A fibre optic fluid level sensor is described based on the principle of total internal reflection and a novel packaging configuration in which the optical fibres are embedded in an optically clear material which provides for their support and protection as well as an easily cleaned surface for routine maintenance. The sensor's performance is shown to be accurately predicted from Fresnel's equations. The results of tests done in various fluids, to assess the extent of any fouling of the optical surface after prolonged exposure which might degrade the sensor's performance, are also reported.
James W . Snow,
"A Fibre Optic Fluid Level Sensor: Practical Considerations", Proc. SPIE 0954, Optical Testing and Metrology II, (16 January 1989); doi: 10.1117/12.947647; https://doi.org/10.1117/12.947647