Level measuring device operating with microwave

US6087978A · kind A · utility

Assignee

• Endress+Hauser Inc. · DE

Inventors

• Robert Lalla · Bad Kötzting, DE
• Roland Muller · Weiling, DE
• Bernd Strütt · Steinen, DE

Key dates

• Filing date: Apr 21, 1999
• Grant date: Jul 11, 2000
• Expiry date: Apr 21, 2019

Classification

• Technology area (CPC G): Physics
• CPC primary: G01F23/284
• WIPO field: Measurement
• WIPO sector: Instruments

Abstract

A level measuring device suitable for highly accurate measurements. A transmission pulse generator generates microwave pulses at a transmission repetition rate and transmits them through an antenna towards a material whose level is to be measured. Echo signal from the surface of the material are received by the antenna. A reference pulse generator generates reference pulses similar to the transmission pulses but at a reference repetition rate which differs from the transmission repetition rate by a small frequency difference. The echo signal and reference pulse are input to a first mixer which generates an intermediate frequency signal that, with respect to the echo signal, is slowed by a time dilation factor equal to the quotient of the transmission repetition rate and the frequency difference. A first subcircuit samples the intermediate frequency signal, the time interval between two successive samplings equaling a time unit. A differential signal generator generates a differential signal which changes with the frequency difference. A second subcircuit determines the period of the differential signal on the basis of the time unit. An evaluation unit determines an actual time inte…