User Manual

Alarm management
Alarm sources
9
130 | 353 CM110664en_07
9 Alarm management
Alarms indicate faults in the HVAC plant and building automation and control
system, and let you initiate corrective action, where appropriate. The
management of alarms (generation, signaling, acknowledgement) is in
compliance with the BACnet standard.
There are two alarm types:
● OFFNORMAL
● FAULT
OFFNORMAL alarms (process alarms) occur when a process variable assumes
an inadmissible value. What is inadmissible is determined during engineering.
The relevant parameters are stored in all alarm-generating objects. An
OFFNORMAL alarm always indicates a fault in a plant, while the automation
system itself works properly.
Examples of OFFNORMAL alarms:
● Temperature in HTHW circuit is too high or too low
● Alarm generated by fire detection system
● A damper-motor feedback signal has not been received
● A time schedule cannot execute a command
FAULT alarms are faults in the automation system itself (internal alarms). You
cannot define the cause of a FAULT alarm during engineering. Nor is it possible
for the user to suppress or otherwise influence the monitoring of FAULT
alarms. FAULT alarms are intrinsically linked to the system. A FAULT alarm
always takes precedence over an OFFNORMAL alarm from the same alarm
source, because in the case of a FAULT alarm, there is some uncertainty about
the reliability of the alarm source.
Examples of FAULT alarms:
● Faulty sensor (open circuit, short circuit, etc.)
● Buffer for storage of non-volatile data full
● Access to an I/O module failed
● Bus open circuit (RX integration)
Alarm detection procedure
Every alarm (OFFNORMAL or FAULT) can be uniquely allocated to a source.
The alarm monitoring system is based on the principle of Intrinsic Reporting or
Algorithmic Reporting as defined in the BACnet standard.
Intrinsic reporting means that alarm monitoring (target-actual comparison)
takes place within the alarm-generating object itself (the alarm source). For
this purpose, the function block contains the entire alarm state machine. Alarm
detection does not require any function blocks with external functions. The
alarm behavior of the object is defined by setting variables in the alarm-
generating object (function block).
Algorithmic Reporting means that alarm suppression (target-actual
comparison) occurs outside the alarm source. The alarm state machine is not
located in the function block of the alarm source. For alarm detection, function
blocks with external functions are required. The object's alarm response is not
parameterized using variables of the monitored object (function block).
9.1 Alarm sources
The following function blocks can be alarm sources:
● Analog Input / Analog Output / Analog Value
● Binary Input / Binary Output / Binary Value / Pulse Converter
● Multistate Input / Multistate Output / Multistate Value
OFFNORMAL
FAULT
Intrinsic reporting
Algorithmic reporting