HAFFMANS c-DGM/i-DGM
Page 16 of 78 c-DGM/i-DGM
4.2 Measurement principle
*O
2
measurement
O
2
measurement is based on measuring the luminescence of an oxygen-sensitive layer. The
fluorescence changes depending on the partial oxygen pressure. The quantity of dissolved gas
in the liquid is calculated by using the partial oxygen pressure and temperature.
CO
2
measurement
The measurement of CO
2
is based on Henry's law, which describes the equilibrium between a
gas and a liquid in an enclosed space. The law says that, at a constant temperature, the
quantity of gas dissolved in the liquid is proportional to the partial pressure of the gas above the
liquid.
It is therefore possible to measure the quantity of CO
2
dissolved in a liquid sample by measuring
both the equilibrium pressure of CO
2
above the liquid and the temperature of the liquid. The
concentration is calculated with the CO
2
formula (see Appendix I).
4.3 CO
2
measurement
The handle (pos. 20) operates the lever (pos. 07), which automatically regulates the inlet, the
outlet, and the connection from the expansion vessel to the measurement chamber.
The handle has two positions:
Sampling: The handle is retracted.
The inlet and outlet of the instrument are open and the expansion vessel
is connected to the outlet.
Measurement: The handle is depressed.
The inlet and outlet of the instrument are closed and the expansion
vessel, which functions as a gas reservoir, is connected to the
measurement chamber. Depressing the handle initiates the
measurement.
The throttle valve is located in the outlet of the measurement chamber and regulates the flow of
the product through the measurement chamber.
The measurement results (temperature, pressure, and CO
2
value) are displayed and stored in
the logbook.
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