O 2 Measurement - Pentair HAFFMANS c-DGM Instruction Manual

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4.4 *O measurement
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The oxygen sensor (pos. 23) is located behind the inlet (pos. 17) of the DGM and in front of the
inlet to the CO measurement chamber (pos. 02).
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There are two different types of oxygen sensor available for the c-DGM. The LHO sensor is
suitable for measuring very accurately at low oxygen concentrations, the WLO sensor is
suitable for measuring for higher oxygen concentration over a wider measuring range.
The oxygen sensor measures the O content of the liquid optically by using the luminescence
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measuring principle, where an oxygen-sensitive layer is illuminated with blue light. This causes
molecules in the oxygen-sensitive layer to enter an excited state.
Fig. 4.3 Luminescence when oxygen is not present
When not in the presence of oxygen, the molecules emit red light. When there is oxygen
present, the gas collides with the molecules in the oxygen-sensitive layer. The molecules that
collide with oxygen do not emit light. Through this process there is a link between the oxygen
concentration and both the light intensity and the speed of reduction of the light intensity. The
light intensity increases at higher oxygen concentrations whereby the speed of the intensity
reduction increases.
The oxygen concentration is calculated from the product temperature and the elapsed time
between exposure and illumination (phase shifting).
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