The displacer rod, which is attached to a measuring spring by a chain, immerses into the liquid and is subject to a buoyant force proportional to the mass of the displaced liquid.
Every change in the weight of the rod corresponds to a change in the length of the spring and is therefore a measure of the liquid level.
The longitudinal expansion of the spring, i.e. the travel of the rod, will be transmitted from the measuring space to the indicator unit by means of a magnetic coupling. The basic version of the indicator unit consists of a scale with a pointer for displaying the liquid level.
As an option, the indicator unit may be equipped with electrical transmitters for remote display or with limit switches. If the device cannot be installed from above, because, for example, a stirrer is mounted in the container, a special displacement vessel is available for lateral installation.
Since the buoyancy of the displacer rod depends on the density (g /L or kg/m3) of the measured medium, it must have been designed for the specific liquid to be measured.