Manual Version 19 / 01-2019 II Page 16 of 44
SF2 ECCR OPERATION MANUAL
In order to be able to compensate for various pressure fluctuations, a compensating
membrane is built into most sensors on the back. This is also necessary to cushion
volume fluctuations due to temperature changes. But that means that the
compensating membrane is always the same Pressure must be exposed like the
sensor membrane. If a sensor is installed in such a way that the compensation
membrane is not exposed to the ambient pressure, this not only leads to incorrect
measured values but also to the destruction of the sensor.
Oxygen sensors behave like a human body underwater. Since the main component
of the sensors is a liquid, they absorb gas when descending and release it again
when ascending.
To do this, they need time to stabilize. Rapid changes in pressure or temperature
can therefore lead to a "DCS" and influence the function of the sensor. Above all,
reducing the pressure too quickly can lead to the formation of bubbles in the
electrolyte. Bubbles in the sensor prevent the diffusion of the
Oxygen. The oxygen measurement stops and the output drops.
3.3 Influence of moisture and water
Moisture does not directly affect the accuracy of a good sensor. However, the
moisture in the gas takes up a certain proportion of the volume and thus also exerts
a partial pressure. The partial pressures of the remaining gas components are
reduced accordingly and the sensor shows less oxygen
increasing humidity (in the same environment).
However, extreme humidity or even condensation on the sensor surface significantly
impair the sensor function. Water on the sensor membrane prevents the diffusion of
oxygen so that the sensor becomes inoperable. In environments with extremely high
humidity, the membrane should be used before
Calibration or measurement can either be carefully wiped off with a soft, lint-free
cloth and / or the sensor held down during the measurement. This can cause drops
to form due to the surface tension of the water, which fall downwards. Also the slight
(!) Flow of dry gas from a diving cylinder across the Membrane can lead to drying of
the moisture.
Rebreather systems in particular have the problem of high gas humidity (due to
breathing) and condensation (due to the cold surrounding water). To prevent
malfunction of the sensors due to condensation, they are usually built into the head
in a special way. During calibration, the humidity would have an influence on the
result. But since you (at least When rebreather diving) calibrated with dry diving
gases, this problem is usually eliminated. However, due to the high humidity in the
circuit, calibration should never be carried out after a dive.
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