Method and apparatus for radar-based level gauging

Abstract

A method for radar-based gauging of the level of a substance in a tank (13) having at least one interfering structure, e.g. a beam (16a); an agitator (16b) or a tank side wall (16c), comprises transmitting a microwave signal in a predetermined polarization state (LHCP) towards the surface (14) of the substance and the at least one interfering structure; detecting, separately in two different polarization states (LHCP, RHCP), microwave signals (32, 33, 34) as reflected against the surf ace of the substance and against the at least one interfering structure; distinguishing based on signal strengths of the microwave signals detected separately in the two different polarization states, the detected microwave signal (32), which has been reflected against the surface of the substance; and calculating based on a propagation time of the distinguished microwave signal the level of the substance in the tank.

Description

[0001] The invention relates generally to level gauging, and more specifically the invention relates to a method and an apparatus for radar-based level gauging.BACKGROUND OF THE INVENTION AND RELATED ART[0002] Radar-based methods are extensively used for level gauging, i.e. measuring a distance from the top of a tank to a surface of a liquid, or some kind of granular solid stored in the tank, by means of transmitting microwaves towards the surface of the liquid or the granular solid, receiving the microwaves as reflected against the surface of the liquid or solid, i.e. the surface echo, and calculating the level of the liquid or solid in the tank from the propagation time of the transmitted and reflected microwaves.[0003] One very general problem in this respect is that the tank includes typically various structures, such as beams, support beams, pipes, agitators, tank walls, etc. Such structures may also reflect microwaves,. and such echoes can interfere with the microwaves reflect...

AI Technical Summary

Benefits of technology

[0010] A still further object of the invention is to provide such a method and such an apparatus, which are reliable, efficient, accurate, and precise.

[0018] By means of the present invention a very robust routine for distinguishing detected microwave signals, which have been reflected against the surface of the substance gauged, may he implemented. As compared to prior art devices the invention provides for measurement in more disturbing environments, i.e. where more interfering echoes do occur, with higher accuracy. For instance, microwave signals reflected at the surface of the substance, may be distinguished despite being weaker to much weaker than a microwave signal as reflected against an interfering structure.

Problems solved by technology

One very general problem in this respect is that the tank includes typically various structures, such as beams, support beams, pipes, agitators, tank walls, etc.

Such structures may also reflect microwaves,. and such echoes can interfere with the microwaves reflected from the surface of the liquid or solid, the level of which being gauged.

An interfering echo having a signal strength considerably lower than the signal strength of the surface echo will cause measuring errors if the structures creating the interfering echoes is close to, i.e. within a few tenths of a meter from, the surface.

Various echo logic methods have been applied to decrease this risk, but nevertheless this is a large problem in many tank environments.

Furthermore when the echo from the surface is close to a disturbing echo there is a risk for a large measuring error.

Using prior art equipment large measuring errors cannot be avoided if the disturbing echo is close to the surface echo and of comparable strength.

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