Displacer transmitters are considered a direct means of level measurement.
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.
As the core position changes with liquid level, voltages are induced across the secondary windings of the LVDT. These signals are processed in the electronic circuitry and used to control the current in the 4-20 mA current loop. The enclosing tube acts as a static isolation barrier between the LVDT and the process media.