Device for monitoring a predetermined level in a container

摘要

A device for monitoring a predetermined level in a container contains a sensor formed by a mechanical vibratory system comprising two vibratory rods, of which at least one vibratory rod is tubular and surrounds the other vibratory rod coaxially. Each of the two vibratory rods is secured to a common support via a resilient holding member acting as a return spring so that each rod is able to execute vibrations transversely to its longitudinal direction. An excitation arrangement causes the two vibratory rods to vibrate transversely in opposite senses at the natural resonant frequency of the mechanical vibratory system. The sensor is fitted to the container so that the tubular outer vibratory rod comes into contact with the material in the container when the material attains the level to be monitored. An evaluation circuit serves to trigger display or switching actions as a function of the vibration amplitude of the mechanical vibratory system. To compensate changes in the resonant frequency of the vibratory assembly formed by the outer vibratory rod and its resilient holding member when a deposit materializes, the inner vibratory rod is provided with a compensating mass which is shiftable in the longitudinal direction of the vibratory rod. By shifting the compensating mass the resonant frequency of the vibratory assembly formed by the inner vibratory rod and its resilient holding member can be adapted to the resonant frequency of the outer vibratory assembly.