Riken Keiki GD-3EC, Technical Manual

Page: 161 / 177

11. Appendix 11-1 Detection principle
161 / 168
11
Appendix
11-1 Detection principle
11-1-1 Non-dispersive infrared absorption type (Infrared type)
<Sensor overview>
This gas detection sensor relies on the fact that many gases absorb infrared radiation. It detects the presence of
a detection target gas by irradiating a measurement cell with infrared and detecting variations caused by target
gas absorption of infrared. It continuously detects all infrared within a specific waveband without dividing
(dispersing) infrared into differing wavelengths.
<Sensor structure and principle>

Structure
A measurement cell and optical filter are positioned between the infrared emitter and the infrared sensor.
Infrared light from the infrared emitter passes through the measurement cell and optical filter before being
detected by the infrared sensor. The optical filter selectively allows the passage of infrared light in the
waveband absorbed by the detection target gas.

Principle
When the detection target gas is introduced into the measurement cell, it absorbs infrared light, reducing the
amount of infrared light detected at the infrared sensor. Based on this principle, a number of samples of
detection target gas of known concentration is introduced to calculate the correlation (calibration curve)
between infrared reduction and the concentration of the detection target gas. The calibration curve can be
used to determine the gas concentration from the measured infrared reduction when an unknown
concentration of detection target gas is introduced.
<Structuree diagram> <Calibration curve (example)>
Detection target gas
concentration
In
frared
re
du
cti
on
Mirror
Detection
target gas Detection
target gas
Infrared emitter
Infrared sensor
Optical filter
Infrared light
Infrared light