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Maintenance mode 1 and 2 is available with the base unit without a main unit.
The base unit can produce a 4.0mA or 17.4mA analog output while in
maintenance mode 2. This function is useful for loop check at startup, etc.
*3. It is possible to set/cancel the maintenance mode (
“host maintenance mode”)
from the host system/device via the base unit using Modbus communication.
The operation of the host maintenance mode is the same as maintenance
mode 1.
NOTE
While in maintenance mode, the status information of gas/trouble alarms is sent to the
host system (e.g. control room) digitally. If the gas alarm contacts/trouble alarm open
collector are used to operate the interlocks of the external devices, release the
interlocks beforehand, as needed to prevent a possible activation of the interlocks
during the maintenance mode.
When switching the maintenance switch from MNT1 to MNT2 or vise versa, the gas
detector briefly enters the normal operation mode. If switching is done while an alarm
condition exists, an alarm signal will be output. If the alarm contacts/open collector
are used to operate the interlocks of the external devices, release the interlocks
beforehand, as needed to prevent a possible activation of the interlocks during
switching the maintenance switch.
*1. Trouble alarm will activate if the main unit power switch is set to the OFF position during
MNT1 or MNT2 mode. (OFF)
*2. The analog output may change when the main unit power switch is set to the OFF position.