Pulsed Light Optical Encoders
Liquid levels can be measured simply and accurately using infrared light, without the need for any electrical or thermal connection between the target and the medium.
The operating principal is illustrated in the diagram on the left. The ratio of reflective indices changes, depending on whether the tip of the sensor is surrounded by liquid or air.
If the sensor is immersed in liquid, the light rays will be deflected into the liquid and the electronics of the received changes its switching state.