Hollis Explorer User Manual - page 52
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change its characteristics post-dive. Therefore, as previously stated, the
filter should always be changed within 24 hours of opening and/or use.
Partially used filters should be stored in the EXPLORER with a closed
breathing loop.
Although the algorithm that analyzes the thermistor curve is adequately
accurate during diving, if the filter is not being breathed on, the thermistors
curve will be abnormal. It also takes time for the absorbent to rise to nor-
mal operating temperatures. Therefore for routine use, the addition of the
Oxygen injection meter (described in the next section) is used to report the
filter percentage remaining to the user.
OXYGEN INJECTION METER
The CO
2
created by the diver is in direct proportion to the oxygen
breathed. The oxygen metabolized by the body is replaced by the in-
jection of oxygen into the breathing loop. By knowing the volume of gas
injected, the amount of metabolized oxygen and therefore the amount
of CO
2
created can be estimated. From tests, the duration of the filter
types has been determined and the corresponding volume of CO
2
ab-
sorbed before the absorbent begins to reduce its effectiveness.
Using these principles, the system measures the amount of gas injected
by the solenoid valve and converts it to a percentage of minutes remaining
at CE CO
2
rates. Although the displayed minutes are at CE CO
2
generation
standards, the minutes will tick down more slowly if the diver is breathing
at a reduced rate. This will be the most common scenario. However, in the
unusual condition of CO
2
generation at an elevated rate compared to 1.6ltr/
min then the minutes will tick off more quickly. If the diver knows a particu-
larly strenuous dive is ahead, they should allow extra conservatism in the
minutes remaining counter, for that dive.
The Oxygen Injection Meter should be used in conjunction with the Tem-
perature profiler and the Gaseous CO
2
sensor to determine the appropriate
state of the filter. The remaining Oxygen injection meter percent is dis-
played on the STATUS screen as a ‘Filter minutes’. The Oxygen Injection
Meter minutes are reset when the absorbent is replaced and confirmed in
the Pre-Dive Sequence.