Communications: directive radio wave systems and devices (e.g. – Determining distance – Material level within container
Patent
1991-06-06
1992-08-04
Barron, Jr., Gilberto
Communications: directive radio wave systems and devices (e.g.,
Determining distance
Material level within container
342188, 367908, 73290V, G01S 1308, G01F 2328
Patent
active
051362996
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a device for gauging the level of a fluid in a container, i.e. a fluent for granulate material, preferably a condensable gas under overpressure, comprising a vertical tube through which a number of relatively small openings in its wall so communicate with said fluid that its level is the same in the tube as in the container, further a transmitter for feeding a polarizable microwave signal through the said tube, its cross section being so big that it admits passage of the microwave signal, further a receive of reflected microwave signal and an electronic unit arranged to determine the reflex position of the reflected microwave signal.
Such devices have become more and more important particularly for petroleum products such as crude oil and products manufactured therefrom. By containers it is meant in this context large containers constituting parts of the total loading volume of a tanker, or even larger usually circular-cylindrical landbased tanks with volumes of tens or thousands of cubic meters. Demands on accuracy of measurement have become higher. This has brought about, for instance, that level gauging in containers that contain condensable gas under overpressure, such as natural gas, butane or propane, places particularly high demands on the gauging equipment used. When ordinary petroleum products are used, i.e. such that are fluent at the usual temperatures, it is possible to open the container even when it is filled to a greater or less degree with the product in question, and through this a calibration of the gauge can be effected without too much work.
When to gauge the level in a container that contains condensable gas under overpressure it is possible only exceptionally to open such a container and make a calibration. In addition, because the velocity of propagation of the microwave signal depends on the pressure in the gas there is a great need for an arrangement for calibrating a device of the kind mentioned in the introduction.
According to the invention a device of the kind mentioned in the introduction, which can be calibrated in a simple manner also when the said container contains a condensable gas under overpressure, is characterized primarily by a polarization means, arranged optionally to polarize the microwave signal emitted from the transmitter in a first and a second polarization plane, which form a mutual angle, preferably 90.degree., and further by at least one reflecting reactance arranged in the tube to give a substantially stronger reflex of the microwave signal in the first polarization plane than in the second.
The said tube is usually circular-cylindrical, but other embodiments are also possible provided they show 90.degree. symmetry in cross section, such as a square or super-elliptical cross section with two equally long major axes. As a polarizable microwave signal, such is preferably used as shows H.sub.11 mode, but also other rotary unsymmetrical modes, such as E.sub.11 mode, are conceivable. In practice, the cross section of the tube is often dimensioned so that it admits passage of higher modes. In a preferred embodiment of the device according to the invention the transmitter comprises a circular waveguide for one-mode propagation, primary for H.sub.11 mode.
The polarization means can in a known manner be formed in many different ways. In a suitable embodiment it consists of a substantially plane plate of a dielectric material such as a polymer, arranged with its plane substantially parallel to the symmetry axis of the waveguide, preferably crosswise filling out the diameter of the waveguide, the waveguide having suitably a circular cross section. The plate is arranged turnable about the symmetry axis of the waveguide between two positions, preferably so that the planes of the plate in the two positions form 45.degree..
In an alternative preferred embodiment of the polarization means the plate of dielectric material is replaced by one or two plane metal plates, they too being placed with their planes substantially parallel to the symm
REFERENCES:
patent: 3394589 (1968-07-01), Tomioka
patent: 4170765 (1979-10-01), Austin et al.
patent: 4641139 (1987-02-01), Edvardsson
patent: 5070730 (1991-12-01), Edvardsson
Barron Jr. Gilberto
Saab Marine Electronics Aktiebolag
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