As the liquid level in the vessel increases or decreases, the buoyancy force on the displacer increases or decreases. The motion created by the change in force acting on the range spring, causes movement of an attraction ball within an enclosed pressure-boundary tube.
Displacer switch operation is based upon simple buoyancy, whereby a spring is loaded with weighted displacers, which are heavier than the liquid. Immersion of the displacers in the liquid results in buoyancy force change, changing the net force acting on the spring. The spring compresses as the buoyancy force increases.
Electronic displacer level transmitter technology operates by detecting changes in buoyancy force caused by liquid level change. These forces act upon the spring supported displacer causing vertical motion of the core within a linear variable differential transformer.