Abstract: An optical liquid level sensor has an optically-transmissive body (28) provided with a frusto-conical tip end portion (32). When the tip end portion is exposed to air, the angle of incidence (.theta..sub.i) of light at each of three points of reflection (b,c,d) is less than the critical angle (.theta..sub.c) such that substantially all light transmitted through the body will be reflected internally. However, when the tip end portion is exposed to a liquid, light is refracted, and the intensity of the reflected light is reduced. The intensity of the reflected light is used to indicate whether the sensor is above or below the surface of the liquid.

Abstract: An optical apparatus for measuring physical quantities, comprising an optical transducer (33) for sensing position, outgoing and return optical fibers (20,23), and an electronic control module (43). Light is generated at the control module and is transmitted by the outgoing optical fiber (20) to the optical transducer (33), which simultaneously varies the relative intensities of two different colors in a dissimilar manner in response to location of a positionable device (34,35) in the optical transducer. The modified intensity is transmitted back to the control module via the return optical fiber (23). The control module (43) measures the intensities of the two returning colors, and then outputs an electrical signal proportional to the intensity ratio for analog applications, or, alternatively, tests the intensity ratio against preselected constants and outputs discrete signals for digital application.

Abstract: A temperature measuring device comprises an optical temperature probe (20) and a control module (21). Thermal emission from a recess (28a, 28b) in the tip end portion (23) of an optical fiber (22) is transmitted to the remote end (26) of the fiber for detection by the control module. The recess provides improved sensor capability with regard to maintaining constant emissivity and rapid response time. The recess is suitable for both single crystal optical fiber and optical fiber with a core-and-cladding construction.