US3571666A

US3571666A - Double-action capacitance-responsive switching circuit

Info

Publication number: US3571666A
Application number: US720889A
Authority: US
Inventors: Francis A Mcguirk Jr
Original assignee: Wagner Electric Corp
Current assignee: Cooper Industries LLC
Priority date: 1968-04-12
Filing date: 1968-04-12
Publication date: 1971-03-23
Anticipated expiration: 1988-03-23

Abstract

The variations in capacitance to ground of an antenna due to proximity or remoteness of a person or object causes variations in the output of an oscillator. In one embodiment, when antenna capacitance either increases or decreases with respect to a predetermined level, the oscillator output decreases or increases (respectively) and thereby causes switching circuitry to energize or deenergize (respectively) both of two relays, thus causing energization of a load. At the normal antenna capacitance, one relay is energized and the other is deenergized, and the load is deenergized. In a second embodiment, the same load-controlling functions are achieved with a circuit employing a single relay.

Description

United States Patent [72] lnventor Francis A. McGuirk,Jr.

Chatham, NJ. [21] Appl. No. 720,889 [22] Filed Apr. 12,1968 [45] Patented Mar. 23,1971 [73] Assignee Wagner Electric Corporation [54] DOUBLE-ACTION CAPACITANCE-RESPONSIVE SWITCHING CIRCUIT 9 Claims, 4 Drawing Figs.

[52] U.S.C1 317/146, 317/148.5, 340/258 [51] Int. Cl ..H01h 47/22 [50] Field ofSearch 317/135, 136, 139, 140.5, 146, 148.5, 149 (originals), 137; 340/258 (C) [5 6] References Cited UNITED STATES PATENTS 2,704,339 3/1955 Wescott, Jr. et a1. 317/146 2,137,349 11/1938 Rezos 340/253 3,255,380 6/1966 Atkins et a1... 340/258 3,436,607 4/1969 Yagusic 317/142 Primary Examiner- William M. Shoop, Jr. Assistant Examiner-Harry E. Moose, Jr. Att0rneyEyre, Mann & Lucas ABSTRACT: The variations in capacitance to ground of an antenna due to proximity or remoteness of a person or object causes variations in the output of an oscillator. In one embodiment, when antenna capacitance either increases or decreases with respect to a predetermined level, the oscillator output decreases or increases (respectively) and thereby causes switching circuitry to energize or deenergize (respectively) both of two relays, thus causing energization of a load. At the normal antenna capacitance, one relay is energized and the other is deenergized, and the load is deenergized. In a second embodiment, the same load-controlling functions are achieved with a circuit employing a single relay.

IDGUlBlLlE-ACTHON CAPACITANCE-RESPGNSHVE SWITCHING CIRCUIT This invention relates to a circuit coupled to a small capacity formed by electrodes attached to objects which are to be protected from unlawful movement. The circuit operates a relay and sounds an alarm when a person approaches too close to the object to be protected. The circuit also operates to sound an alarm if the protected object is removed from its position by a nonconductive rod and the capacity is reduced instead of increased.

Many types of burglar alarms have been developed and tried. So far, none of the prior-art devices are free from tampering. Wires can be cut, short circuited, or otherwise manipulated so that the alarm is deactivated. The present invention uses the capacity between a conductive layer on or in the object and a conductive layer positioned behind a support on which the object rests. Since both conductive layers can be positioned under other layers, it is impossible to manipulate connections to cause the alarm system to be deactivated. Other systems have been developed to sense the increase of a capacity and to operate loads when this capacity exceeds a predetermined value. The present invention operates a load (alarm) when the capacity is either increased or decreased.

For a better understanding of the invention, reference should be made to the drawings, of which:

FIG. 1 is a side view, partly in section, of a picture hanging on a wall, showing two capacitor plates which form the means for controlling the circuit;

FIG. 2 is a side view, partly in section, of a support for a vase, showing similar capacitor plates;

FIG. 3 is a schematic diagram of connections of one sensing circuit wherein two semiconductor switches are connected in parallel; and

FlG. 4 is a schematic diagram of connections of an alternate sensing circuit wherein two semiconductor switches are connected in series.

Referring now to FIG. 1, a wall is shown supporting a picture 11 provided with a conductive layer 12, which may be a thin piece of foil secured to the back of the frame. The layer 12 is connected to a metal wire 13 which is supported by a nail or other fixture and the nail is connected to a conductor 14 which leads to the alarm circuit. A second conductive film 15 is secured to the other side of the wall out of reach of people viewing the picture. The film 15 is connected to a conductor 16 which leads to another portion of the alarm circuit. Film 15 may be positioned within the wall 11) if desired.

A person 17, indicated in dotted lines, is shown standing in front of the picture 11, too close for proper viewing and in a position where one could lift the picture from its support. It is obvious that the added capacity, formed by the person, is sufficient to raise the capacity between

conductors

14 and 16 by a considerable amount. This added capacity is one of the signals which trigger the alarm.

FIG. 2 shows a vase 18 on exhibit, supported by a box 20 which is made of nonconductive material. The bottom of the vase is coated with a conductive film 12 and contact with this film is made to conductor 14. Inside the box 20 is a conductive plate 15, connected to conductor 16. The presence of a person close to the vase increases the capacity of

plates

12 and 15 and sets oh the alarm. As soon as the vase is lifted, connection to conductor 14 is broken and the decrease in capacity again sets off the alarm.

The circuit diagram shown in FIG. 3 is the preferred circuit for employing the change in capacity to vary the input signals to two semiconductor switches and thereby sound an alarm. The circuit includes a pair of

terminals

21, 22, which are to be connected to a source of alternating current power. Coupled to the

capacitor plates

12, 15 is a relaxation oscillator having a neon lamp 23 as the nonlinear component. The oscillator circuit also includes a chargeable capacitor 24, a series resistor 25, and a voltage-dividing resistor 26.

The operation of this oscillator is well known and has been described in many publications. During each half cycle of the applied power, current through resistance charges capacitor 24 until the breakdown potential of the neon discharge tube 23 is reached. Then current passes through the tube 23,

discharging the capacitor, and generating a pulse which is a9 plied to resistor 26. At the same time, the capacitor formed by plates 12, i5 is charged and discharged thereby producing two opposite currents in the two halves of resistor 26. The sliding contact on resistor 26 can be adjusted so that the currents create potential differences at the ends of resistor 26 which cancel each other. However, in the preferred embodiments of the present invention, this circuit is adjusted so that each positive half cycle of the power supply results in a small positive pulse at the high side of resistor 26.

Resistor 26 is connected across the input terminals of the first stage of a two-stage amplifier, the first stage including a transistor 27 having its emitter and collector electrodes connected across the alternating

current supply lines

28 and 30 in series with a resistor 31. Resistor 29 is connected between the base and the collector of transistor 27 to provide the bias voltage across the base-collector junction. This stage amplifies pulses received from the oscillator during the positive half cycle of the applied AC power. The amplified pulses are applied through a blocking capacitor 32 to the base electrode of a second transistor 33. The second stage is similar to the first and amplifies only the pulses received during the positive halves of the applied AC power. A stabilizing voltage

divider including resistors

34 and 35 has its midpoint connected to the collector of transistor 33 while the load resistor 36 is connected between the emitter and the conductor 30. Resistor 37 is connected between the base and the collector of transistor 27 to provide the bias voltage across the base-collector function. Coupling capacitors 38 transfer the signal pulses to two

semiconductor switches

40 and 41.

Switch 40 is a complementary transistor pair consisting of PNP transistor 42 and an NPN transistor 43. The transistors are connected in a regenerative feedback configuration with the base of transistor 42 connected to the collector electrode of transistor 43. When a positive half wave is applied across the two emitters, the combination is nonconductive unless the base of transistor 43 is raised above a threshold voltage of about 10 volts. When this voltage is exceeded, the combination is made conductive and current passes from conductor 28 to conductor 30, limited only by the series resistance 44.

Switch 41 is also a complementary transistor pair consisting of

transistors

45 and 46 connected in a regenerative feedback configuration. When a positive half wave is applied across the two emitters, the combination is nonconductive unless the base of transistor 45 is raised above a threshold voltage of about 6 volts. When this voltage is exceeded, the combination is made conductive and current passes from conductor'28 to conductor 30, limited only by the series resistor 47.

Switch 40 is bridged across a relay winding 48 in series with a diode 50. In a similar manner switch 41 is bridged across a relay winding 51 in series with another diode 52. Diodes and 52 prevent negative AC pulses from passing through the windings. Both windings are respectively shunted by capacitors 53 and 54 to absorb the alternating components of the signal and to eliminate chattering of the

armatures

55 and 56. Relay winding 48 operates armature 55 to open a pair of contacts 57 and close another pair of contacts 58 whenever current is applied to the winding. In a similar manner winding 51 operates armature 56 to open contacts 60 and close contacts 61 whenever winding 53 receives current. Contacts 57 are connected by conductor 62 to contacts 66 and contacts 58 are connected by conductor 63 to contacts 61. Armature 55 is connected to AC terminal 21 while armature 56 is connected to a load 64 which may be an alarm or some indicating means. The other load terminal is connected to the other AC terminal 22. The relay contacts and conductors 62 and 63 are connected so that the load 64 receives current whenever both relays are actuated or when both relays are unactuated. When either one is actuated and the other is unactuated, the load 64 is not energized.

When the circuit shown in FIG. 3 is put in operation, the sliding contact on resistor 26 is adjusted so that the pulse amplitudes applied through capacitors 38 are about 8 volts. Under these conditions semiconductor switch 41 is made conductive and switch 40 remains nonconductive. Switch 41 short circuits winding 51 and armature 56 is not moved. Switch 40 is nonconductive and positive current pulses flow through diode 50 and winding 48 to operate the armature 55, open contacts 57, close contacts 58, and cut off current from the load. This is the normal mode of operation when the capacity between

plates

12 and 15 is the predetermined normal value.

Now, if a person 17 approaches too close to the painting, the capacity of

plates

12, 15 is increased and the current through the lower part of resistor 26 is increased, thereby lowering the amplitude of the positive pulses applied to transistor 27 and to switch 41. This change causes switch 41 to be nonconducting and positive pulses are then sent through relay winding 51 to operate its armature 56 and send current through the load, sounding an alarm. If an unauthorized person stands at a distance and lifts the picture from its support by means of a nonconducting hook, the capacity between

plates

12 and 15 is lowered and the current through the lower portion of resistance 26 is reduced, thereby increasing the amplitude of the positive pulses applied to transistor 27 and to switch 40. As soon as the amplitude of the pulses is greater than volts, both

switches

40 and 41 conduct. This action normalizes both relays and current is again sent through contacts 57 and 60 to the load, sounding the alarm.

A preferred set of values for the components of the circuit shown in FIG. 3 is as follows:

Neon Lamp 23 Breakdown: 100 l 20 volts Maintain: 6070 volts Capacitor 24 50 picofarads Resistor 25 1.8 megohms Resistor 26 19,700 ohms (maximum) Transistor 27 2N3 567 Resistor 29 330,000 ohms Resistor 31 220,000 ohms Capacitor 32 0.01 microfarads Transistor 33 2N35 67 Resistor 34 47,000 ohms Resistor 35 15,000 ohms Resistor 36 18,000 ohms Resistor 37 1.5 megohms Capacitor 38 120 picofarads Transistor 42 2N3638 Transistor 43 SE 1 001 Resistor 44 8200 ohms Transistor 45 2N3567 Transistor 46 2N363 8 Resistor 47 8200 Capacitor 53 l5 microfarads Capacitor 54 microfarads Resistor 83 3 3,000 ohms Capacitor 84 0.01 microfarads The circuit shown in FIG. 4 includes the same capacitor connections, the same relaxation oscillator, and two similar stages of amplification with

transistors

27 and 33 and their associated bias circuitry. As before, pulses applied through blocking capacitor 38 operate to make semiconductor switch 40 conductive or nonconductive in accordance with the condition of the capacitor formed by

plates

12 and 15. However, this circuit differs from the circuit of FIG. 3 by the addition of a third amplifier stage including a transistor 59, coupled to the collector electrode of transistor 27 by a blocking capacitor 69. Also, the emitter of transistor 42 is connected to a blocking capacitor 71. Transistor 59 has a bias resistor 65 connected between its base and collector, a resistor 66 between its emitter and conductor 30. Voltage-dividing resistors 67 and 68 are bridged across the

AC supply lines

28, 30 and their junction is connected to the emitter of transistor 59. The base electrode of transistor 59 is coupled to the collector of transistor 27 by a blocking capacitor 69 so that the amplifier

stages including transistors

33 and 59 are in parallel array.

A second semiconductor switch 70 is coupled to the emitter electrode of transistor 59 by the blocking capacitor 71. Switch 70 is similar to

switches

40 and 41, and includes transistors 72 and 73. As in the other switches, the base of each transistor is connected to the collector of the other transistor. The emitter electrodes of switch 70 are connected across the

AC supply line

28, 30 in series with a limiting resistor 74.

A single relay is all that is necessary to couple this circuit to a load 75. The relay includes a winding 76 having one end connected to the emitter of transistor 72 in series with a diode 77 and the end connected to the AC supply line 30. As before, the winding 76 is shunted by a capacitor 78 to eliminate most of the AC portions of the rectified current. Winding 76 operates an armature 80 to close a pair of contacts 81 in series with the load and the

AC supply terminals

21, 22.

The operation of this circuit (FIG. 4) is as follows: When there is a normal input capacity sensed between

plates

12 and 15, the positive pulses sent through capacitor 37 are about 8 volts. Switch 40 remains nonconductive and has no influence on switch 70. Switch 70 is made conductive by the 8 volt positive pulses sent through transistor 59 and capacitor 71 and, because of this conductive circuit, relay winding 76 is short circuited, receiving no current, and the load circuit 75 remains unactuated. If a person approaches too close to the painting or the vase, the capacity of plates l2, 15 is increased, the positive pulses applied to

switches

40 and 70 are less than 6 volts, and both switches are made nonconductive. Relay winding 76 receives current, armature is actuated, and load 75 receives current sounding an alarm.

If the painting or vase is removed from its normal position the capacity of

plates

12, 15 is reduced considerably and the current through the lower portion of resistor 26 is lowered. This results in a series of positive pulses, applied through capacitor 37, which are greater than 10 volts and switch 40 is made conductive, short circuiting resistor 66, and thereby greatly decreasing the signal applied through capacitor 71 to switch 70. Switch 70 is thus made nonconductive, current passes through diode 77 and relay winding 76 to operate the armature 80 and energize the load 75.

In the circuit diagrams of FIGS. 3 and 4,

transistors

43, 45, and 73 receive bias potentials for their base electrodes from a bias circuit which includes a resistor 83 and a capacitor 84 connected in series. This circuit maintains a negative bias of about 6 volts for transistors 45 and 73 and 10 volts for transistor 43 because of the zener breakdown voltages of the respective emitter-base junctions of these transistors. During the negative half cycles, current leaks through the PNP transistors 42, 46, and 72 to charge capacitor 84. As the voltage builds up on this capacitor, the zener breakdown voltage of NPN transistor 43 (or 45, 73) is reached and excess charging current is shunted to ground. This circuit is described in application Ser. No. 550,765, filed by Carl E. Atkins, May 17, 1966, abandoned in favor of continuation-in-part application Ser. No. 755,507 filed by Carl E. Atkins on Aug. 20, 1968, upon which US. Pat. No. 3,508,120 issued on Apr. 21, 1970.

A preferred set of values for the components of the circuit shown in FIG. 4 is as follows:

Neon Lamp 23 Breakdown: volts Maintain: 60-70 volts Capacitor 24 50 picofarads Resistor 25 2.2 megohms Resistor 26 21,700 ohms (maximum) Transistor 27 2N3 567 Resistor 29 330,000 ohms Resistor 31 220,000 ohms Capacitor 32 0.01 microfarads Transistor 33 2N3 567 Resistor 34 47,000 ohms Resistor 35 15,000 ohms Resistor 36 18,000 ohms Resistor 37 1.5 megohms Capacitor 38 0.001 microfarads Transistor 42 2N 3 63 8 Transistor 43 2N3 567 Transistor 59 2N3 567 Resistor 65 1.5 megohms Resistor 66 1 8,000 ohms Resistor 67 47,000 ohms Resistor 68 ,000 ohms Capacitor 69 0.01 microfarads Capacitor 71 0.001 microfarads Transistor 72 2N3638 Transistor 73 SE 1 001 Resistor 74 8200 ohms Capacitor 78 l5 microfarads Resistor 83 33,000 ohms Capacitor 84 0.05 microfarads The advantages of the present invention, as well as certain changes and modifications of the disclosed embodiments thereof, will be readily apparent to those skilled in the art. It is the applicant's intention to cover all those changes and modifications which could be made to the embodiments of the invention herein chosen for the purposes of the disclosure without departing from the spirit and scope of the invention.

1 claim:

1. A capacitance-responsive circuit comprising:

1. first and second power input terminals for connecting said circuit to a source of alternating current power;

2. signal-generating means including antenna means operative to vary the output of said signal-generating means in response to variations in capacitance detected by said antenna means;

3. first and second actuating current control means controlled by said signal-generating means and including first and second switching means, said first switching means having a higher turn-on threshold than said second switching means; and

4. at least one relay means controlled by said first and second actuating current control means and operative to open a load circuit when the capacitance detected by said antenna means is within a predetermined range of values, and further operative to close said load circuit when the capacitance detected by said antenna means is either above or below said predetermined range of values.

2. A capacitanceqesponsive circuit according to claim 1 wherein said first switching means controls the energization and deenergization of a first relay means and said second switching means controls the energization and deenergization of a second relay means, said load circuit being closed only when said first and second relays are either both energized or both deenergized.

3. A capacitance-responsive circuit according to claim 1 wherein said first and second switching means each comprises:

1. a complementary transistor pair connected in the regenerative feedback configuration; and

2. first and second bias circuit means operative to bias said first and second switching means, respectively, normally 7 nonconductive.

4. A capacitance-responsive circuit according to claim 1 wherein said first switching means is operative to reduce the signal applied to said second switching means below the turnon level of said second switching means when the signal applied to said first switching means is above the turn-on level of said first switching means.

5. A capacitance-controlled circuit according to claim 1 wherein said first switching means controls the input signal to said second switching means, and each of said switching means comprises:

2. first and second bias means operative to bias said first and second switching means, respectively, nonconductive.

6. A load-controlling circuit comprising:

1. first and second power input terminals;

2. first and second actuating current control circuit means including first and second switching means, respectively, said first switching means having a higher turn-on threshold than said second switching means; and 3. first and second relay means electrically connected to said first and second actuating current control circuits, respectively, and operative to control a load circuit connection to said input terminals, said first and second relay means each having first and second fixed contacts and an armature operative selectively to engage said first or said second contact, said first contacts being electrically connected to each other, said second contacts being electrically connected to each other, and said armature of said first relay means being electrically connected to said first power input terminal so that when a load is connected between said armature of said second relay means and said second power input terminal, the load circuit is closed only when said first and second relay means are either both energized or both deenergized.

. A load-controlling circuit according to claim 6 wherein:

. said first and second switching means each comprises a complementary transistor pair, each transistor having 2. said first and second actuating current control circuit means include first and second diodes, respectively, connected at their anodes to the emitters of the first transistors of said first and second transistor pairs, respectively, and at their cathodes to the windings of said first and second relay means, respectively; and

. first and second capacitance means connected in parallel with the windings of said first and second relay means, respectively.

8. A load-controlling circuit comprising:

2. first and second actuating current control circuit means including first and second switching means, respectively, said first switching means having a higher turn-on threshold than said second switching means, said first actuating current control circuit means being operative to shunt the input to said second switching means when said first switching means is conductive; and

3. relay means electrically connected to said second actuating current control circuit, said relay means being operative to close a load circuit through said power input terminals only when said power input terminals are connected to a source of alternating current power and said second switching means is nonconductive.

9. A load-controlling circuit according to claim 8 wherein said first and second actuating current control circuit means comprise first and second amplifying circuit means, respectively, connected to said first and second switching means, respectively, for providing input signals thereto;

2. said second switching means is coupled to said relay by a diode having its cathode connected to the winding of said relay; and

3. said relay winding is connected in parallel with a capacitor.

P0405 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,57 66 Dated March 23, 1971 Inventor(s) r iS A. MCGuirk, Jr.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

C01. t, Line 11: --other-- between "the" and "end" omitted.

Col. 6, Line 27 Claim 7 (1): --an emitter, a base, and a collector, said transistor pair being connected in the regenerative feedback configuration and having bias circuit means;-- omitted after "having" Signed and sealed this 22nd day,' of June l9Yl.

(SEAL) Attest:

EDWARD I-I.FLETCHER,JR.

Attesting Officer Commissioner of Patents WILLIAM 111. SCHUYLER, JR.

Claims

1. A capacitance-responsive circuit comprising: 1. first and second power input terminals for connecting said circuit to a source of alternating current power; 2. signal-generating means including antenna means operative to vary the output of said signal-generating means in response to variations in capacitance detected by said antenna means; 3. first and second actuating current control means controlled by said signal-generating means and including first and second switching means, said first switching means having a higher turn-on threshold than said second switching means; and 4. at least one relay means controlled by said first and second actuating current control means and operative to open a load circuit when the capacitance detected by said antenna means is within a predetermined range of values, and further operative to close said load circuit when the capacitance detected by said antenna means is either above or below said predetermined range of values.

2. A capacitance-responsive circuit according to claim 1 wherein said first switching means controls the energization and deenergization of a first relay means and said second switching means controls the energization and deenergization of a second relay means, said load circuit being closed only when said first and second relays are either both energized or both deenergized.

2. first and second bias circuit means operative to bias said first and second switching means, respectively, normally nonconductive.

2. first and second actuating current control circuit means including first and second switching means, respectively, said first switching means having a higher turn-on threshold than said second switching means; and

2. said first and second actuating current control circuit means include first and second diodes, respectively, connected at their anodes to the emitters of the first transistors of said first and second transistor pairs, respectively, and at their cathodes to the windings of said first and seconD relay means, respectively; and

3. said relay winding is connected in parallel with a capacitor.

3. first and second capacitance means connected in parallel with the windings of said first and second relay means, respectively.

3. first and second relay means electrically connected to said first and second actuating current control circuits, respectively, and operative to control a load circuit connection to said input terminals, said first and second relay means each having first and second fixed contacts and an armature operative selectively to engage said first or said second contact, said first contacts being electrically connected to each other, said second contacts being electrically connected to each other, and said armature of said first relay means being electrically connected to said first power input terminal so that when a load is connected between said armature of said second relay means and said second power input terminal, the load circuit is closed only when said first and second relay means are either both energized or both deenergized.

4. A capacitance-responsive circuit according to claim 1 wherein said first switching means is operative to reduce the signal applied to said second switching means below the turn-on level of said second switching means when the signal applied to said first switching means is above the turn-on level of said first switching means.

6. A load-controlling circuit comprising:

7. A load-controlling circuit according to claim 6 wherein:

8. A load-controlling circuit comprising:

9. A load-controlling circuit according to claim 8 wherein