The FL50 Liquid Level Sensor is an NPT Plastic Point Liquid Level Sensor. This water/fluid detector with Nylon or Polypropylene (PP) housing can accommodate a wide range of liquids and has no moving parts. This Ultrasonic Gap sensor is ideal for harsh environments. Ultrasonic level sensors work by emitting high-frequency sound waves and detecting changes in the waves as they bounce back to the sensor, making them appropriate for both point level and continuous sensing applications.