COSA Xentaur COSA 707 User 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