Siemens Rapidlab 1200 - Page 59

Rapidlab 1200 Operator’s Guide: System Overview and Intended Use 1-39
02087462 Rev. V
pO
2
Sensor
The pO
2
sensor is based upon the electrode described by Clark.
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It is a complete
electrochemical cell that incorporates amperometric technology. The sensor
consists of a platinum (Pt) cathode, and silver (Ag) anode, an electrolyte solution,
and a gas-permeable membrane.
Figure 1-32 pO
2
Sensor
A constant voltage, called a polarizing voltage, is maintained between the anode
and the cathode. As dissolved oxygen from the sample passes through the
membrane into the electrolyte solution, it is reduced at the cathode:
−−
→++ OHeOHO 442
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The circuit is completed at the anode, when the Ag is oxidized:
−+
+→ eAgAg 44
The amount of reduced oxygen is directly proportional to the number of electrons
gained at the cathode. Therefore, by measuring the change in current (electron
flow) between the anode and the cathode, the amount of oxygen in the electrolyte
solution is determined.
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1 Cathode contact
2 Anode contact
3 Sample path