Q: How does it work?

A: The Pillar Point Electronics Universal Fluid Sensor (UFS) uses a miniaturized infrared (IR) emitter and detector built into a tiny microprocessor-driven electronic circuit potted into a fitting, as shown in the sketch. Two versions of the UFS are available: the UFS-T and the UFS-AN. The UFS-T is a UFS mounted in a custom made tee and is designed for in-line applications. The UFS-AN is a modified AN912-2D bushing and is designed for in-tank applications. A clear, cylindrical cast acrylic prism is potted into the fitting in contact with the fuel or other non-particulate bearing liquid.

The sensor works on the principle of internal reflection in the prism. Since the index of refraction of the prism and air are very different, when the end of the prism is not immersed in the liquid, the IR light is internally reflected back towards the IR detector. When the detector "sees" the IR light, the output(s) of the circuit can illuminate a warning light (or activate other devices.) When the prism portion of the sensor is immersed in the liquid, the refractive indices nearly match, so IR light escapes from the prism and into fuel.