Visible/IR Lamps for
NDIR Gas Sensors
Gilway offers a line of Visible/IR lamps for use in
applications such as nondispersive infrared gas
sensors, analyzers, and monitors.
Nondispersive Infrared (NDIR) sensors are simple
spectroscopic devices often used for gas analysis.
The key components are an infrared source (lamp),
a sample chamber or light tube, a wavelength filter,
and an infrared detector. The gas is pumped or
diffuses into the sample chamber, and gas
concentration is measured electro-optically by its
absorption of a specific wavelength in the infrared
(IR).
The intensity of IR light that reaches the detector is
inversely related to the concentration of target gas
in the sample chamber. When the concentration in
the chamber is zero, the detector will receive the full
light intensity. As the concentration increases, the
intensity of IR light striking the detector decreases.
Beer鈥檚 Law describes the exact relationship
between IR light intensity and gas concentration:
Beer鈥檚 Law:
I = I
0
e
where:
I = the intensity of light striking the detector
I
0
= the measured intensity of an empty sample
chamber
k = a system dependent constant
P = the concentration of the gas to be measured
NDIR sensors can be used to measure practically
all inorganic and organic gases, but are most often
used for measuring carbon dioxide because no
other sensing method works as simply and reliably
for this gas. Calibration gases of specific
concentration are available for determining the
system constant k for any particular sensor design.
kP
The IR light is directed through the sample chamber
towards the detector. The detector has an optical
filter in front of it that eliminates all light except the
wavelength that the selected gas molecules can
absorb. Other gas molecules do not absorb light at
this wavelength, and do not affect the amount of
light reaching the detector. The IR signal from the
source is usually chopped or modulated so that
thermal background signals can be offset from the
desired signal.
For greater optical efficiency, a reflector assembly
can surround the lamp used for the NDIR sensor.
The reflector is usually parabolic in shape to
collimate the IR light through the sample chamber
towards the detector. The use of a reflector can
increase available light intensity by two to five
times. The reflector surface can also be gold-
coated to further enhance its efficiency in the
infrared.
Applications for NDIR Gas Sensors
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indoor air quality
cycle regulation in self-cleaning ovens
automotive and flue gas emissions
greenhouse farming
hazardous area warning signals
gas leak detection
landfill gas monitoring
alcohol breathalyzers
patient monitoring for anesthesiology
Gilway Technical Lamp
55 Commerce Way
Woburn, MA 01801
Tel: 781-935-4442
Fax: 781-938-5867
www.gilway.com
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