Cosmos XP-3110, Инструкция по эксплуатации, Страница: 28 / 32

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Detection Principle
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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).
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Hot-wire Type Semiconductor
When the metal oxide semiconductor heated by the platinum filament adsorbs electron-releasing
gas, such as combustible gas, the electron concentration of the combustible gas will increase and
the specific thermal conductivity of the semiconductor will increase. As a result, the temperature of
the semiconductor will drop and the resistance of the platinum filament will decrease. This resistance
change is output as a voltage deviation change of the bridge circuit. The sensor is very sensitive to
low concentrations, making it suitable for high-sensitivity detection.
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Thermal conductivity type
This type of detector uses the difference in thermal conductivity between a standard gas and the gas
to be detected. When an electrically pre-heated coil of platinum wire is brought into contact with the
gas to be detected, heat is absorbed by the gas or vapor, changing the temperature of the coil. This
change in temperature is almost directly proportional to the concentration of the gas, and produces
a change in the resistance of the platinum coil. This can be measured as a difference in voltage in
terms of the output of a bridge circuit. The relationship between the output and the gas concentration
is virtually
linear, right up to 100%. This makes this type of sensor suitable for measuring high gas
concentrations (0-100vol%).
11. Detection Principle