Process Alarms - GE Mark VIe System Manual

7.5 Process Alarms

Process alarms are generated by the transition of Boolean or analog variables configured by the ToolboxST application with
the alarm attribute. The variables are driven by sequencing or tied to input points to map values directly from I/O boards.
Process alarm variables are scanned during each
are voted and the resulting composite is present in each controller.
Process alarms are time stamped and stored in a local queue in the controller. Changes representing alarms are time stamped
and sent to the alarm queue. Reports containing alarm information are assembled and sent over the UDH to the HMIs. Here
the alarms are again queued and prepared for operator display by the alarm viewer.
Operator commands from the HMI, such as alarm Acknowledge, Reset, Lock, and Unlock, are sent back over the UDH to the
alarm queue where they change the status of the appropriate alarm. An alarm entry is removed from the controller queue
when it has returned to normal and has been acknowledged by an operator. The operator or the controller can take action
based on the process alarms setup.
Process alarms can also be created by having the WorkstationST application scan variables and create alarms. This is useful
when alarms need to be created from data coming from third-party equipment.
7.5.1 Process Alarm States and Controller Alarm Queue
Once alarms are generated by the controller (the alarm source), they are placed and maintained in a queue in the controller.
The controller maintains the active alarms with controller state (Active, HI, Low, and so forth) and with the command given
from the operator (acknowledged, silenced, and so forth). The queue structure holds the alarm state, process value, priority,
and shelved, inhibited, silenced, locked, and acknowledged states as well as a timestamp. For a simple Boolean alarm, the
controller alarm state indicates if the process value is beyond alarm limits. Because analog alarms are configured with more
detailed threshold information, analog alarms also have additional information attached to the alarm state relating to those
threshold limits, such as if the process value is below the LO threshold or above the HI threshold.
7.5.2 Process Alarm Development
Process Alarms are typically developed in the Mark VIe controller by using the ToolboxST application. An application
engineer creates Mark VIe application code in Relay Ladder Diagram (RLD) or Function Block language. Alarms are
configured using individual variables in the controller. An Alarm Class, defined at a system level, can be created and
referenced by each alarmed variable to control aspects of the alarm such as priority and color indications. Refer to GEH-6808,
the section How to Configure Alarm Capability in the ToolboxST Application.
Every Boolean variable used in the controller application code has a set of properties including an alarmed property. An
application engineer can set the alarmed property of a Boolean variable so that the variable will cause an alarm anytime its
value transitions to True. For example, if the application code has a Boolean variable called OVERSPD, the user need only
set the Alarm property of OVERSPD to cause an alarm to be generated any time OVERSPD transitions to True.
Analog variables such as integers and floating point REAL values can also be configured for alarming. An application
designer can set High, Low, and other threshold limits of an Analog variable (such as an Integer or REAL) so that an alarm is
generated whenever those thresholds are crossed. This configuration creates child variables in the control logic, and those
variables can be accessed and modified by application code created by the user. For example, if an integer PRES02 variable
exists and the user enables the High threshold limit, a PRES02.H variable is created in application code. The user can write
other application code to change the value of the PRES02.H threshold limit dynamically as the controller is running, and can
use the PRES02.H to drive other control logic. This supports alarm rationalization techniques advocated by ISA 18.2 to
reduce the number of false positive alarms.
172 GEH-6721_Vol_I_BP
frame after the sequencing is run. In TMR systems, process alarm variables
GEH-6721_Vol_I Mark VIe and Mark VIeS Control Systems Volume I
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