The measured value is displayed directly as %O₂ to a resolution of 0.1 %O₂, with a measuring range of 5 to 100 %O₂.

The Oxygen Level Monitor differs from other types of ALARMLOG, in the generation of out of limit alarms, in two significant ways:

1. Sensor Alarm Levels

   Instead of high and low sensor alarm levels, the oxygen monitor has two low alarm levels, each independently settable to a resolution of 0.1 %O₂.

   The upper is intended as a warning alarm and is designed to give advance warning of a reduction in oxygen levels. The lower is intended as a critical alarm and is intended to advise of unsafe conditions within the monitored enclosure.

   Provided that measured oxygen levels have recovered to normal, a warning alarm will be cancelled automatically after a period of five minutes, or multiple thereof, without operator intervention. A warning alarm may also be cancelled at any time by the operator. An optional alarm delay of between 1 and 99 minutes may be specified by the user before a warning alarm is generated.

   A critical alarm will occur as soon as the relevant alarm conditions have been present continuously for a period of approximately 15 seconds. A critical alarm can not be delayed further. A critical alarm must be cancelled by operator intervention.

2. ALARMLOG External Alarm Outputs

   The oxygen monitor is provided with two external alarm outputs in place of the single output provided on other versions.

   One output is energised whenever a warning alarm is present. This might be used, for example, to control ventilation fans.

   The other output is energised whenever a critical alarm is present. This might be used, for example, to energise an external visual and/or audible alarm.

   Both external alarm outputs are at low voltage signal levels and must be used in conjunction with a special interface relay unit which is separate from the ALARMLOG.