| 摘要 |
PURPOSE:To judge the discrimination between the normal operation and trouble of the titled apparatus, by a method wherein light is incident on a light pervious body from an incident surface thereof to be transmitted therethrough and exited from an exiting surface thereof to be detected by a light receiving element. CONSTITUTION:When a boundary surface 104A to be detected is below an incident point 4, the light 3 from a light emitting element 105 is incident on a light pervious body 1 with an incident angle theta and refracted with an angle r13 of refraction determined by the refractive indices of both substances of a first fluid 101 and the light pervious body 1 and an incident angle theta to reach a light receiving element 2A through a light path 5A in the light pervious body 1. Next, when a boundary surface 104B to be detected is present at a position upwardly exceeding the incident point 4, the light emitted from the light emitting element 105 is incident on the incident point 4 with an incident angle theta and refracted with an angle r23 determined by the refractive indices of both substances of a second fluid 102 and the light pervious body 1 and the incident angle theta, and different from the angle r13 of refraction, to reach a light receiving element 2B through a light path 5B in the light pervious body 1. That is, if a boundary surface 104 to be detected is the boundary surface 104A to be detected in the side below the incident point 4 of light, light is received by the light receiving element 2B. Therefore, when the input of light is not obtained on both of the boundary surfaces 104A, 104B to be detected, it can be judged that this state is caused by the trouble of an apparatus. |
