Measuring and testing – Liquid level or depth gauge – Immersible electrode type
Reexamination Certificate
1999-11-08
2001-08-07
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Liquid level or depth gauge
Immersible electrode type
C073S29000R, C324S665000, C340S620000
Reexamination Certificate
active
06269693
ABSTRACT:
This application is based on and claims the priority under 35 U.S.C. §119 of German Patent Application 198 51 213.9-35, filed on Nov. 6, 1998, the entire disclosure of which is incorporated herein by reference.
FIELD OF THE INVENTION
The invention relates to capacitive sensors in which a fluid, the characteristics of which are to be measured, forms a dielectric in one or more capacitors. The fluid may be a liquid or a gas that can enter into a hollow space between two capacitor plates.
BACKGROUND INFORMATION
Capacitive sensor devices according to the prior art are constructed as tubular capacitors or as plate capacitors.
German Utility Model Publication 19 27 694 (Bosch), published on Nov. 25, 1965, discloses an electrical capacitor with a folded sheet, tape or belt of insulating material carrying the capacitor plates or electrodes. The insulating material has metallized patterns that form the capacitor plates and conductor leads. The metallized patterns are all positioned on the same side of the tape or belt to permit a zig-zag folding pattern. Electrical connections are provided by metallized strips extending alongside the longitudinal edges of the tape or belt.
German Patent Publication DE 38 12 687 A1 (Normann et al.), published on Oct. 26, 1989 discloses a capacitive sensor for determining the filling level of a liquid in a container. Two electrodes
5
and
6
dip into the liquid. At least one of the two electrodes is provided with an electrically insulating cover layer. Two different frequencies are measured in order to ascertain the ohmic resistance and the capacitive resistance of the liquid between the electrodes. The respective signals are evaluated in a signal processing microcomputer for ascertaining the filling level as well as the water content in the liquid.
German Patent Publication DE 41 39 356 A1 (Brather), published on Jun. 3, 1993, discloses a plate capacitor for measuring of electric and dielectric characteristic values. Two covering electrodes (
1
) are spaced from each other. A central electrode (
2
) is positioned inside the space between the outer covering electrodes. The test samples to be measured are insertable into the spaces between the three electrodes.
Conventional measuring capacitors or capacitive sensors leave room for improvement especially with regard to their construction, more specifically, the ease of constructing and assemblying such capacitive sensors.
OBJECTS OF THE INVENTION
In view of the foregoing it is the aim of the invention to achieve the following objects singly or in combination:
to provide a capacitive sensor arrangement which is simple in its construction and assembly and hence can be competitively priced without sacrificing a relatively precise measurement;
to provide a measuring capacitor capable of ascertaining, for example the filling level in a container such as an oil container;
to provide a sensor probe which is rugged enough for use as an engine oil level sensor, such a sensor must assure an accurate spacing between capacitor plates even under adverse operating conditions inside an engine oil pan; and
to construct the capacitor components in such a way that a unit is formed which can be repeatedly inserted and withdrawn from a protective housing.
SUMMARY OF THE INVENTION
According to the invention metal coatings are applied to an insulating elongated support member in the form of a printed circuit board that is flexible at least along spaced sections of the elongated support member. Metal coatings are applied to sections between the flexible sections to form capacitor plates or capacitor electrodes which are spaced from each other along the elongated support member by the flexible section or sections. At least one flexible section is bent to form at least one bend with a U-configuration, whereby the capacitor plates are brought into positions facing each other across a hollow space that is maintained in a dimensionally stable state by spacers between flat or plane legs of the U-bend in which the flexible section is a curved section after bending. The metal coatings that form the capacitor plates or electrodes are secured to these plane legs of the U-configuration. Conductor leads are also secured to the support member including the curved section thereof. The spacer or spacers are preferably provided with holes through which the medium to be measured can enter into the hollow space between the capacitor plates or through which the medium can flow to form a dielectric between the plates. After bending the support member is referred to as bent circuit board (BCB).
One or more capacitors may be formed in this fashion by repeatedly bending the flexible support member to form one or more bends. Various bending configurations may be employed, for example two U-bends facing in opposite directions may form an S-configuration or an e-configuration depending on the arrangement of the bends. In the simplest configuration there is one bend with two straight legs uniformly spaced from each other and held together by the curved flexible section. Where two bends are used, three straight legs are provided in such a way that a central leg is positioned between two outer leg, whereby the central leg will carry metal coatings on both sides to form two capacitor plates or electrodes.
Preferably, the central leg of the bent configuration is provided with a stiffener. However, the two metal coatings on opposite sides of the central leg may provide a sufficient stiffness where the support member is flexible along its entire length. A tape that has relatively stiff sections spaced along its length by relatively flexible sections is quite suitable for the present purposes. In all embodiments stiffer sections are connected by bendable flexible sections to form the required bent configurations.
In a preferred embodiment the bent configuration supporting the capacitor plates and the conductor leads is mounted in a frame, preferably a frame divided into two sections that can be snapped or pinned together. Such a frame is then preferably inserted into a protective housing providing a very rugged construction. The snap-in or pin connections fix the support member and the spacer or spacers in the required dimensionally stable position relative to each other. Moreover, the cover frame protects the sensor arrangement and permits the repeated insertion and withdrawal of the sensor into and out of the protective housing.
REFERENCES:
patent: 4128857 (1978-12-01), Rayburn
patent: 4562733 (1986-01-01), Kant
patent: 5423214 (1995-06-01), Lee
patent: 1927694 (1965-11-01), None
patent: 2048626 (1982-04-01), None
Daimler-Chrysler AG
Fasse W. F.
Fasse W. G.
Larkin Daniel S.
Loo Dennis
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