Capacitive sensor arrangement for a liquid or gaseous medium, and method of making the same
First Claim
1. A capacitive sensor for measuring a characteristic of a liquid or gas, said capacitive sensor comprising at least two carrier boards carrying printed circuit elements, at least one spacer plate between said at least two carrier boards for spacing said carrier boards from each other, a hollow space in said at least one spacer plate, said printed circuit elements comprising metal coatings on inner board surfaces facing said hollow space, said metal coatings forming capacitor plates, at least one first port positioned in said sensor for said liquid or gas to enter into said hollow space inside said sensor, at least one second port positioned in said sensor spaced from said first port for permitting said liquid or gas to exit from said hollow space for pressure equalization in said hollow space relative to pressure outside said hollow space whereby, in operation, said liquid or gas forms a dielectric between said capacitor plates, and wherein said printed circuit elements further comprise conductor leads connected to said capacitor plates for retrieving sensed signals from said capacitor plates.
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Accused Products
Abstract
A capacitive sensor for measuring characteristics of liquid or gaseous media has at least two outer carrier boards and a spacer plate that keeps the two outer boards at an exact dimensionally stable spacing from each other. A sensor capacitor is formed by a hollow space in the spacer plate flanked by two metal coatings forming capacitor plates on the inwardly facing surfaces of the outer boards. Two or more capacitors can be formed by stacking the desired number of boards and spacer plates. Ports are provided for the medium to flow into the hollow space or spaces preferably in the spacer plates. Further ports for pressure equalization inside and outside the sensor are formed either laterally in spacer plate margins or directly in the outer boards. A multitude of such sensors is manufactured simultaneously by printed circuit board techniques that provide the required capacitor plate forming coatings on the inwardly facing surfaces of the boards and the required conductor leads as well as metal screening against adverse field influences. The individual plates and boards are stacked, aligned and bonded and then cut along connector strips to form the individual sensors. Lead-through contacts are formed prior to the cutting.
20 Citations
18 Claims
- 1. A capacitive sensor for measuring a characteristic of a liquid or gas, said capacitive sensor comprising at least two carrier boards carrying printed circuit elements, at least one spacer plate between said at least two carrier boards for spacing said carrier boards from each other, a hollow space in said at least one spacer plate, said printed circuit elements comprising metal coatings on inner board surfaces facing said hollow space, said metal coatings forming capacitor plates, at least one first port positioned in said sensor for said liquid or gas to enter into said hollow space inside said sensor, at least one second port positioned in said sensor spaced from said first port for permitting said liquid or gas to exit from said hollow space for pressure equalization in said hollow space relative to pressure outside said hollow space whereby, in operation, said liquid or gas forms a dielectric between said capacitor plates, and wherein said printed circuit elements further comprise conductor leads connected to said capacitor plates for retrieving sensed signals from said capacitor plates.
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13. A method for manufacturing a capacitive sensor having at least one spacer plate between two carrier boards and a hollow space formed by said spacer plate between said carrier boards carrying printed circuit elements including metal coatings forming capacitor plates facing each other across said hollow space to form a sensor capacitor for measuring a characteristic of a liquid or gas in said hollow space, said method comprising the following steps:
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(a) preparing said carrier boards by printed circuit techniques for forming said printed circuit elements including conductor leads, electrical screens and said metal coatings forming said capacitor plates, (b) providing said spacer plate with said hollow space;
(c) stacking said carrier boards and spacer plate to form a stack wherein said spacer plate is positioned between said carrier plates and wherein said capacitor plates are facing each other across said hollow space, (d) providing ports for flowing said liquid or gas into said hollow space and for pressure equalization, (e) providing said stack with first metallized lead-through contacts connecting said capacitor plates with respective ones of said conductor leads, and (f) providing said stack with second lead-through contacts connecting said electrical screens to respective other ones of said conductor leads. - View Dependent Claims (14, 15, 16, 17, 18)
(a) forming a plurality of carrier board segments on first sheets by printed circuit techniques to provide said printed circuit elements, wherein said carrier board segments are interconnected in said first sheets by lands or strips, (b) forming a plurality of hollow spaces through a second sheet thereby providing a plurality of spacer plate segments on said second sheet, wherein said spacer plate segments are interconnected in said second sheet by lands or strips, (c) providing ports for flowing said liquid or gas into said hollow spaces and for pressure equalization, (d) stacking and connecting said first and second sheets so that one second sheet is positioned between two first sheets and so that said lands or strips register with each other in a stack of a plurality of sheets forming a multilayer panel, (e) providing said lead-through contacts through said sheets in said multilayer panel, and (f) severing said multilayer panel along said lands or strips to form a multitude of said capacitive sensors.
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16. The method of claim 15, further comprising the step of temporarily filling said plurality of hollow spaces with a filler material (13) for preventing deformations of said carrier boards and spacer panels during said connecting step, performing said connecting step, and then removing said filler material.
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17. The method of claim 16, wherein said filler material is a strip (13) of PTFE (polytetrafluoroethylene) which is removed after said connecting step and said severing step have been performed.
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18. The method of claim 15, wherein said connecting step is performed as an adhesive bonding step.
Specification