Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
2002-04-15
2003-11-04
Wu, Daniel J. (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S426110, C340S429000, C340S683000, C073S649000, C073S651000, C073S652000, C073S514250, C073S653000
Reexamination Certificate
active
06642848
ABSTRACT:
FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable,
MICROFICHE APPENDIX
FIELD OF INVENTION
The present invention relates to a shock sensor made of variable capacitors connected in series, used in door alarm, auto alarm, hard disk drive shock sensing devices, and automobile impact detector.
BACKGROUND OF THE INVENTION
Conventional shock sensors utilize a Piezo sensor or a Reed Switch to detect a shock experienced by an object. In a Piezo sensing system, in general, the sensitivity is poor because their sensed output is very low. It is necessary to have additional amplifying and control circuits. The structure of the product is complicated and their reliability is very poor.
In a Reed switch system, a magnetic device is used to activate and deactivate the switch depending upon the physical location of the magnet controlled by the extent of the shock given by the object. It is also difficult to adjust the sensitivity properly. Closing and opening the contact of a switch for a long period would cause the contact corrosive.
In a prior art, a shock sensor is made of a magnet, an inductor, a magnetically soft material, and a support bracket, and external circuit to amplify the electromagnetically induced voltage by the coil. To obtain the proper level of output voltage, for a product of the invention, the design process would not be easy. With those various parts, it may be too costly for a shock sensor of an automobile alarm system.
In another prior art, a pendulum and ring-assembly are used as a vibration responsive switch, which provides the circuit closure to activate an alarm. For this system, initially relatively heavy current is flowing through the contact of ring and pendulum switch because a gate current of a SCR system is flowing through the switch. This makes the ring and pendulum contact surface corrosive and will eventually reach to the point where the result is unsatisfactory. During initial assembly process, the positioning of the ring and pendulum may be difficult for a better sensitivity of the shock sensor.
SUMMARY OF THE INVENTION
In consideration of the aforementioned drawbacks and deficiencies of a shock sensor, the present invention endeavors to provide a reliable, simple, durable, and economical shock sensor with the wide range of application. As a first choice, this invention uses three conductive plates to comprise two capacitors connected in series. Two outer plates are firmly attached to a plastic support means which is an insulating material, and the center plate is arranged as movable within the two outer plates and connected to said plastic support means through a resilient part. The center plate is located at the middle of the distance between the two outer plates. The capacitance values of the two capacitors are the same provided that the outer plates are identical in shape, area, thickness, and material. When the two capacitors are connected to a DC voltage source in series with a resistor, each capacitor is charged to a one half of the applied voltage under the stand still. If the center plate is tilted toward an outer plate due to a shock, the capacitance values of the both capacitor would change in such a way that the smaller the distance between the plates is, the larger the capacitance, and vice versa. With the fixed supply voltage, the voltage charge across each capacitor is inversely proportional to the capacitance value. For an example, if the center plate is tilted toward the lower plate, the lower capacitance value is increased and the upper capacitance values is decreased, and the voltage charge across the lower capacitor is decreased and the voltage charge across the upper capacitor is increased. The changed value across one of the capacitor can be used at the next electronic circuit to process it and activate a desired object. As a second choice, this invention may use 2 conductive plates to comprise one capacitor where only 2 wires are available to be connected. If an external capacitor purchased from a store with an appropriate value is connected in series with the single capacitor of this invention, the same result would be obtained. However, 2 capacitors cascaded arrangement is preferable because the voltage change across a capacitor would be greater for a given extent of shock than a single capacitor connected with another fixed external capacitor in series. The tip of the movable plate (center plate) may be longer or wider or thicker than the outer plates to provide more weight for facilitating movement of the plate. Two coil springs can be used, one at each side of the center plate for more precision sensitivity. Not like a Piezo sensor which generates very minute sensor output, the present invention produces an apparent sensor output. Unlike a Reed switch method which checks only whether the switch is closed or open, the present invention can respond to any value of change. It is very simple to make and use a product of this invention and is very economical to produce a product of the present invention.
REFERENCES:
patent: 2916279 (1959-12-01), Stanton
patent: 5095752 (1992-03-01), Suzuki et al.
patent: 5719336 (1998-02-01), Ando et al.
patent: 6196067 (2001-03-01), Martin et al.
patent: 6422077 (2002-07-01), Krauss et al.
Nguyen Tai T.
Wu Daniel J.
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