Crowcon Tetra MO7237, User Manual, Page: 18 / 36

Alarm indications Tetra
IV. Alarm indications
Tetra provides two instantaneous alarm levels for each installed sensor, des-
ignated level 1 and level 2. For toxic gas sensors, there are also two time
weighted average alarms (TWA), one for short term exposure (STEL): based on
a 15 minute time weighted average, and the second TWA alarm is for long term
exposure: based on a 8 hour time weighted average.
Alarm configurations are set via the Crowcon Portables PC software.
The following settings can be made:
Alarm thresholds for each sensor
: Level 1
and level 2 alarms can be set for each individual
gas sensor.
Alarm type: This can be set to rising levels of gas concen-
tration, or as falling. Oxygen sensors are set to falling for
deficiency monitoring.
Alarm latching: Alarms can be set to be latched or
unlatched. Latched alarms will require the operator button to
be pushed in order to clear the alarm. This is the default set-
ting. Unlatched alarms will clear automatically when the gas
hazard has passed.
Alarm mute:
The sounder can be set to mute for level 1
alarm only; pressing the operator button during an alarm
condition ie presence of hazardous gas, will silence the
sounder and stop the vibration alarm. The alarm LEDs will
continue to flash.
Alarm sounder tone:
Different tones can be selected to
achieve the best performance for the monitoring conditions
available.
In the event of a Time Weighted Alarm (TWA)
In the event the 15 minute or the 8 hour TWA is triggered,
Tetra will go into alarm and display the TWA icon with the
toxic gas readings. The 8 hour TWA alarm cannot be cleared.
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