A displacer level transmitter is a type of level measurement device used to determine the level of liquids in a tank or vessel. It operates on the principle of buoyancy, which is the upward force that a fluid exerts on an object that is partially or completely immersed in it. The displacer level transmitter consists of a probe, called a displacer, which is suspended from a spring and positioned inside the tank or vessel. As the level of the liquid in the tank changes, the buoyancy force acting on the displacer also changes, causing it to move up or down. This movement is detected by the transmitter, which converts it into a proportional level measurement, typically output as an analog or digital signal. Displacer level transmitters are highly accurate and reliable, and they are commonly used in applications where precise level measurement is critical, such as in the oil and gas, chemical processing, and water treatment industries. They can also be used in hazardous environments, as they can be constructed with explosion-proof enclosures and are compatible with a wide range of liquids. Displacer level transmitters can be used in conjunction with other instruments such as control valves to provide closed-loop level control.