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10. Detection principle
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NDIR method (Non-Dispersive Infrared)
Model RX-415 is based on NDIR method (Non-Dispersive Infrared) and this structure is shown
below.
The infrared beam emitted from the light source passes through the measuring cell, and optical
band pass filter which can pass the absorption wave of measuring gas and attains to the infrared
sensor. The amount of infrared attaining to the infrared sensor through the measuring cell and will
decrease according to its density.
The variable amount of infrared is measured by the infrared sensor and it is displayed as gas
concentration.
Then, there is no sensitivity against CO2 and CO etc which have the different absorption wave
from the measuring gas. Then there is no sensitivity against N2 and H2 etc which cannot absorb
infrared. As compared with the conventional catalytic combustion method, there is no poisoning
material to be absorbed and almost no sensitivity drop on this detection principle.
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GALVANIC CELL method
Galvanic cell consists of a lead anode and a gold cathode in electrolyte covered by a membrane.
When oxygen enters into the gold cathode, a current which is directly proportional to the oxygen
concentration will be produced, and amplified current will produce a reading on a meter in percent
oxygen.
Light source
Measuring cell
Amp.
Band-pass Infrared
filter sensor
Measuring gas
Membrane
Gold electrode
(Cathode)
Lead wire
Solution
Lead electrode
(Anode)
Thermistor
Out put
