For this, the component provides two additional communication objects: A “trigger” object,
and an “acknowledge” object.
When the “trigger” communication object receives an alarm value from the bus (the “alarm
condition”), the alarm is activated. This is signalled both visually, in the user interface, and via
the built-in buzzer device. The alarm will remain active until it has been acknowledged by the
user and the trigger object has received the “no alarm” value.
Confirmation (acknowledgement) of the alarm can be done either manually, through the user
interface, or by writing the acknowledge value to the “acknowledge” communication object.
The following flowchart shows the possible alarm states and the transitions between them:
Trigger
"No alarm" value
Acknowledge
Acknowledge
Trigger
OFF
ALARM
WAIT_ACK
WAIT_OFF
"No alarm" value
• Initially all alarms are in the OFF state
• When the alarm condition is triggered, the alarm switches to the ALARM state
• If an alarm is in the ALARM state and the alarm condition deactivates (the “no alarm”
value is received), it switches to the WAIT_ACK state until it is acknowledged.
• If an alarm is in the ALARM state and the user acknowledges it, it switches to the WAIT_OFF
state until the alarm condition deactivates.
• If an alarm is in the WAIT_ACK state and the alarm condition is triggered again, the alarm
switches back to the ALARM state.
2.3
Alarms
25
