U.S. patent application number 10/144481 was filed with the patent office on 2002-09-12 for fill level gauge.
Invention is credited to Lubbers, Wilhelm.
Application Number | 20020124644 10/144481 |
Document ID | / |
Family ID | 26005671 |
Filed Date | 2002-09-12 |
United States Patent
Application |
20020124644 |
Kind Code |
A1 |
Lubbers, Wilhelm |
September 12, 2002 |
Fill level gauge
Abstract
A fill level gauge operating by the radar principle and
preferably used for measuring the fill level of a liquid or fluid
in a container incorporates a microwave generator for generating a
microwave signal, a waveguide for conducting the microwave signal,
a horn radiator serving as a transmitting and/or receiving antenna,
an impedance transformer, and a connecting flange, where the horn
radiator is positioned on the near side of the connecting flange
facing the liquid and the impedance transformer extends at least
partially into the opening of the horn radiator. An obturator plate
is designed as an integral extension of the impedance transformer
and is positioned between the horn radiator and the connecting
flange. This design permits easy replacement of the impedance
transformer while providing a secure seal at the junction between
the horn radiator and the impedance transformer.
Inventors: |
Lubbers, Wilhelm; (Borger,
DE) |
Correspondence
Address: |
CESARI AND MCKENNA, LLP
88 BLACK FALCON AVENUE
BOSTON
MA
02210
US
|
Family ID: |
26005671 |
Appl. No.: |
10/144481 |
Filed: |
May 13, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10144481 |
May 13, 2002 |
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09851260 |
May 8, 2001 |
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6401532 |
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Current U.S.
Class: |
73/290R |
Current CPC
Class: |
G01F 23/284
20130101 |
Class at
Publication: |
73/290.00R |
International
Class: |
G01F 023/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 15, 2000 |
DE |
100 23 549.2 |
Jun 15, 2000 |
DE |
100 28 807.3 |
Claims
I claim:
1. A fill level gauge, operating by the radar principle and
preferably used for measuring the fill level of a liquid or fluid
in a container, incorporating a microwave generator for generating
a microwave signal, a waveguide for conducting the microwave
signal, a horn radiator serving as a transmitting and/or receiving
antenna, an impedance transformer, and a connecting flange, where
the horn radiator is positioned on the near side of the connecting
flange facing the liquid and the impedance transformer extends at
least partially into the opening of the horn radiator, wherein an
obturator plate is provided which is positioned between the horn
radiator and the connecting flange and which is an integral
extension of the impedance transformer.
2. The fill level gauge as in claim 1, wherein the obturator plate
covers the entire contact surface of the horn radiator.
3. The fill level gauge as in claim 1 or 2, wherein the obturator
plate and the impedance transformer consist of a chemically
resistant plastic material.
4. The fill level gauge as in claim 1 or 2 wherein, on its side
opposite the impedance transformer, the obturator plate is provided
with a waveguide insert which is an integral part of the obturator
plate and by way of which the microwave signal can be coupled into
the impedance transformer.
5. The fill level gauge as in claim 4, wherein the waveguide insert
consists of a chemically resistant plastic material.
6. The fill level gauge as in claim 1 or 2, wherein the entire
surface of the horn radiator that is in contact with the inside of
the container is coated with a dielectric.
7. The fill level gauge as in claim 6, wherein the maximum
thickness of the dielectric layer is 2 mm.
8. The fill level gauge as in claim 6, wherein the dielectric is a
ceramic material.
9. The fill level gauge as in claim 6, wherein the dielectric is a
plastic material selected from the group consisting of PTFE, PFA,
FEP and PVDF.
10. The fill level gauge as in claim 6, wherein the dielectric is
an enamel.
11. The fill level gauge as in claim 10, wherein an eyelet created
in the process of coating the horn radiator with enamel serves as a
contact for grounding the horn radiator.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of Ser. No. 09/851,260,
filed May 8, 2001, now patent No. ______.
[0002] This invention relates to a fill level gauge, employing the
radar principle, preferably for gauging the fill level of a liquid
in a container, incorporating a microwave generator for generating
a microwave signal, a waveguide for channeling the microwave
signal, a horn radiator functioning as a transmitter and/or
receiver, an impedance transformer, and a connecting flange,
whereby the horn radiator is positioned on the side of the
connecting flange facing the liquid and the impedance transformer
extends at least partially into the opening of the horn radiator. A
fill level gauge of this type has been described in the German
utility patent 94 12 243.
BACKGROUND OF THE INVENTION
[0003] Apart from the traditional mechanical float- or feeler-type
fill level gauges, fill level gauges have been in existence which
are based on a principle whereby an oscillator transmits
oscillatory waves, an oscillatory-wave detector captures the
oscillation waves reflected off the surface of a liquid in a
container, and the detected run-time of the oscillation waves
serves as a measure for determining the fill level of the liquid in
the container. In this connection, reference is made to the German
patent disclosures 42 33 324, 43 27 333 and 44 19 462.
[0004] Fill level gauges of the type mentioned are usually referred
to as non-contact fill level gauges since neither the oscillator or
oscillatory-wave detectors nor the transmitter or receiver need to
be in physical contact with the fluid. In any event, the
transmitter and the receiver do not touch the liquid unless the
container is overfilled.
[0005] All of these earlier, generally non-contact fill level
gauges work with internally transmitted oscillatory waves which are
reflected off the surface of the liquid whose fill level is to be
determined. Among these conventional fill-level determination
methods one distinguishes between those which measure the phase
shift between the transmitted and the reflected i.e. detected
waves, and those which directly measure the runtime of the
oscillatory waves. In turn, runtime-measuring systems are broken
down into fill level gauges which measure the runtime on the basis
of oscillation waves with pulse-modulated amplitudes versus those
which measure the runtime on the basis of frequency-modulated
oscillatory waves. The latter are also known as fill level gauges
employing FMCW technology.
[0006] The non-contact fill level gauges to be addressed, operating
by the radar principle, typically use a horn radiator as the
transmitting and/or receiving aerial. A waveguide generally serves
to feed the microwave signal, emanating from a microwave generator,
to the horn radiator. To permit the microwave signal traveling
through the waveguide to be transmitted via the horn radiator into
the container holding the liquid whose fill level is to be
determined, an impedance transformer is commonly used--also
referred to in the German utility patent 94 12 243 as a connecting
element--which is designed and dimensioned in such fashion that it
assures an optimally interference-free transition of the microwave
signal from the waveguide to the horn radiator with a minimum of
reflections at the junction. For that purpose, the impedance
transformer usually extends at least partially into the opening of
the horn radiator. That, however, creates a problem insofar as the
junction between the impedance transformer and the horn radiator
must be sealed if the fill level gauge is to be used in a container
that is sealed from its environment. This is necessary especially
in cases where the liquid is a chemically aggressive or corrosive
substance, a high-temperature liquid or a high-pressure fluid.
[0007] To solve the problem of having to seal the junction between
the impedance transformer and the horn radiator, the German utility
patent 94 12 243 proposes to coat the entire surface of the horn
radiator and the impedance transformer facing the liquid in the
container with a chemically resistant layer which also serves as a
seal. As an alternative, it provides for the use of an array of
O-ring seals and gaskets between the impedance transformer and the
horn radiator. These, however, are undesirable solutions in that
the impedance transformer would be solidly connected to the horn
radiator and/or an additional system of seals between the impedance
transformer and the horn radiator would be required.
SUMMARY OF THE INVENTION
[0008] It is the objective of this invention to provide a fill
level gauge of the above type, employing the radar principle, in
which the impedance transformer is easily removable and the seal
between the horn radiator and the impedance transformer can be
securely established in simple fashion.
[0009] The fill level gauge according to this invention, designed
to solve the aforementioned problem, is characterized by an
obturator plate which is positioned between the horn radiator and
the connecting flange and which is an integral part of the
impedance transformer.
[0010] As the fill level gauge is mounted on the container, i.e. at
the time the connecting flange of the fill level gauge is fastened
to the corresponding flange on the container and the flange
mounting screws are tightened, a seal is created between the
impedance transformer and the horn radiator by the pressure applied
on both sides of the obturator plate. The obturator plate forms a
tight seal between the connecting flange and the horn radiator
while at the same time no liquid can escape from the container
through the junction between the impedance transformer and the horn
radiator since the obturator plate is an integral extension of the
impedance transformer. As in the case of conventional fill level
gauges, a proper seal between the horn radiator and the flange of
the container is established by means of gaskets placed between the
contact surfaces of the container flange and the horn-radiator
flange.
[0011] The fact that the obturator plate is an integral part of the
impedance transformer not only provides a secure seal between the
horn radiator and the impedance transformer but, as a significant
advantage of this invention, it also permits easy interchanging of
a deinstalled impedance-transformer/obturator-plate assembly
without having to worry about the above-mentioned sealing
problems.
[0012] To serve its sealing purpose the obturator plate must be in
continuous, flush contact around its entire perimeter with the
contact surface of the connecting flange and with the contact
surface of the horn radiator that extends parallel to the contact
surface of the connecting flange. For all practical purposes, the
obturator plate need not cover more than a part of the contact
surface of the connecting flange and the contact surface of the
horn radiator. However, in a preferred, enhanced embodiment of this
invention, the obturator plate covers the contact surface of the
horn radiator in its entirety. This particularly large coverage
assures an even better sealing of the junction between the horn
radiator and the impedance transformer, allowing even fluids with
especially high pressures to be stored in the container without
having to be concerned about the possibility of such fluids leaking
to the outside in the area in which the fill level gauge is
connected to the container.
[0013] In general, the impedance transformer and the obturator
plate may consist of any dielectric material that offers adequate
sealing properties for the intended use of the fill level gauge.
However, in a preferred embodiment of this invention, the obturator
plate and the impedance transformer consist of a chemically
resistant plastic, preferably PTFE. When the obturator plate and
the impedance transformer are made of PTFE, one can be certain that
the seal between the horn radiator and the impedance transformer
will not spring a leak due to a corrosive effect of aggressive
chemicals on the obturator plate.
[0014] In another preferred, enhanced embodiment of this invention,
the side of the obturator plate opposite the impedance transformer
is provided with a waveguide insert which is an integral part of
the obturator plate and serves to couple the microwave signal into
the impedance transformer. The microwave signal could be coupled
into the impedance transformer without such a waveguide insert but
that would entail more significant losses or interferences in the
microwave signal at the junction. In this preferred embodiment of
the invention, the waveguide insert as well is preferably made of a
chemically resistant plastic and again preferably of PTFE.
[0015] The horn radiator usually consists of a metal such as
stainless alloy steel, tantalum, titanium or aluminum. This
invention allows the use of a metal horn radiator without any
coating. However, according to a preferred embodiment of the
invention, the entire surface of the horn radiator that is in
contact with the inside of the container is coated with a
dielectric. This assures particularly good protection of the horn
radiator against corrosion. The dielectric layer on the horn
radiator should not be more than 2 mm thick, to prevent charges on
the dielectric that would be high enough to be in conflict with
existing explosion-protection regulations. Preferred dielectric
materials include ceramic, plastic and preferably PTFE, PFA, FEP or
PVDF, as well as enamel. At this juncture it should be stressed
that, while the impedance transformer could on its part be coated
with enamel or other materials, any such enamel or other coating of
the impedance transformer is not needed for sealing purposes.
[0016] According to a preferred embodiment of this invention, the
coating or enameling process in the case of a horn radiator with an
enameled surface includes the creation of an eyelet serving as a
ground connection for the horn radiator. This not only greatly
simplifies the grounding of the horn radiator by obviating the need
for drilling a hole into the horn radiator, but it also provides a
very effective means for particularly good grounding of the
electric charges produced on the coated surface of the horn
radiator.
[0017] In connection with the enamel-coating of the horn radiator,
it should also be pointed out that the problems encountered with
prior-art enameled horn radiators, meaning a peeling or chipping of
the enamel layer due to impinging pressures, are avoided by this
invention in that sealing elements are provided not only on one
side, but on both sides of the horn radiator, which elements are
sufficiently resilient to absorb the pressures bearing on the
enamel layer. Therefore, if the connecting flange of the fill level
gauge in this embodiment is properly attached to the flange of the
container, there should be no peeling or chipping of the enamel
coating.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] There are numerous ways in which the design of the fill
level gauge according to this invention can be implemented and
further enhanced. In this context, reference is made to the
dependent claims and to the following detailed description
explaining a preferred embodiment of this invention with the aid of
the drawings, in which:
[0019] FIG. 1 is an exploded cross sectional view of the antenna
system of a fill level gauge according to a preferred embodiment of
the invention, and
[0020] FIG. 2 is a cross sectional view of the assembled antenna
system of a fill level gauge according to the preferred embodiment
of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0021] FIG. 1 shows the part of a fill level gauge according to a
preferred embodiment of this invention which is of significance in
terms of the invention, that being the antenna system of the fill
level gauge that is to be mounted on a container 1.
[0022] As shown in the figures, the fill level gauge incorporates a
waveguide 2 into which the microwave signal emanating from the
microwave generator G (FIG. 2) is coupled and which channels the
microwave signal from there. The fill level gauge further includes
a stainless-steel horn radiator 3 which, in the preferred
embodiment of the invention here described, operates as both a
transmitting and receiving antenna. Also incorporated are an
impedance transformer 4 and a connecting flange 5. The waveguide 2
not only conducts the microwave signal emanating from the microwave
generator G to the connecting flange 5 but, since the horn radiator
also functions as a receiving antenna, it also channels the
microwave signal reflected by the liquid and received by the horn
radiator 3 to the measuring transducer T (FIG. 2). The waveguide 2
leading from the microwave generator and from the measuring
transducer is positioned on the far side of the connecting flange 5
away from the liquid, while the impedance transformer 4 is located
on the near side of the connecting flange 5 facing the liquid.
[0023] As can be seen in FIG. 1, the impedance transformer 4, an
obturator plate 6 and a waveguide insert 7 constitute one
integrated unit. The waveguide insert 7 leads to the waveguide 2 by
way of a central bore 8, so that the coupling of the microwave
signal into the impedance transformer 4 takes place from the
waveguide 2 via a waveguide window 9 located on the far side of the
connecting flange 5 away from the liquid and from there via the
waveguide insert 7.
[0024] The obturator plate 6 serves as a seal between the contact
surface of the connecting flange 5 of the fill level gauge facing
the liquid and the contact surface of the horn radiator 3 away from
the liquid, while the sealing element between the contact surface
of the horn radiator 3 facing the liquid and the contact surface of
a flange 10 of the container is in the form of an O-ring gasket
11.
[0025] The horn radiator 3 of the fill level gauge illustrated in
FIGS. 1 and 2 is enamel-coated over its entire surface. The enamel
layer 12 on the waveguide 3 is 2 mm thick. For easier production,
the horn radiator 3 in the preferred embodiment of the invention
here described is enamel-coated over its entire surface. For good
corrosion protection, however, it suffices to provide enamel
coating on only those surface sections of the horn radiator 3 which
make contact with the inside of the container 1.
[0026] In the process of enamel-coating the horn radiator an eyelet
13 is usually produced. For the fill level gauge according to the
preferred embodiment of the invention as illustrated, the process
was controlled in such fashion that the eyelet 13 would be produced
at the outer perimeter of the connecting plate, meaning the part of
the horn radiator 3 that is attached between the connecting flange
5 of the fill level gauge and the flange 10 of the container 1.
That allows the eyelet 13 to be used as a direct grounding contact
for the enamel-coated horn radiator 3 by means of an electrical
conductor 14 attached to the eyelet 13 and run to the connecting
flange 5 of the fill level gauge where it is fastened with a
screw.
[0027] It will be self-evident that the above-described use of the
eyelet of the enamel layer is not limited to the fill level gauge
according to this invention but can be employed with all fill level
gauges which are provided with an enamel-coated antenna that is to
be grounded.
* * * * *