Measuring and testing – Fluid pressure gauge – Diaphragm
Reexamination Certificate
1999-04-16
2002-07-30
Fuller, Benjamin R. (Department: 2855)
Measuring and testing
Fluid pressure gauge
Diaphragm
Reexamination Certificate
active
06425289
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This application relates to the field of electronic sensors and more particularly to the field of capacitive sensors for measuring flow and pressure.
2. Description of Related Art
A capacitive sensor for measuring pressure and flow of liquids and gases typically includes a first electrode located remote from a second electrode, with the first and the second electrodes forming a measurement capacitance. At least the first electrode is formed as a membrane which can be deformed by a pressure applied to the membrane.
A sensor of this type is described in DE 33 10 643 and can be employed for measuring both absolute and relative pressures. The sensor, however, cannot provide any additional and/or more detailed information. It is therefore desirable to provide a capacitive sensor which can provide differentiated information about a measurement quantity.
SUMMARY OF THE INVENTION
In general, according to one aspect of the invention, at least one electrode of a sensor of this type is formed with a spatial structure to allow measurements providing spatial resolution.
By measuring a spatially differentiated capacitance value or capacitance values of the electrodes, a significantly improved differentiated information about measurement quantity or also about the condition of the sensor itself can be obtained. For example, a flow profile of a fluid or a gas flowing through the measurement capacitor can be determined and also displayed based on the spatial distribution of the capacitance. In addition, such an arrangement also provides improved information about the relative spatial arrangement of the electrodes, since any deviation from a mutual parallel alignment or a relative parallel displacement of the electrodes relative to one another can be readily observed and can therefore be taken into account when evaluating the measurement signals. Furthermore, the spatially resolved measurements and the detected relative position or change in position of the electrodes can also be used to recognize fatigue of the capacitive sensor; to assess the reliability of the measurement itself, and to also estimate the remaining lifetime of the sensor. The sensor of the invention can then be replaced with a functional sensor before a malfunction may indeed occur.
With the spatially structured electrode which includes a plurality of electrode elements that are spaced apart from each other and arranged in a two-dimensional pattern, the measurement results can be spatially resolved. By arranging the electrode elements in the two dimensions, the measurement results can be spatially resolved not only in one direction, but in a plane that is defined by the surface of the substrate. The individual electrode elements may be advantageously arranged in form of a checkerboard pattern and may be identical with respect to their physical properties (size, material, and so on).
The measurement signals derived from the individual elements are essentially identical if the counter electrode has comparable characteristic properties, so that the signals can be easily evaluated to provide the desired spatial resolution. Consequently, the difference in the measurement signals is essentially determined by the spatially differentiated structure of the quantity to be measured and/or by the spatially changing structure of the sensor itself. Although the surface area of the elements is reduced by the two-dimensional arrangement of the electrode elements, causing a proportional reduction in the measurement capacitance, this disadvantage can be overcome by a suitable choice of the signal amplifiers and/or the electronic processing unit. This disadvantage, however, is acceptable, if a two-dimensional spatially differentiated measurement signal is desired.
According to one advantageous embodiment of the invention, the spatially structured electrode is formed of several mutually parallel stripes. By arranging the differentiated spatial structure in the form of parallel stripe-shaped elements, a spatial resolution corresponding to the two-dimensional spacing between adjacent stripe-shaped element can be attained. In addition, the surface area and therefore also the capacitance of the stripe-shaped elements can be made quite large, thereby improving the reliability of the measurement signals. The capacitance is proportional to the area of the stripe-shaped element. Consequently, the capacitive measurement signal may subsequently require only a small amount of signal amplification, which improves the signal-to-noise ratio of the spatially differentiated measurement signal.
According to another advantageous embodiment of the invention, the spaced-apart elements arranged in a two-dimensional pattern may have the form of circles or rectangles. With this arrangement of the electrode elements, the elements can be closely spaced to provide a large surface coverage. This would not be possible if the shape of each element were selected individually. Circularly or rectangularly shaped electrode elements arranged in a two-dimensional arrangement therefore advantageously have large capacitance values which improves the signal quality and the overall reliability of the measurements.
According to yet another embodiment of the invention, an electronic circuit for processing the measurement signals is integrated with one of the substrate members, wherein the integrated circuit is preferably located underneath the electrode of the respective substrate member. With this integration, in particular in the vertical direction, of the capacitive sensor with the electronic circuit for processing the measurement signals, the space taken up by the sensor is used much more efficiently. Consequently, the overall footprint of the system decreases proportional to the increased packing density of the entire system, which includes the capacitive sensor and the electronic processing unit. In addition, the length of the signal path that the measurement signals of the capacitive sensor have to travel, is also reduced. This feature reduces possible interference and improves the accuracy of the quantities to be measured and processed by the capacitive sensor.
According to yet another advantageous embodiment, the integrated electronic circuit includes devices which can separately process the measurement signal having the spatial resolution. The devices are preferably arranged in close proximity to the individual electrode elements of the spatially structured electrode. In this way, the spatially resolved signals can be processed with devices that are identical or at least substantially identical, so that the measurement signals can be processed by a cascaded electronic system. The cascaded arrangement can be expected to reduce not only the costs of developing such a signal processing system, but also the expenses associated with a potential malfunction of the spatially resolving processor units, since this system is more complex and may fail more frequently than conventional capacitive sensors. Moreover, a common central processor that receives the signals processed by the individual devices, can be used for commonly processing the measurement signals, since each of the measurement signals is generated by a processing unit having an identical or essentially identical processor characteristics. The close proximity between the electrode elements and the processing devices also minimizes possible signal losses. Consequently, the decrease in the surface area of the individual electrode elements is not significant in view of the ability to produce a spatially differentiated measurement signal.
According to still another embodiment of the invention, the electronic circuit and/or devices capable of processing signals with a spatial resolution may include amplifier devices that are preferably arranged proximate to the electrode elements of the spatially structured electrode. In this case, the un-amplified measurement signal travels only a very short signal path to the respective signal amplifier or signal processor associated with
Giehl Juergen
Igel Guenter
Sieben Ulrich
Aw-musse Abdullahi
Foley & Hoag LLP
Fuller Benjamin R.
Micronas GmbH
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