Oxymax W COS71
2
Hauser
Function and system design
Measuring principle
The oxygen molecules diffused through the membrane are reduced to hydroxide ions (OH-) at the cathode.
Silver is oxidized to silver ions (Ag+) at the anode (this forms a silver halogenide layer).
A current flows due to the electron donation at the cathode and the electron acceptance at the anode. Under
constant conditions, this flow is proportional to the oxygen content of the medium.
This current is converted in the transmitter and indicated on the display as an oxygen concentration in mg/l,
as a saturation index in % SAT or as an oxygen partial pressure in hPa.
Potentiostatic amperometric
three-electrode system
The high-impedance, current-free reference electrode plays an important role.
The formation of a silver bromide or silver chloride coating on the anode uses up the bromide or chloride ions
dissolved in the electrolyte
In the case of conventional membrane-covered sensors working with the two-electrode system, this causes an
increase in signal drift.
This is not the case with the three-electrode system:
The change in bromide or chloride concentration is registered by the reference electrode and an internal control
circuit holds the working electrode potential constant. The advantages of this principle are significantly
increased accuracy of the signal and considerably extended calibration intervals.
Measuring system
A complete measuring system comprises at least:
• Oxygen sensor
• Transmitter, e.g. Liquisys M COM223/253-WX/WS
• Special measuring cable
• Assembly, e.g. flow assembly COA260 or retractable assembly COA451
Optional:
• Junction box VS (with cable extension)
a0004102
Measuring system (example)
1
Flow assembly
2
Junction box VS (optional)
3
Transmitter Liquisys M COM253
4
Oxygen sensor
