User Manual

Alarm management
Alarm example
9
132 | 353 CM110664en_07
With analog blocks, the OFFNORMAL state is explicitly subdivided into the sub-
states HIGH LIMIT and LOW LIMIT, which are described in detail further below.
The current state of the alarm state machine in an alarm-generating block is
displayed externally in the form of the output variable [EvtSta] (event state) of
the block concerned.
State transitions between alarm states
Transition Trigger Action / Event state
TO_OFFNORMAL A new OFFNORMAL alarm condition has been detected. OFFNORMAL
TO_NORMAL1 The current OFFNORMAL alarm condition has disappeared, and there
is no other alarm condition present.
NORMAL
TO_FAULT A new FAULT alarm condition has been detected. FAULT
TO_NORMAL2 The current FAULT alarm condition has disappeared, and there is
currently no other alarm condition.
NORMAL
System events may also occur within each alarm state. These message
functions do not affect the alarm state.
Because FAULT alarms take priority over OFFNORMAL alarms, the state
transition from FAULT to OFFNORMAL only occurs under very special
circumstances.
If, while in the OFFNORMAL state, a FAULT alarm condition occurs, there is
then a state transition TO_FAULT (because as stated above, FAULT takes
priority over OFFNORMAL).
9.2 Alarm example
The following figure shows the main information exchanged by the elements
concerned, namely:
● Operator
● Ventilation system sensor/actuator (differential pressure monitor,
maintenance switch and single-speed extract air fan)
● PXC program
● Desigo CC plant graphic
● PXM… operator unit
What happens in the
Desigo system when
the V-belt of an
extractor fan breaks?