Measuring and testing – Liquid level or depth gauge
Reexamination Certificate
2001-09-13
2004-01-27
Williams, Hezron (Department: 2856)
Measuring and testing
Liquid level or depth gauge
C073S30400R, C342S124000
Reexamination Certificate
active
06681626
ABSTRACT:
TECHNICAL FIELD
The invention relates to a connection piece for a level metering device working on the guided microwave principle, with said level metering device comprising a single-wire line. A connection piece of this type comprises an upper connection piece part and a connection piece wall disposed below said upper connection piece part, said upper connection piece part having a connection piece wall height. Said upper part of the connection piece is configured so as to allow for the attachment of a level metering device working on the guided microwave principle, said level metering device having a single electrical conductor or a single electric line.
Such connection pieces are in particular mounted in receptacles such as tanks, reservoirs for any kinds of filling products, open receptacles, etc. Connection pieces of the herein mentioned kind can, however, be used in floor or wall elements.
The invention further relates to a combination of a level metering device working on the guided microwave principle and having a single single-wire line for guiding the microwave to the filling product to be measured, and an interference-reducing attachment means such as a connection piece or a flange, on which the level metering device is mounted.
In this context, it is the question of a guided microwave—also called “Time Domain Reflectometry (TDR)”—when high-frequency microwave pulses are guided along an electrical conductor. Such an electrical conductor can be, for example, a wire, a steel cable, or also a metal rod. The electrical conductor extends up to the filling product. When impinging on the surface of the filling product, the microwave pulses are reflected. The transit time of the pulses is evaluated by the electronic unit integrated in the most cases in the level metering device, and is outputted as the filling level. By means of such level metering devices, the filling levels of all kinds of bulk goods but also of fluids and liquids can be measured. The advantage of these level metering devices resides in that the density, conductivity and dielectricity of the filling product do not impede the measurements. Even changing bulk good properties cannot influence the measured value. Thus, in particular, lime, cement, cereals, plastics pellets, flour and gravel can also be measured by means of level metering devices of the mentioned kind. The filling level is also reliably detected in filling products exhibiting a changing humidity or varying dielectricity. In particular, even high, tapered receptacles, in which contact-free measurement procedures often exhibit difficulties, can be measured by means of the mentioned level metering devices without any problem. One level metering device of this type is, for example, distributed under the designation Vegaflex. In this respect, it is to be noted that the term “level metering device” also includes devices, the evaluating electronic unit of which is not directly integrated into a housing of the level metering device but is accommodated at another location.
PRIOR ART
Level metering devices of the above-mentioned kind are often mounted in connection pieces of a receptacle containing a filling product. For receiving a level metering device of the above-described kind, such connection pieces are basically comprised of an upper connection piece part in the form of a flange plate having a central bore therethrough, and a connection piece wall disposed therebelow, such as a tube piece, for example. The connection piece wall may be configured cylindrical in its cross-section or also polygonal. In most cases, said connection pieces are made of metal, and the upper connection piece part and the connection piece wall are correspondingly welded together in most cases. Of course, different connection techniques can also be employed for these connection piece parts depending on the field of application. Even a one-part configuration could be considered.
When a level metering device working on the guided microwave principle, is mounted into a connection piece, then superpositions arise in the so-called echo profile curve. These superpositions depend in particular on the connection piece radius and can propagate over several meters beyond the end of the connection piece, i.e. the free edge of the connection piece wall. With very small or even with very large connection piece radii, no or only relatively small superpositions arise, but such interfering superpositions are frequent with the connection piece sizes present in the industrial plant engineering. The superpositions complicate or even render a detection of smaller echoes impossible. Thus, in particular directly at the end of the connection piece or in the close neighborhood thereof, echoes cannot be or can only be hardly detected. In the worst case, such superpositions can have the effect that a reasonable level metering cannot be effected.
For eliminating this problem, it is already known to use a so-called horn which surrounds the level metering device at least in the area of the connection piece. In this respect, reference is made, for example, to DE 44 04 745 A1. In the therein shown device for level metering, a transmitter and receiver means and a single conductor extending into the filling product to be measured is present. Said transmitter and receiver means is connected with the single conductor via a coaxial line. In this configuration, electromagnetic waves emitted by the transmitter are guided through the single conductor towards the filling product, are reflected by the surface thereof and detected by the receiver means. By means of a matching funnel made of electrically conductive material, attached to a mounting flange, an impedance matching between the coaxial line and the single conductor is achieved, thus reducing reflection during transmission of the measurement signal. The matching funnel hereby comprises a funnel-type contour expanding towards the surface of the filling product.
From EP 0 780 664 A2, a sensor device for level metering is likewise known, wherein the signal emitted by a transmitter means is guided up to the filling product via a conductive rod. In this case, the rod is connected to the receptacle via a system of several flanges which could be interpreted as connection pieces.
It is also known to provide two parallel lines instead of the single-wire line; in this case, however, it is the question of a level metering device working on the guided microwave principle comprising a two-wire line. It is moreover known to provide a coaxial line instead of the single-wire line.
All these known solutions require large expenditures and are expensive to produce and are also difficult to mount. Thus, it is necessary, in particular with the level metering device comprising two lines, to provide spacers in regular intervals so as to ensure that said two lines always exhibit exactly the same distance therebetween. These spacers, however, generate interfering reflections and hence measurement inaccuracies. It may also be the case that deposits settle between two lines, a fact which could lead to a failure or inaccuracies of the measurement. The same applies to the solution using a coaxial line. The coaxial line has further the problem of not being usable in case of bulk goods.
DESCRIPTION OF THE INVENTION
The invention is therefore based on the technical problem of providing a connection piece, which is simple and cost-efficient to produce and, nevertheless causes minor interfering effects when being used in combination with a level metering device comprising a single-wire line and working on the guided microwave principle.
The invention is further based on the technical problem of providing a combination of a level metering device comprising a single-wire line and working on the guided microwave principle, and an attachment means such as, for example, a connection piece, serving for attaching the level metering device on a receptacle, with said combination of level metering device and attachment means being supposed to cause less interferences than hitherto.
The first mentio
Jackson André K.
Schwegman Lundberg Woessner & Kluth P.A.
VEGA Grieshaber KG
Williams Hezron
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