US3697971A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Alarm system
Assignee: Individual
•
Filing: 1970-12-30
•
Granted: 1972-10-10
•
Expires: 1990-12-30
Abstract
Abstract A capacitive alarm system for detecting the presence of an intruder, including an oscillator, a level sensitive switch driven by the oscillator, an alarm controlled by the switch, and an antenna coupled to the oscillator. Changes in capacitance in the proximity of the antenna vary the level of the oscillator output and, in the presence of an intruder, trigger the switch and alarm. A negative feed-back network, including a lightsensitive variable resistor, is connected to the oscillator. The output of the oscillator also drives a lamp that illuminates the light-sensitive variable resistor. Slowly varying changes in capacitance, due to variations in temperature and humidity, vary the level of the oscillator output and the intensity of the light from the lamp. The variation in intensity of illumination from the lamp directly varies the resistance of the light-sensitive variable resistor so as to maintain the level of the oscillator output constant. The long-time constant of the lamp and the light-sensitive variable resistor circuit prevents compensation for the rapid variations in capacitance associated with the appearance of an intruder.
Inventors
- 👤 Siegfried Domin
- 👤 Roy Nembhard
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-28 11:16
CPC Classifications
G; G08; G08B; G08B13/00; G08B13/22; G08B13/26
Claims Analysis
Total Claims: 16
Claim 1
Independent Claim
205 words
A capacitive alarm system for detecting an intrusion into the proximity of the system, comprising: oscillator means having a range of self-resonant operating frequencies for producing an output signal, the level of said output signal being substantially constant within said operating range; antenna means coupled to the oscillator means for varying the level of the output signal in response to variations in capacitance between the antenna means and ground; a level sensitive switch having a normal and an alarm state, said switch being coupled to the oscillator means output and being responsive to variations of predetermined magnitudes in the level of the oscillator means output signal to change from said normal to said alarm state; an alarm coupled to the level sensitive switch and responsive to change in state of the level sensitive switch to produce an alarm signal; and feedback means coupled to the oscillator means and having a long time constant relative to variations in capacitance due to intrusion in the proximity of the antenna means for maintaining the level of the oscillator means output signal relatively constant over a wide range of slow variations in capacitance between the antenna means and ground, whereby variations in atmospheric conditions will not trigger said alarm.
Claim 2
Dependent Claim
205 words
A capacitive alarm system for detecting an intrusion into the proximity of the system, comprising: oscillator means having a range of self-resonant operating frequencies for producing an output signal, the level of said output signal being substantially constant within said operating range; antenna means coupled to the oscillator means for varying the level of the output signal in response to variations in capacitance between the antenna means and ground; a level sensitive switch having a normal and an alarm state, said switch being coupled to the oscillator means output and being responsive to variations of predetermined magnitudes in the level of the oscillator means output signal to change from said normal to said alarm state; an alarm coupled to the level sensitive switch and responsive to change in state of the level sensitive switch to produce an alarm signal; and feedback means coupled to the oscillator means and having a long time constant relative to variations in capacitance due to intrusion in the proximity of the antenna means for maintaining the level of the oscillator means output signal relatively constant over a wide range of slow variations in capacitance between the antenna means and ground, whereby variations in atmospheric conditions will not trigger said alarm.
Claim 3
Dependent Claim
51 words
The apparatus defined in claim 1 wherein the feedback means includes a negative feedback network in which the amount of feedback varies as a function of the level of the oscillator means output signal for slow variations in capacitance between the antenna means and ground due to variations in atmospheric conditions.
Claim 4
Dependent Claim
44 words
The apparatus defined in claim 2 wherein the negative feedback network includes a variable impedance element and wherein the feedback means includes conditioning means for varying the impedance of the variable impedance element in response to the level of the oscillator means output signal.
Claim 5
Dependent Claim
30 words
The apparatus of claim 3 wherein: the variable impedance element comprises a light sensitive variable resistor; and the conditioning means including a lamp positioned to illuminate the light-sensitive variable resistor.
Claim 6
Dependent Claim
73 words
The apparatus of claim 1 wherein: the oscillator means includes a linear amplifier having an input and an output, an operational amplifier having an input and an output and having its input coupled to the linear amplifier output and its output coupled to the oscillator means output, and a positive feedback network coupled between the linear amplifier input and the operational amplifier output; and the antenna is Coupled to the linear amplifier output.
Claim 7
Dependent Claim
55 words
The apparatus of claim 5 wherein the feedback means includes a negative feedback network coupled between the input and output of the operational amplifier for varying the amount of feedback responsive to the level of the oscillator means output signal for slow variations in capacitance between the antenna means and ground due to atmospheric variations.
Claim 8
Dependent Claim
176 words
In a capacitive alarm system the combination comprising: a first amplifier having an input and an output; a second amplifier having an input and output and having the input coupled to the first amplifier output; a positive feedback network coupled between the second amplifier output and the first amplifier input forming a frequency independent oscillator circuit with the output appearing at the second amplifier output; antenna means coupled to the first amplifier output for coupling changes in capacitance in the area proximate the antenna means to the first amplifier output; a wide range negative feedback network coupled between the input and output of the second amplifier and including a light-sensitive variable resistor coupled in series in the network; a lamp driver having an input and an output and having the input coupled to the output of the second amplifier; and a lamp coupled to the output of the lamp driver positioned to illuminate the light-sensitive variable resistor, and having the intensity proportional to the amplitude of the signal appearing at the output of the second amplifier.
Claim 9
Dependent Claim
176 words
In a capacitive alarm system the combination comprising: a first amplifier having an input and an output; a second amplifier having an input and output and having the input coupled to the first amplifier output; a positive feedback network coupled between the second amplifier output and the first amplifier input forming a frequency independent oscillator circuit with the output appearing at the second amplifier output; antenna means coupled to the first amplifier output for coupling changes in capacitance in the area proximate the antenna means to the first amplifier output; a wide range negative feedback network coupled between the input and output of the second amplifier and including a light-sensitive variable resistor coupled in series in the network; a lamp driver having an input and an output and having the input coupled to the output of the second amplifier; and a lamp coupled to the output of the lamp driver positioned to illuminate the light-sensitive variable resistor, and having the intensity proportional to the amplitude of the signal appearing at the output of the second amplifier.
Claim 10
Dependent Claim
20 words
The apparatus defined in claim 7 wherein the second amplifier and the negative feedback network form a differential operational amplifier.
Claim 11
Dependent Claim
50 words
The apparatus defined in claim 8 wherein the negative feedback network includes a second variable resistor connected in series with the light-sensitive variable resistor to permit adjustment of the gain of the second amplifier whereby various antenna means may be accommodated by varying the feedback of the differential operational amplifier.
Claim 12
Dependent Claim
14 words
The apparatus defined in claim 9 wherein the first amplifier is a linear amplifier.
Claim 13
Dependent Claim
37 words
The apparatus defined in claim 9 wherein the differential operational amplifier includes a third variable resistor connected in series with the input to permit adjustment of the gain of the operational amplifier to accommodate various antenna means.
Claim 14
Dependent Claim
178 words
A capacitive alarm system comprising: a first amplifier having an input and an output; a second amplifier having an input and an output and having its input coupled to the first amplifier output; a positive feedback network coupled between the second amplifier output and the first amplifier input forming a frequency independent oscillator circuit with the output appearing at the second amplifier output; antenna means coupled to the first amplifier output for coupling changes in capacitance in the area surrounding the antenna means to the first amplifier output; a wide range negative feedback network coupled between the input and output of the second amplifier and including a variable resistor for fine adjustment of the gain of the second amplifier; a level sensitive switch having an input and an output, its input connected to the output of the second amplifier, said switch being responsive to the level of the signal appearing at the output of the second amplifier to switch from a normal to an alarm state; and an alarm connected to the output of the level sensitive switch.
Claim 15
Dependent Claim
178 words
A capacitive alarm system comprising: a first amplifier having an input and an output; a second amplifier having an input and an output and having its input coupled to the first amplifier output; a positive feedback network coupled between the second amplifier output and the first amplifier input forming a frequency independent oscillator circuit with the output appearing at the second amplifier output; antenna means coupled to the first amplifier output for coupling changes in capacitance in the area surrounding the antenna means to the first amplifier output; a wide range negative feedback network coupled between the input and output of the second amplifier and including a variable resistor for fine adjustment of the gain of the second amplifier; a level sensitive switch having an input and an output, its input connected to the output of the second amplifier, said switch being responsive to the level of the signal appearing at the output of the second amplifier to switch from a normal to an alarm state; and an alarm connected to the output of the level sensitive switch.
Claim 16
Dependent Claim
50 words
The apparatus defined in claim 12 including a variable resistor connected in series with the input of the second amplifier to permit course adjustment of the gain of the second amplifier and thus the level of the signal appearing at the oscillator output, whereby various antenna means may be accommodated.
References Cited (Backward Citations)
US3225304A
Cited
US3461352A
Cited
US3483437A
Cited
US3504236A
Cited
US3462755A
Cited
US3379991A
Cited
US3575640A
Cited
US3571666A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1975-10-10 | 1976-04-10 | 1976-10-10 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-10-10 | 1980-04-10 | 1980-10-10 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-10-10 | 1984-04-10 | 1984-10-10 | $7700.00 | Window Closed / Lapsed |