume I
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