MEASURING INSTRUMENT FOR CONTAMINATION DEGREE OF OIL

PURPOSE:To eliminate the effect of a disturbance and to improve the measurement efficiency of the instrument by separately receiving a direct light component and a scattered light component and measuring the logarithmic ratio of both components. CONSTITUTION:Oil 11 to be measured is irradiated by a laser beam 10 from a laser light source 9, and most of the laser beam 10 is passed through a condensing lens 12 as direct light 13 and condensed on the first light receiving surface 15a of a photodetector 15. When the oil 11 contains contaminants, scattered light 14 is emitted and condensed on the second annular light receiving surface 15b of the photodetector 15. The photoelectric currents generated on the light receiving surfaces 15a and 15b are converted into voltage signals V1 and V2 by photoelectric current/voltage convertors 16 and 17. Accordingly, the logarithmic ratio of the signals V1 and V2 is calculated by a logarithmic amplifier 18, and the output is subjected to A/D conversion 19 and digitally indicated on an indicator 20 as the contamination degree.