10 Product Specifications
10-2. Principle of this product
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10-2-3. Principle of optical sensor
A schematic diagram of the interferometer used in the optical sensor is shown above. This
interferometer forms "interference fringes" that move in proportion to the "differences of refractive
index" between the measuring and reference gases.
The movement distance of interference fringes
Δ
θ
can be expressed as the following formula:
REF
GAS
n
n
L
2
L
: Chamber length
n
GAS
:
Refractive index of measuring gas
n
REF
: Refractive index of reference gas
λ
: Light
source
wavelength
The light source wavelength and chamber length are physically quite stable. Therefore, the refractive index
of measuring gas
n
GAS
can be accurately obtained by measuring the movement distance of interference
fringes.
GAS chamber
Plane-parallel mirror
Prism
Mirror
LED light source
Lens
Lens
Interference
fringes
Reference gas
Measuring gas
a
b
L/2
Measuring gas
Interference fringes such
as the ones shown above
are formed here.
c
