US3531792A

US3531792A - Alarm system using saturable contacts

Info

Publication number: US3531792A
Application number: US599585A
Authority: US
Inventors: Samuel M Bagno; Peter M Joyce
Original assignee: Individual
Current assignee: Individual
Priority date: 1966-12-06
Filing date: 1966-12-06
Publication date: 1970-09-29
Anticipated expiration: 1987-09-29

Description

Sept. 29, 1970 s. M. BAGNO E 3,531,792

ALARM SYSTEM usme S-ATURABLE CONTACTS Filed D80. 6, 1966 2 Sheets-Sheet 1 y. 'EXTORS SAMUEL M. BAGNO PETER M. JOYCE ATfORNEYS Sept. 29, 1970 s. M. BAGNO mu. 3,531,792

ALARM SYSTEM USING SATURABLE CONTACTS Filed Dec. 6, 1966 FIG.2

Z SheetS-Sheet 2 S will N no finmlmmhilgi-F/ 1e 1\\'1:.\*10Rs SAMUEL M. BAGNO PETER M. JOYCE I Af'ronnsvs United States Patent ALARM SYSTEM USING SATURABLE CONTACTS Samuel M. Bagno, 18 Columbus Ave., Belleville, NJ.

07109, and Peter M. Joyce, Pacifica, Califi; said Joyce assignor to said Baguo Filed Dec. 6, 1966, Ser. No. 599,585 Int. Cl. G081) 13/08; H0112 21/00; H03k 17/80 U.S. Cl. 340-274 8 Claims ABSTRACT OF THE DISCLOSURE The alarm system has the usual continuity circuit including contacts on doors and/or windows, but the continuity circuit is supplied with alternating current, and the contacts are low impedance coils having high permeability cores each normally saturated by a permanent magnet which is separated from the core when the door or window is opened, thereby making the impedance so high as to act much like an open contact.

BACKGROUND OF THE INVENTION In a conventional alarm system there is a contact at each window and door, and a metal plated or foil ring or grid on glass panes, these being in series with the contacts, so that either breaking a pane or opening a closure will open the DC continuity circuit and cause an alarm. The usual contact is an ordinary mechancial contact and causes difficulty because of dust or dirt getting into it. To help prevent this the contacts sometimes are hermetically sealed, but then the contacts when closed may Stick, and are not accessible to be reopened. The protective alarm company works on a rental basis and provides free service, and the frequent service calls caused by contact trouble become costly. In many cases it is difficult to locate a break or a short in the DC continuity system.

SUMMARY OF THE INVENTION The present system uses alternating current and a saturable contact rather than a mechanical contact. The saturable contact comprises a coil having a closed core made of a high permeability material, and a permanent magnet is relatively movable toward or away from the core. When it is adjacent the core it serves to saturate the same, so that the impedance of the coil is very low, but when the core and magnet are separated the impedance is very high. The low impedance corresponds to a closed contact and the high impedance corresponds to an open contact. The magnet and the coil are secured to the openable closure and its frame in such relation that they are immediately adjacent when the closure is closed, and are separated when the closure is open. The alternating current has a frequency range of from about 1 to kilohertz (kilocycles per second). The alarm circuit preferably uses a silicon controlled rectifier acting as a locking relay switch, between a battery and the alarm device, and there is a detector means to rectify the AC in the continuity circuit to provide a negative voltage on the gate of the silicon controlled rectifier. The circuitry is such that a change from low to high impedance at the saturable contact results in a positive instead of a nega tive voltage on the gate of the silicon controlled rectifier, thereby sounding the alarm device.

The foregoing features and additional features of the invention are described in the following detailed specification, which is accompanied by drawings in which:

FIG. 1 is an electrical diagram showing an alarm system embodying features of the invention;

FIG. 2 is an elevation of a saturable contact. forming a part of the invention;

3,531,792 Patented Sept. 29, 1970 FIG. 3 is a bottom plan view of the same;

FIG. 4 is a perspective view showing a modification;

FIG. 5 shows a contact applied to a door;

FIG. 6 shows the contact in housings; and

FIG. 7 is a perspective view showing inductive and capacitive pickups which facilitate servicing the alarm system to readily locate a break or a short.

Referring to the drawing, and more particularly to FIGS. 2 and 3, the saturable contact comprises a coil 12 which may have the two additive windings shown in FIG. 3, these being wound on a core 14 which is made of a high permeability material such as Permalloy or high permeability ferrite. The core is preferably a closed core, and for convenience may be provided with soft iron ends or pole pieces 16. There is also a permanent magnet 18 which may be an Alnico or a ferrite permanent magnet. The magnet 18 is relatively movable toward or away from the core, and when it is adjacent the pole pieces 16, it serves to saturate the core 14, thereby making the impedance of the coil 12 very low. However, when the magnet 18 is separated from the core 14 the impedance of coil 12 is very high and corresponds in effect to an open circuit for alternating current.

The coil 12 may have say 1000 turns and a DC resistance which is only a matter of say 20 ohms. When the core is saturated the action is much as though the core were in air, and the impedance for AC is increased only slightly to a matter of, say, 50 ohms. However, when the permanent magnet is removed so that the high permeability of the core comes into effect, the inductive impedance is multiplied say a thousand times and may be a matter of say 25,000 ohms. This enormous change in inductance is utilized in the alarm circuitry.

A modified form of saturable contact is shown in perspective in FIG. 4. In this case the permanent magnet '50 is U-shaped, with its poles at the spacing of the soft iron pole pieces 52. The ferrite or other high permeability core having a low saturation flux density (say 4000 gauss) again is made of two E-shaped pieces 54 which are brought together, but in this case with the center arms inside a single coil 56'. It will be evident that this device will experience a very high change in impedance, the same as that previously described for the device shown in FIGS. 2 and 3.

It will be understood that the permanent magnet is mounted on a movable closure (or its fixed frame), and the coil is mounted on the fixed frame (or the closure), the relation of the parts being such that the magnet is adjacent the core when the closure is closed, and is moved away from the core when the closure is open.

Thus, referring to FIG. 5 the permanent magnet 60 of a saturable contact is shown mounted at the upper edge of a hinged door 62, while the coil 64 is fixedly mounted on the door frame or wall immediately above the magnet 60. When the door is opened the magnet is moved away from the saturable impedance, and when the door is closed it is moved to a position immediately adjacent the same.

In practice the magnet and coil may be in housings, as shown in FIG. 6. These may serve for protection, ease in mounting, and improved appearance.

Referring now to FIG. 1, it will be understood that a saturable contact, schematically represented at 12, may be connected in series with a metal plated or foil grid suggested at 20. Moreover, many windows and doors may be connected in series with one another, as is here indicated by the additional grid 22 and contact 24, and the grid 26 and contact 28.

The system consists of five basic sub-units, these being the oscillator, the continuity foils and saturable contacts, the detector, the alarm circuit, and the pick ups for continuity check.

The oscillator is a basic Hartley circuit centering about a transistor TR1. The tuned circuit is in the collector of transistor TR1, and consists of capacitor C3 and the winding c-d of a coupled inductor L1. The air gap at L1 is adjusted, to obtain a frequency of say 3 kHz. (kilohertz or kilocycles per second). The feedback is obtained through the winding 11-]; of inductor L1, and is fed into the emitter of transistor TR1 through a resistor R3, which serves to stabilize the collector current. The grounded base configuration of the transistor is maintained by a capacitor C1. Resistors R1 and R2 are biasing resistors for transistor TR1.

The output of the oscillator is taken through a coupling capacitor C2, and passes through the

various foils

20, 22, 26 and

contacts

12, 24, 28, the latter being saturable coils acting as Variable inductance switches as already described.

Each coil is wound on a core of high permeability, with a closed magnetic path which makes the inductance of the coil dependent entirely on the permeability of the core. The elfective permeability of the core is controlled by an external permanent magnet (not shown in FIG. 1) which saturates the core. The flux density caused by this magnet is so high that the core is saturated, which results in a very low effective permeability. The impedance, therefore, is very low.

When the magnet is removed, as by opening a door or window, the flux density goes down and the resulting high permeability causes a very high impedance to the 3 kHz. alternating current.

The detector comprises diodes D1 and D2, acting as a half wave voltage doubler. Diode D1 builds a voltage on a capacitor C4, and diode D2 supplies voltage to a capacitor C5.

The 3 kHz. signal from the contacts is decoupled by capacitor C4 from any DC potential which the circuit may have picked up, and is fed to diodes D1 and D2. The output of diode D2 is a negative voltage directly related to the amplitude of the 3 kHz. signal at the input to the detector. The detector voltage is smoothed by capacitor C5 and resistor R5 acting as a filter.

The alarm 30, typically a bell, is connected between a DC supply source, usually a six-volt storage battery 31, and ground, via a silicon controlled rectifier SCR1, acting as a locking relay switch for the bell. The gate of the silicon controlled rectifier is maintained at a negative potential as long as the output of the detector is sufficiently negative, by means of a voltage divider made up of resistor R4, diode D3, resistor R5, and diodes D2 and 2 D1. Diode D3 acts as a voltage limiter.

When the signal reaching the detector is suddenly reduced in amplitude, as is the case When a saturable contact opens, the voltage at the SCR gate becomes more 7 It may be noted that the voltage is applied to the gate of the silicon controlled rectifier through a high resistor R6. The same negative voltage, if it were reapplied with a high current available, that is, coming from a low impedance source, would make SCRl non-conductive and would stop the alarm, but here there is a high impedance R6 and a small current, and, therefore, SCRI remains conductive and the alarm stays on. At the outset of the operation the presence of the high impedance R6 is of no consequence because SCRl starts out in a non-conducting state to begin with. The reset button 32 makes SCRI non-conducting despite the resistor R6.

The capacitor C6 is provided to maintain a positive voltage across the silicon controlled rectifier in the intervals when the bell is an open circuit, the bell being for example a Wagner DC operated bell of the hammer type. The capacitor C6 around the bell maintains a positive voltage on SCRl during the repeated instants when the bell contacts are open as the bell vibrates.

One important advantage of the present system is in facilitating rapid servicing. All that is needed is an electrostatic pickup suggested at 34 in FIG. 7, and this may be a small metal plate, as shown, or even a simple short piece of wire. There is also an inductive pickup as shown at 36 in FIG. 7. Either may be connected to a very simple, compact single-stage transistor amplifier located in handle 38, which amplifier supplies earphones 40. A switch 42 connects either pickup 34 or 36 to the amplifier. The 3 kHz. frequency of the system is a tone frequency which is readily heard in the earphones. The electrostatic pickup may be used until one does not hear a tone, which indicates either that there is a short circuit, or that one is beyond a break in the circuit. If it is a break, one can locate the same by backing up to where the tone again is heard. If it is a short circuit, the inductive pickup serves best, and one may simply follow the tone to the point where the tone stops, and so the short circuit is located.

Some typical component values may be given as applied to the circuitry shown in FIG. 1, but these are given merely for illustration and are not intended to be in limitation of the invention.

The resistor: Value (ohms) R1 18K R2 2.2K

R4 47K R5 10K R6 27K The capacitor: Value tf.) C1 0.0047 C2 0.02 C3 0.0047 C4 0.02

In the coupling inductor L1 the coil a-b has turns and the coil c-d has 1000 turns. The coils of the saturable contacts have 1000 turns and a DC resistance of 20 ohms.

The diodes D1 and D2 are germanium diodes, such as type IN27 and the diode D3 is a silicon diode Solotron type HCV. The transistor is a Texas Instruments Type 2N1302. The silicon controlled rectifier is a General Electric Company Type C106B2.

The frequency used is high enough to permit the use of small coils, and also is convenient as a tone frequency.

The main advantage of the present system is in avoiding trouble with mechanical contacts. A further advantage is in readily and rapidly servicing the system to locate a break or a short. Still another advantage concerns the grids commonly electroplated on panes of glass. If different metals are used, during a rainstorm a counter potential may be generated which is bad for a DC system, but there is no eifect on the present AC system.

It is believed that the construction and method of use of our improved alarm system, as well as the advantages thereof, will be apparent from the foregoing detailed description.

We claim:

1. In a saturable contact for an alarm system of the type adapted for detecting movement of a closure such as a door or window or the like relative to the frame of said closure, a core made of a high permeability material and adapted for mounting on said frame, a coil wound on said core, and a permanent magnet adapted for mounting on said closure in such manner that said magnet and said core are adjacent when said closure is closed and are separated when said closure is open, said magnet serving to saturate said core when said magnet and core are adjacent, whereby the impedance of said coil to an audio frequency signal is low when said core and magnet are adjacent and is high when said core and magnet are separated.

2. A saturable contact as defined in claim 1, in which the core of the coil is a closed core.

3. A saturable contact as defined in claim 1, together with means connecting said contact into the continuity circuit of an alarm system and means for supplying said continuity circuit with alternating current having a frequency in the audio frequency range.

4. A saturable contact as defined in claim 3, in which the closure has glass fitted with a continuity foil, and in which the contact is connected electrically in series with said continuity foil.

5. In a burglar alarm system, a continuity circuit and an alarm circuit connected thereto and controlled thereby, said continuity circuit including one or more saturable contacts as defined in claim 1 and being supplied with alternating current at an audio frequency, and said alarm circuit comprising a battery, an alarm device, a silicon controlled rectifier connected as a normally open locking relay switch between said battery and said alarm device, means to rectify the alternating current in the continuity circuit to provide a negative voltage on the gate of the silicon controlled rectifier, the circuitry being such that a change from low to high impedance at the saturable contact produces a positive voltage on the gate of the silicon controlled rectifier, thereby triggering said silicon controlled rectifier and energizing said alarm device until said silicon controlled rectifier is again made non-conductive by suitable reset means.

6. In a burglar alarm system, a continuity circuit and an alarm circuit connected to said continuity circuit and controlled thereby, said continuity circuit including one or more serially connected saturable contacts and continuity foils, each of said saturable contacts including a magnet mounted on a closure and a permeable core having a coil wound thereon mounted on the frame of said closure in such manner that said magnet and core are adjacent when said closure is closed and separated when said closure is open, and said alarm circuit comprising a direct current source, an alarm device, normally open electronic switch means connected between said direct current source and said alarm device, and means connecting said continuity circuit to the control element of said electronic switch means in such manner that an increase in the impedance of said saturable contacts triggers said electronic switch means, thereby connecting said alarm device to said direct current source and energizing said alarm device until said electronic switch means is again made non-conductive by suitable reset means.

7. A saturable contact as defined in claim 6, together with means connected to said continuity circuit for supplying said circuit with alternating current having a fre quency on the order of 1 kilohertz to 5 kilohertz.

8. A saturable contact as defined in claim 6, in which the closure includes glass fitted with a continuity foil, and in which said saturable contact is connected electrically in series with said continuity foil.

References Cited UNITED STATES PATENTS 3,018,456 1/1962 White 336 3,070,739 12/1962 Hansen et a1. 307-252X 3,284,787 11/1966 Voigt et a1. 307252X FOREIGN PATENTS 612,820 1/1961 Canada.

DONALD J. YUSKO, Primary Examiner 5 P. PALAN, Assistant Examiner US. Cl. X.R.