What type of level sensor requires an air supply to operate?

A bubbler tube level sensor operates by using a small air supply to create bubbles in a liquid. The air is introduced through a tube that extends into the liquid, and as the pressure within the tube changes due to the liquid level, it causes a change in the flow of air bubbles. These air bubbles rise through the liquid, and the pressure reading at the bottom of the tube indicates the level of the liquid above it. This method is especially useful for measuring levels in high-pressure or turbulent environments where other types of sensors might not perform reliably.

In contrast, ultrasonic sensors use sound waves to measure distances and don't rely on air supply; they emit ultrasonic waves and calculate the time taken for the echoes to return, thus determining the level of the liquid. Capacitance sensors detect changes in capacitance caused by the level of a liquid, and they need no air supply for operation. Float switches use a buoyant object that rises and falls with the liquid level to open or close a switch, also requiring no external air source.