Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
1999-09-07
2002-10-15
Le, N. (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C324S658000
Reexamination Certificate
active
06466036
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention pertains to the sensing or measurement of electrical capacitance, and in particular to the sensing an object's proximity to or contact with a sense plate connected to a capacitance measurement circuit
2. Background Information
In his U.S. Pat. No. 5,730,165, the inventor teaches a capacitive field sensor employing a single coupling plate and a method of detecting a change in capacitance of the coupling plate, Cx, to ground. The apparatus taught in U.S. Pat. No. 5,730,165 comprises pulse circuitry for charging the coupling plate and for subsequently transferring the charge from the plate into a charge detector, which may be a sampling capacitor, Cs. The transferring operation is carried out by means of a transfer switch electrically connected between the coupling plate and the charge detector. The disclosure of U.S. Pat. No. 5,730,165 is herein incorporated by reference.
In U.S. Pat. No. 4,806,846, Kerber teaches a pulse circuit for measuring an unknown capacitance. His arrangement is characterized by careful elimination of effects of stray capacitances, such as a capacitance to ground. Kerber employs two clocked switches and a buffer amplifier to charge and discharge the capacitor under test.
BRIEF SUMMARY OF THE INVENTION
The invention provides apparatus and method for measuring an absolute or relative value of the capacitance of a capacitor or other element having the electrical property of capacitance, as well as for measuring changes in a capacitive value. In many uses of interest, a change in the capacitance to ground of a sense plate is measured and a control output is generated responsive to the change.
A feature of some embodiments of the invention is the provision of novel pulse circuitry for measuring capacitance to ground, the circuitry comprising a plurality of electrical switching elements, each of which has one side electrically connected to either a power supply voltage or to a circuit ground point. This circuit arrangement is more compatible with available integrated circuit design and manufacturing practices than is prior art pulse circuitry, which commonly had one side of at least one switching element floating. These improved arrangements thereby provide superior performance at a lower manufacturing cost.
Another aspect of the invention is that it provides a proximity sensing means having only two electrical wires connecting it to a host apparatus. This sensing means can directly replace a magnetic reed switch or a mechanical switch having two contacts and connecting wires.
Another benefit of the invention is the ability to compensate for environmental changes such as signal drift and erroneous ‘stuck sensor’ conditions.
Yet another benefit of the invention is that it provides a small, inexpensive “beeper” switch having an audible output responsive to a user's touch and taking up no more room than a conventional silent switch.
Although it is believed that the foregoing recital of features and advantages may be of use to one who is skilled in the art and who wishes to learn how to practice the invention, it will be recognized that the foregoing recital is not intended to list all of the features and advantages, Moreover, it may be noted that various embodiments of the invention may provide various combinations of the hereinbefore recited features and advantages of the invention, and that less than all of the recited features and advantages may be provided by some embodiments.
REFERENCES:
patent: 3886447 (1975-05-01), Tanaka
patent: 4054833 (1977-10-01), Briefer
patent: 4806846 (1989-02-01), Kerber
patent: 4977480 (1990-12-01), Nishihara
patent: 5329239 (1994-07-01), Kindermann et al.
patent: 5343157 (1994-08-01), Deschamps
patent: 5537054 (1996-07-01), Suzuki et al.
patent: 5705807 (1998-01-01), Throngnumchai et al.
patent: 5726581 (1998-03-01), Vranish
patent: 5730165 (1998-03-01), Philipp
patent: 6188228 (2001-02-01), Philipp
patent: 6242927 (2001-06-01), Adams et al.
patent: 6278283 (2001-08-01), Tsugai
“Capacitive Sensors and Sensing Theory,” Product Catalog, Gordon Products, Inc., Brookfield, CT, USA, Oct. 1997.
Kiewit David
Sundaram T. R.
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