Patent ID: 6047598
Filing Date: 2000-04-11
Classification: G01F,Y10S

Abstract:
An arrangement for measuring the contents level in a container comprisinga level measuring device for continuously measuring the contents level and which is a distance meter functioning in accordance with the transit time principle,the level measuring device has a contents level sensor which transmits waves from a position located above the highest possible contents level to the surface of the material in the container, receives echo waves reflected from the surface of the material in the container, and gives an electric output signal representing the echo waves, andhas a measuring circuit which forms a current echo function from the output signal of the contents level sensor representing the echo amplitudes as a function of distance over the whole measuring range, compares a portion of the current echo function to a stored empty echo function to determine a measured value of the contents level, and, when triggered, compares the measured value of the contents level to a predefined level, anda plurality of limit sensors located at the container to monitor different contents levels between the minimum and maximum contents levels of the container, each limit sensor supplying an output signal to the measuring circuit indicating whether the contents level in the container is above or below a respective predefined level monitored by each limit sensor,wherein, when a first limit sensor of the plurality of limit sensors indicates that the contents level is above a first predefined level and a second limit sensor of the plurality of limit sensors indicates that the contents level is below a second predefined level, the measuring circuit comparesthat part of each current echo function situated in the range between the first predefined level and the second predefined level, withthe stored empty echo function to determine a useful echo wave reflected from the surface of the material in the container and determine the measured value of the contents level from the transit time of the useful echo wave, andwherein, when the output signal of one of the plurality of limit sensors changes status, the measuring circuit performs a level comparison comparingthe predefined level monitored by the changed one of the plurality of limit sensors withthe measured value of the contents level determined at the same time by themeasuring circuit from the transit time of the useful echo wave in order to determine an error in the contents level measurement carried out by the level measuring device.