Hollis Explorer User Manual - page 45
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Oxygen Sensor Calibration
The EXPLORER is able to perform accurate calibration of the Oxygen (PO
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sensors in ambient air. This has particular importance on the ease and
accuracy of achieving calibrated sensors.
The EXPLORER is able to measure atmospheric pressure during calibra-
tion and make the appropriate calibration adjustments for the sensors.
When performing sensor calibrations, it is important that the calibration gas
and ambient pressure are known.
By using ambient air as the calibration
gas this is known accurately.
The EXPLORER uses advanced empirical techniques to ensure the accura-
cy of the ambient air calibration.
! WARNING: When refitting an oxygen sensor or after calibration of
the sensors, a full Pre-Dive sequence MUST be completed.
The user can cause the largest error in oxygen sensor calibration. If the
calibration is not done in ambient air, the sensors will not give the correct
readings after calibration. Therefore do not execute a manual calibration
without ensuring the sensors are exposed to air at ambient pressure.
The unit's testing for good and bad oxygen sensor calibration is deter-
mined from the sensor mV level detected during calibration. At 1000 mbar
atmospheric pressure the range the unit can calibrate for is approximately
5mV to 15mV. However, if a sensor that would normally show 7.5 mV in air
has an enriched gas (40% Oxygen) applied to it during calibration, then the
sensor will give 14.28 mV. The calibration will pass but the sensor readings
will be dangerously inaccurate.
Calibration Errors
When Oxygen sensors are new or completely dry and a
calibration is undertaken, a small difference will be not-
ed when another calibration is done after a dive. This is
because the humidity inside a unit post-dive affects the
sensor membranes permeability to a small (safe) degree.
In general, it is good practice to calibrate a unit in an
as-dived state i.e. with humidity in the loop. This is per-
formed naturally during the Pre-Dive Check sequence.
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