COSA Xentaur SF6 Purity Pro - Manual (Page 22)

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10. MEASURING PRINCIPLE
The Reflection ratio of gas mixture is determined by the kinds of composing gases as well as the
mixture ratio. As long as the kinds of composing gases are known, the mixture ratio (concentration)
can be determined by measuring the reflection ratio.
The optic interferometer applied in the RK60000 displays “Interference Stripes” on the CCD. The
Interference Stripes move proportional to the reflection ratio. The amount of the movement is
measured by the solution of the interference stripes on CCD with Fourier analysis, and the result is
converted to the reflection ratio.
Concentration can be displayed by adding data like “measuring gas” and “base gas” to the
reflection ratio determined by high accuracy. Sensitivity of the optic interferometer depends on the
length of the chamber. Since the length of the chamber is physically unchanged by elapsing time,
the high accuracy is maintained for awhile.