JPS57147016A - Liquid level sensor - Google Patents

Abstract

PURPOSE:To obtain an inexpensive device with the simple construction work by disposing the terminal parts of a pair of optical fibers having the end faces intersecting diagonally with the axial center by facing each other on the same axial centerline such a way that the end faces assume an open angle. CONSTITUTION:The terminal parts of a pair of optical fibers having the end faces intersecting diagonally with the axial center are disposed by facing each other on the same axial centerline in such a way that the end faces assume an open angle, in a place where the liquid level fluctuates vertically. For example, when the light transmitted through the inside of a core 11 is made incident at the point A on the M-M plane, it refracts and is made incident to the N-N plane at the point B' if the medium around the coupling part is air. Further, it advances by refracting in a core 21, refracts at the point C' on the outside circumference of a clad 22 and advances into the air. If the medium is liquid, it refracts at the point A, is made incident to the N-N plane at the point B, and advances in the core 21, after which it is totally reflected by the boundary face of the core 21 and the clad 22, and further it is reflected totally at the point D and advances in an optical fiber 20. The change in the optical coupling loss between the air and the liquid is measured, whereby the liquid level is known.