22
８－３.
Detection principle
The refractive index of gas mixture is determined by the kinds of composing gases
and its mixing ratio.
As long as the kinds of composing gases are known, the mixing ratio(concentration)
can be determined by measuring the refractive index.
The optical interferometric sensor applied in the FI-800 displays “Interference
fringes” on the image sensor.
The interference fringes which shifts in proportion to refractive index is reflected
onto the image sensor.
The image of interference fringes is photographed by image sensor and the amount
of the movement is measured with Fourier analysis technique. And the result is
converted to the refractive index.
Concentration of several gas mixture can be displayed by adding some data like
“measuring gas” and “base gas” to refractive index determined accurately.
Sensitivity of the optical interferometric sensor depends on the length of the
chamber. Since the length of the chamber is physically unchanged by elapsing the
time, the high accuracy is maintained for a long time.
Chamber
Plane parallel
mirror
Prism
Mirror
LED light source
Image sensor
Lenses
Optical Interferometric Sensor
