| 摘要 |
A U-shaped device wherein the presence or absence of a transparent liquid or solid between the legs of the U is sensed. The device utilizes a collimated light source mounted in one leg of the U with an associated limited field of view sensor in the other leg of the U-shaped device. The light source is placed so as to cause the transmitted light beam to strike the surface of the material to be sensed at an angle which is substantially off of a line perpendicular to the surface of the sensed material. The light sensor is placed so as to receive the light beam when there is no liquid or solid material present between the source and the sensor and to prevent the refractively bent light beam from striking the sensor when a transparent liquid or solid is placed between the light source and sensor. The presence or absence of a transparent liquid or solid between the light source and sensor is indicated by an electronic circuit which provides current pulses to drive the light source and amplifies the light sensor current sufficiently to be able to drive a visible light emitting diode or acoustic warning device.
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