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Detection Principle
●
Catalytic Combustion Type
A catalyst applied to the surface of a platinum coil causes catalytic combustion on the surface of the
catalyst even when the gas concentration level in lower than the lower explosion limit.
The temperature rise in this process increases the electrical resistance of platinum coil. This change
is picked up as deviation voltage for a bridged circuit. You can detect combustible gases up to the
lower explosion limit (LEL).
●
Galvanic Cell Type (Oxygen)
It consists of a noble metal electrode, a base metal electrode, and an electrolytic solution.
A noble metal electrode has contact with the air through the Teflon membrane.
Due to the electrical potential difference from the load resistance caused by connecting to both
terminals, the following reaction takes place:
Noble metal electrode O
2
+ 2H
2
O + 4e
-
→
4OH
-
Base metal electrode 2Pb
→
2Pb2
+
+ 4e
-
As a result, the electrical current commensurate with the oxygen concentration level in the air flows
from the noble metal electrode to the base metal electrode through an external circuit. Because the
electromotive force is temperature-dependent, a thermistor is used to compensate for the variation in
ambient temperature.
11. Detection Principle
