Communications: directive radio wave systems and devices (e.g. – Determining distance – Material level within container
Reexamination Certificate
1999-03-12
2001-02-06
Gregory, Bernarr E. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Determining distance
Material level within container
C342S118000, C324S642000, C324S644000, C073S29000R, C073S30400R
Reexamination Certificate
active
06184818
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority of application No. 198 10 601.7 filed in Germany on Mar. 12, 1998, the rights of priority of which are claimed and the subject matter of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a level measuring arrangement for measuring the liquid level in a tank by using a microwave transmitting/receiving devices and a waveguide that extends into the tank for guiding a coupled-in microwave.
In addition to mechanical measuring methods using floaters, arrangements for measuring the liquid level in tanks are known and are used primarily in large tank plants and tank plants with floating lids. These arrangements use microwave radiation to determine the distance to the liquid, and thus the liquid level, from the echoes reflected by the liquid surface. The measuring accuracy is in the millimeter range to centimeter range.
An arrangement of the above type is shown in U.S. Pat. No. 5,136,299, in which a microwave transmitter excites a wave in a first hollow conductor segment. A specific polarization direction of the electric field vector is forcibly imposed on this wave by means of a polarizing plate. The polarized wave travels from the first hollow conductor segment via a transition piece into a measuring tube having a considerably larger diameter. The measuring tube has a plurality of openings along a casing line to allow an interchange with the surrounding liquid, so that it is ensured that the filling level inside the measuring tube is equal to the surrounding filling level. The tube also functions as a settling tube (stilling well) to balance rapid fluctuations of the liquid surface.
The measuring tube functions as a hollow conductor for the coupled-in microwave. For specific types of oscillation, the large tube cross section can provide propagation conditions with particularly low losses. However, it also allows for the propagation of various modes with potentially different propagation speeds. Depending on the excited type of oscillation, the openings serving as interruptions in the tube wall can, moreover, influence the propagation conditions, so that the signal analysis in the microwave device cannot be scaled linearly to the filling level despite the calibration markings that are provided. In particular, the propagation conditions in the measuring operation and the calibration operation can differ with the known arrangement.
SUMMARY OF THE INVENTION
It is therefore the object of the invention to specify an arrangement of the aforementioned type which, while requiring little expenditure, makes it possible to obtain an exact and in particular scalable level measuring with high precision.
With the above objects in view, the present invention resides in the provision of measuring arrangement of the above type in which the wave guide has clear and constant wave propagation characteristics for a wave with the operating frequency.
As a result of the unambiguous and constant waveguide propagation characteristics, as referred to the operating frequency, the echo delay time of the microwave signal can be imaged unambiguously and linearly on the filling level. The arrangement can be set up inexpensively since commercially available radar level sensors without mode adapter can be used.
REFERENCES:
patent: 4566321 (1986-01-01), Zacchio
patent: 4670754 (1987-06-01), Zacchio
patent: 5136299 (1992-08-01), Edvardsson
patent: 5148177 (1992-09-01), Nagamune et al.
patent: 5182565 (1993-01-01), Nagamune et al.
patent: 5365178 (1994-11-01), Van Der Pol
patent: 5609059 (1997-03-01), McEwan
Daimler-Chrysler AG
Gregory Bernarr E.
Kinberg Robert
Venable
Voorhees Catherine
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