The RS PRO PW40 series ultrasonic level/distance sensors are non-contact devices, which means they do not require physical contact with the target object. This characteristic makes them suitable for applications where contact is impractical or undesirable. They can be used to detect objects made from various materials regardless of their shape, colour, or surface contour. They operate using high-frequency sound waves that are inaudible to the human ear.

In general, ultrasonic level sensors use ultrasonic waves to measure the distance or level of a target substance, such as liquid or solid material. The sensor emits ultrasonic waves and measures the time it takes for the waves to return after being reflected by the target.