be adjusted from the instrument keypad (see
Section 8) by means of a screwdriver. Alarm
thresholds may also be set via the computer
interface (see Section 12) and the following
parameters may be set for instantaneous alarms:
•
Normally triggered on a rising level, alarms
may be set to trigger on a falling level as with
oxygen deficiency alarms.
•
Alarms may be latching, requiring manual
reset, or self clearing when the hazard has
passed.
•
Normal alarms cannot be cleared whilst the
gas hazard persists. It is possible to set level
1 so it may be silenced (the red LEDs will
continue to flash). This allows the user to set
a ‘pre-alarm’ warning at a low gas level and a
non-silenceable alarm at a higher level.
•
Unused alarms may be deactivated.
•
The level 1 alarm may be set to be visual only
(not oxygen units).
If any alarm event is triggered, the red LEDs will
flash and the sounder will emit a loud tone. Each
alarm type has a different tone sequence which
can be selected from a menu if using
SetPortable
software (Section 12). Alarm 2’s tone
takes precedence over alarm 1’s tone. The alarm
type will be indicated by a flashing symbol on the
LCD (see Section 5.2). If either of the TWA (time
weighted average) symbols appear on the
display, this indicates that the cumulative
exposure to toxic gas has been reached for an
8-hour shift or a 15 minute ‘window’. UK Health
& Safety regulations require that workers should
leave the hazardous area once they have
exceeded this dose. A TWA alarm cannot be
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