Specifications

Halogen Gas Monitor – MultiZone Remote Display
Instruction 3015-5157 56
Notes on Alarms and Alarm Acknowledge
The HGM-MZ can be operated in two different alarm acknowledge modes, Auto and Manual (set via the
alarm_ack_mode variable in the system data register). For purposes of this discussion, the term “Alarm”
refers to a HGM-MZ state where the alarm light is on and the appropriate alarm relay is activated. The term
“Alarm condition” refers to the external condition (i.e., refrigerant leak) that initially causes the HGM-MZ to go
into an alarm. If an alarm occurs it can be handled in one of 3 ways.
1. Non-Latching Mode. This mode is enabled by setting the AUTO_ACK_MODE parameter in the
system register to “1”. In this mode, if an alarm condition occurs an HGM-MZ alarm will be created. If
the alarm condition is subsequently removed, the HGM-MZ alarm will automatically be cleared by the
HGM-MZ when the zone in alarm is sampled “clear”. Note, in this mode of operation, it is possible for
an alarm to occur and be cleared without user or MODBUS master intervention. If this is the case, the
only evidence of the alarm would be contained in the HGM-MZ alarm log.
2. Latching Mode with Silence. This mode is enabled by setting the AUTO_ACK_MODE in the system
register to “0”. In this mode, if an alarm condition occurs, an HGM-MZ alarm will be created. In order
for the alarm to be removed the MODBUS master will write a “0” to the ALARM parameter in the ZONE
register. This will cause the alarm to be “silenced” in the HGM-MZ (i.e., the alarm relays will return to
their normal state and the ALARM lamp will be extinguished). The next time the zone with the alarm
condition is sampled, if the alarm condition still exists, the alarm will be reactivated and the alarm
parameter will be reset to “1” in the HGM-MZ. Otherwise, if the alarm condition has cleared, no further
action is required and normal operation will resume.
3. Latching Mode without Silence. This mode is enabled by setting the AUTO_ACK_MODE in the
system register to “0”. In this mode, if an alarm condition occurs, an HGM-MZ alarm will be created.
The HGM-MZ MODBUS master will then write a “1” to the ALARM ACK parameter in the zone
register. The alarm will continue to persists (i.e., Relays in alarm state and Alarm light on) until the
offending zone is sampled and no alarm condition is detected. At that point, the ALARM ACK
parameter is automatically cleared by the HGM-MZ, as is the ALARM parameter. NOTE: If the
ALARM ACK parameter is set to “1” and the ALARM CONDITION is upgraded (from leak to spill, or
spill to evacuate) the ALARM ACK parameter will automatically be cleared to “0” by the HGM-MZ.