| 摘要 |
PURPOSE:To prevent deterioration in concentration detecting sensitivity due to immersion for a long period, by forming a protecting layer, which has a refractive index satisfying special conditions, on the surface of a photoconductive medium. CONSTITUTION:A light emitting element 2 and a photodetector 4 are linked with a photoconductive medium 3 in contact with a liquid to be measured 5. A light emitting wavelength is set at a value in a wavelength band to which the liquid 5 has light absorbing sensitivity. The state of the liquid is detected at the output level of the photodetector 4. At this time, a protecting layer 9, which has a refractive index satisfying the condition of n1<n2>=n3, is formed on the surface of the medium. In the expression, n1 is the refractive index of the liquid 5, n2 is the refractive index of the protecting layer 9 and n3 is the refractive index of the medium 3. The protecting layer 9 is formed with a bridging structure of polyene, polyorganosiloxane, or the medium 3. Thus, deterioration in concentration detecting sensitivity due to immersion for a long period is prevented. |
