Optical-electrical liquid probes

Claim 1

An optical-electrical liquid probe comprising a light emitter, a light receiver in the form of a photo-electric transducer, a body which is translucent to light rays and having at least one surface which can be exposed to a liquid, said light emitter being arranged to emit light rays, so that they strike, from within the body, the said surface which can be exposed to liquid, and are refracted, in the absence of liquid at the said surface, in the direction of the light receiver, wherein said translucent body is in the form of a hollow body defining an internal space, and said body comprises a widened hollow upper part, a narrowed hollow part having a circumferential wall, and a shoulder part located between the said parts, the narrowed lower part has a closed end remote from the shoulder part and is arranged to be externally exposed to liquid, the light emitter is located in the said internal space of the hollow body such that the light rays emitted by the light emitter pass outwards through the outer surface of the circumferential wall of the narrowed lower part at an acute angle and in such predetermined directions that, in the case of the absence of liquid from the vicinity of the narrowed lower part, the light rays pass through the shoulder part of the hollow body into the widened upper part, but in the presence of liquid the light rays do not reach the shoulder part, the light receiver is located in the interior of the widened upper part, and means are provided to prevent access, to the light receiver, of light rays which enter through the shoulder part from directions other than predetermined directions.