Fluid level indicator using opto-electronic sensor - has screw insert with light guide rod exhibiting total internal reflection

摘要

The level detector comprises a threaded insert (2) which is screwed into the wall of a tank or container (8). The insert consists of a nut (28) and a cylindrical section with a hollow centre (30). A printed circuit (32) is housed in the central space and contains a light source (12) and a photo-sensitive element (18) shielded from the light source. The end of the insert which projects into the tank is in the form of a conical, light-transmitting rod (4) and in the absence of refraction at the end of the rod, total internal reflection takes place so that the detector is activated by light emitted by the source. When the end of the rod is covered by the fluid being monitored, there is no internal reflection and therefore no output from the detector. An indicator (22) shows this state.