Patent ID: 7759651

Claim:
A process for measuring transmittance of a fluid in a radiation field comprising radiation at a first wavelength and radiation at a second wavelength different from the first wavelength, the process comprising the steps of: (i) positioning a polychromatic radiation source and a polychromatic radiation sensor element in a spaced relationship to define a first thickness of fluid in the radiation field; (ii) detecting a first radiation intensity corresponding to radiation at the first wavelength received by the sensor element at the first thickness; (iii) detecting a second radiation intensity corresponding to radiation at the second wavelength received by the sensor element at the first thickness; (iv) altering the first thickness to define a second thickness; (v) detecting a third radiation intensity corresponding to radiation at the first wavelength received by the sensor element at the second thickness; (vi) detecting a fourth radiation intensity corresponding to radiation at the second wavelength received by the sensor element at the second thickness; and (vii) calculating radiation transmittance of the fluid in the radiation field from the first radiation intensity, the second radiation intensity, the third radiation intensity and the fourth radiation intensity.