PHOTOELECTRIC TYPE LIQUID SURFACE DETECTION UTILIZING TOTAL REFLECTION OF LIGHT

摘要

PURPOSE:To minimize the effect of interference by a method wherein the reflecting surface of a prism having incident, reflecting and emitting surfaces is made a liquid detecting surface, light irrdiates the reflecting surface from the incident surface and then, allowed to the transmitted therethrough or reflected therefrom utilizing changes in the critical angle of light depending on the difference in the diffractive index to enable the detection of a transparent liquid. CONSTITUTION:The surface 5 of a prism 4 having an incident surface 8, a reflecting surface 5 and an emitting surface 11 is made a detecting surface and set horizontal at the height of the liquid surface 6 with the apex angle 7 thereof within the liquid area 3 so that the reflected light 10 of an incident light 9 from a projector 1 on the surface 5 can be received with a receiver 2. Then, the incident angle of the light 9 to the surface 5 set above the critical angle of light of the prism 4 with respect to gas and below the critical angle of the prism 4 with respect to liquid. When gas exists on the surface 5, the light 9 is totally reflected to be incident into the receiver 2 while it is transmitted mostly therethrough when liquid exists.