In a method of optically determining a level of liquid in a liquid-filled container
a light guide body projects into the container. The light guide body has an end
face for the entry and exit of light and stepped side faces forming separate reflection
faces. The light is totally reflected at those reflection faces which are not immersed
in the liquid but refracted into the liquid at immersed reflection faces. The totally
reflected light is reflected back to the end face. The intensity of the light beam
reflected totally by each reflection face back to the end face is measured separately.
Measurement signals for determining the filling level are subjected to plausibility
checking to recognise and eliminate measurement faults and errors. The invention
can be used for determining the level of liquid in a container or tank for fuel,
washing water, oil, hydraulic fluid and the like in a motor vehicle.
