Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Distributive type parameters
Patent
1994-03-02
1996-08-06
Wieder, Kenneth A.
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Distributive type parameters
324631, 324637, 324642, 342124, G01F 2328, G01R 2704
Patent
active
055437206
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a device for gauging the level of a fluid, that is, a flowing or granulate material, contained preferably in a container, comprising a transmitter for the transmission of a polarizable microwave signal through a first waveguide section, a receiver for receiving a reflected microwave signal, an electronic unit, arranged to determine the reflex position of the reflected microwave signal and an antenna means with a second waveguide section.
Such devices have been used for a long time, operating in the radar wavelength area, and recently, devices with very high measuring accuracy (e.g. 0.01%) have entered the market Typical users of such equipment are oil refineries and petrochemical industry, where level gauging takes place in large tanks. In such applications numerous various antennae or corresponding tank adaptions are required, depending on the construction of the tank. However, it is much desired, that the same type of electronic unit with transmitter and receiver can be used in those different tank constructions.
A number of contradictory demands on a device of the kind mentioned in the introduction exist in practice: circularly polarized wave is suitable, is useful, extent this tube is partly located outside the tank, the leaking of electromagnetic waves must be limited, while at the same time, the sensitivity in gauging demands a certain signal level, reception occur in different polarizations in order to reduce the effect of internal antenna echoes.
In addition to its ordinary function, the ante means usually comprises a sealing function and must therefore be permanently installed, and is usually rather heavy. This means that a device of the kind mentioned in the introduction cannot meet all the contradictory demands mentioned above.
The object of this invention is therefore to achieve a device of the kind mentioned in the introduction, which in a simple way admits adaption to existing tank constructions with their various demands on the equipment in order that level gauging with high accuracy shall be achieved by using one and the same electronic unit. The device shall also be inexpensive to acquire.
According to the invention such a device is primarily characterized in that the transmitter and receiver are arranged respectively to transmit and receive microwave signals in their respective waveguide mode, which are mutually orthogonal, that is, mutually independent, and by a third waveguide section inserted between the first and second waveguide sections, and provided with means to act upon said microwave signal through polarization and/or damping for optimal adaption of the device to various containers and antennae, the first waveguide section being preferably circular in cross section. Suitably, the waveguide modes mentioned are linearly polarized, mutually perpendicular.
According to an embodiment of the invention a third waveguide section is provided with a dielectric plate set at an angle of 45.degree. to the extension plane of the transmitted microwave to achieve various elliptic polarizations, of which right and left turned circular polarizations are typical. Thereby, a double circular polarization of the microwave can be obtained, suitable for a horn antenna. At reflection in the measuring surface the circular polarization is switched (+ to - or - to +) and on re-entrance through the third waveguide section a perpendicular linear polarization is obtained. The advantage is gained, that the portion of the transmitted microwave signal that is reflected against a wall is suppressed in that it is reflected one extra time and then gives a linear polarization in the transmitted polarization. In an alternative embodiment polarization of a third waveguide section is achieved with elliptic cross section or provided with internal ridges.
In another embodiment of the invention the third waveguide section comprises instead one or two plates of damping material, whereby the transmitted microwave signal is damped considerably (e.g. 20 dB) without the re-reflected signal bein
REFERENCES:
patent: 2933731 (1960-04-01), Foster et al.
patent: 4087746 (1978-05-01), Kanae
patent: 4353041 (1982-10-01), Bryans et al.
patent: 5136299 (1992-08-01), Edvardsson
patent: 5351036 (1994-09-01), Brown et al.
Brown Glenn W.
SAAB Marine Electronics AB
Wieder Kenneth A.
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