COSA Xentaur COSA 707 - Manual (Page 11)

COSA Instruments USER MANUAL COSA 707
The advantage of this technology is that the signal generated is direct proportionally and
linear to the volume concentration (% or ppm) of the analysis gas components.
The 3 electrodes are: S (sensing electrode), C (counter electrode) and R (reference elec-
trode).
When the gas being measured contacts the sensing electrode, it reacts on the electrode surface
either through oxidation (for example CO, SO
2
, NO) or reduction (like NO
2
, and Cl
2
).
Example: CO sensor:
CO reacts at the sensing electrode as follows:
CO + H
2
O -> CO
2
+ 2H+ + 2e-
and at the counter electrode, oxygen from air will be re-oxidized to water:
½ O
2
+ 2H+ + 2e- -> H
2
O
The sensor supplies a constant current signal (µA-range) that is monitored and analyzed. The cur-
rent intensity is dependant upon the volume concentration of the sample gas, while other parame-
ters like temperature and cross sensitivity are calculated by the analyzer.
Pos.
1 Sample gas
2 Particle filter
3 Sensing Electrode
4 Reference Electrode
5 Counter Electrode
6 Connection pin
7 Electrolyte reservoir
8 Electrolyte
9 Capillary diffusion barrier