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12.
Detection Principle
Detection principle
The refractive index of gases is determined by the types of composing gases and the mix ratio. When a
mixed gas consists of two different gases and the types are known, the mix ratio (concentration) can be
obtained by measuring the refractive index.
The optical interferometric sensor used for the purity meter forms an "interference fringe" that moves in
proportion to changes in refractive index on the image sensor. Then the interference fringe is captured by
the image sensor and converted into a refractive index after calculating the move amount of interference
fringe with a high degree of accuracy through the phase analysis processing.
The "concentration" display of various mixed gases is enabled by inputting the data such as type and
refractive index of "measuring gas" and "base gas" that compose a mixed gas to the "refractive index"
calculated with high accuracy.
The sensitivity of optical interferometric sensor depends on the length of the chamber that flows gases.
Because the chamber length is physically unchangeable, high accuracy is maintained over a long period of
time.
Schematic View of Optical Interferometric Sensor
Chamber
Plane parallel mirror
Prism
Half mirror
LED light source
Image sensor
Lens
LED light source
Mirror
