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MEASURING PRINCIPLE
2 - 8
ETC00781(1) Series 100 e 10/2001
OXYGEN MEASUREMENT (EO
2
ELECTROCHEMICAL PRINCIPLE)
2.2.2 Electrochemical Measurement
The determination of O
2
concentrations is based on the principle of a galvanic cell.
The principle structure of the oxygen sensor is shown in Fig. 2-5.
Fig. 2-5: Structure of electrochemical Oxygen Sensor
The oxygen senor incorporate a lead/gold oxygen cell with a lead anode (1) and a gold cathode
(2), using a specific acid electrolyte. To avoide moisture losses at the gold electrode a sponge sheet
is inserted on the purged side.
Oxygen molecules diffuse through a non-porous Teflon membrane (4) into the electrochemical cell
and are reduced at the gold-cathode. Water results from this reaction.
On the anode lead oxide is formed which is transferred into the electrolyte. The lead anode is
regenerated continuously and the electrode potential therefore remains unchanged for a long
time.
The rate of diffusion and so the response time (t
90
) of the sensor is dependent on the thickness
of the Teflon membrane.
Lead wire (Anode)
Lead wire (Cathode)
Anode
(1)
(Lead)
O - ring (8)
Plastic disc (9)
Plastic top (10)
Resistor (6)
Thermistor (5)
Acid electrolyte (3)
Sponge disc (7)
Teflon membrane (4)
Cathode
(2)
(Gold film)
(Black)
(Red)