US3161742A

US3161742A - Magnetic intruder and fire deterctor

Info

Publication number: US3161742A
Application number: US133714A
Authority: US
Inventors: Samuel M Bagno
Original assignee: Specialties Development Corp
Current assignee: Specialties Development Corp
Priority date: 1961-08-24
Filing date: 1961-08-24
Publication date: 1964-12-15
Anticipated expiration: 1981-12-15

Description

Dec. 15, 1964 s, BAGNO 3,161,742

MAGNETIC INTRUDER AND FIRE DETECTOR Filed Aug. 24, 1961 2 Sheets-Sheet 1 I m /l2 2v" A w l//l/ /h. v V

Fig.1

INVENTOR SAMUEL M BAGNO A 6 EMT Dec, 15, 1964 s. M. BAGNO 3,161,742

' MAGNETIC INTRUDER AND FIRE DETECTOR Filed Aug. 24, 1961 2 Sheets-Sheet 2 lNVENTOR SAMUEL M BAGNO United States Patent 3,161,742 MAGNETKI ENTRUBER AND FIRE DETEQTQR Samuel M. Bagno, liellcville, N.J., assignor to Specialties Development Qorporation, lielleville, N..l., a corporm tion of New .l'erscy Filed Aug. 24, 19611, Ser. No. 133,714 1 Claim. (@l. Milk-87) The present invention relates to intruder detectors, and, more particularly, to such detectors which includes devices responsive to the opening of means of access to the protected area such as doors, windows and the like.

intruder detectors have been utilized in the past which include a magnetically operated switch mounted in the frame of each protected door and window, and a co operating magnet mounted in the moveable portion of each of the protected doors and windows to normally place the switches in the closed position, so that when a door or window is opened the magnet is moved away from the switch and the switch opens to actuate an alarm.

These previously known systems, however, may be defeated by moving a second magnet into the position occupied bythe magnet in the door, as the door is opened, to hold the magnetically operated switch in its closed po sition.

Accordingly, it is an object of the present invention to provide an improved intruder detector not subject to being defeated.

Another object is to provide such a detector capable of giving different indications in reponse to different conditions.

7 Another object is to provide such a detector which gives an indication in response to the presence of a fire in the protected area.

Another object is to provide such a detector which is capabie of giving plural indications over a two wire line.

A further object is to provide such a detector which is simple, reliable and easily adjusted.

Other and furtherobjects of the invention will be obvious upon an understanding of the illustrative embodiment about to be described, or will be indicated in the appended claim, and various advantages not referred to herein will occur to one skilled in the art upon employment of the invention in practice.

In accordance with the present invention, the foregoing objects are accomplished by providing a detector for giving an indication in response to the opening of a closure having adjacent moveable and stationary portions, comprising first and second magnetically actuated switch means adapted to be positioned in one of the closure portions, magnet means adapted to be positioned in one of the closure portions to act on only the second switch means, second magnet means adapted to be positioned in the other of the closure portions from the first switch operating means to be effective when the closure is closed to operate the first switch means and balance the action of the first switch operating means on the second switch means to prevent the operation thereof, and means for giving an indication when the condition of any of the switch means changes.

A preferred embodiment of the invention has been chosen for purposes of illustration and description, and is shown in the accompanying drawings, forming a part of the specification, wherein:

FIG. 1 is a vertical sectional view of a doorway and of a detector unit in accordance with the present invention mounted in the doorway for intruder detection.

FIG. 2 is a sectional view taken along line 2-2 on FIG. 1.-

FIG. 3 is a schematic wiring diagram illustrating the details for monitoring the condition of a number of the detector units such as shown in FIGS. 1 and 2.

Referring to the drawings in detail, and more particularly to FIGS. 1 and 2 thereof, there is shown a doorway including a door fill and a frame portion ill, in which a detector unit 12 is mounted.

The detector unit 12 includes a switch assembly 14 mounted in the frame member Ill and a magnet assembly 15 mounted at the upper edge of the door in for alignment with the switch assembly 14 when the door is closed.

The switch assembly 14 comprises two magnetically operated switches to and 17 and a permanent bar magnet 18 positioned within a body 19. The body 19 is in sorted in a recess 2d provided in the frame 11 and is held therein by a non-ferromagnetic metallic plate 21 secured to the frame member Till by counter-sunk screws or other suitable means (not shown). The

switches

16 and 17 inciude a cylindrical casing 22 of non-ferromagnetic material having end walls 2-4;, and a pair of contact arms 25 of ferromagnetic material. The contact arms 25 extend inwardly from opposite walls 24 along parallel spaced planes and have coextensive contact portions 2% adapted to be moved together to establish electrical contact between the arms. The

switches

16 and 17 are positioned adjacent the lower edge of the body 119 to be within the magnetic field of the magnet assembly 15 when the door is closed, and the permanent magnet 13 is positioned above the switch 17, whereby the switch 17 is also within the magnetic field of the magnet 28.

The magnet assembly 15 is mounted in a recess 27 in the top of the door iii and includes a cylindrical permanent magnet 29 and a non-ferromagnetic metal plate 30 positioned to enclose the recess 2];

The cylindrical magnet 29, as shown in FIG. 2, is positioned with its longitudinal axis vertically disposed, and is formed with diametrically opposite north and south poles disposed in a plane generally parallel with the switches 16 and E7. The poles of the magnet 29 are positioned opposite to those of the magnet 18 so that the fields of the magnets are in opposition.

When the door is clsoed, the flux path of the magnet 29 extends from the north pole thereof through the switch assembly 14 to the south pole of the magnet 29. This magnetic flux tends to create an induced magnetism in the contact arms 25 of the switches to and 17 such that the arms are attracted to each other. The switch 16 is effected only by the field of the magnet 29 which isof sufficient strength to cause the contact arms 25 therein to move together and establish electrical contact when the door is closed.

Theswitch 17, however, is under the influence of both the rnagnet 29 and the oppcsiteiy poled magnet 18. It will be seen, therefore, that by adjusting the field of the magnet 29, the effects of the magnets upon the switch It? may be made to balance each other so that the switch 17 will remain open when the door is closed.

With the field of the magnet 29 so adjusted, the switch 16 is closed and the switch 117 is open when the door is closed, and, when the door is opened, the switch 16 opens and the switch 17 is ciosed by the field of the magnet 18 which is no longer balanced by the magnet 29.

The effect of the magnet 29 upon the switch 17 is ad justed by altering the rotational position of the magnet with respect to the switches 16 and 1'7, thereby chang ing the angle at which the lines of force of the magnet intersect the switches. To decrease the effect of the magnet Zh upon the switch 17, the magnet is rotated away from the position in which the lines of force are parallel to the axis of the switches, and to increase the effect of the magnet it is rotated toward that position.

To facilitate this adjustment, a disc 31 having a slot 32 enemas therein is secured to the upper surface of the magnet 29, and a bore 34 is provided in the plate 30 to permit the insertion of a screwdriver or like tool in the slot, when the door is open, to effect rotation of the magnet.

To make the detector unit 12 responsive to the presence of a fire, the plate 21 is provided with a recess 35 in which is positioned a sheet 36 of ferromagnetic material of the type which loses its ferromagnetic properties at a relatively low temperature known as the Curie point temperature of the material.

An example of such a material is an alloy composed of about 31.35% nickel, about 11.80% chromium, and about 56.85 iron by weight which alloy is known as Midvale El. 562.

The magnet 29 is adjusted so that under normal temperature conditions, wherein the sheet 36 exhibits ferromagnetic properties, the magnetic fields are balanced to open the switch 17 as described above. Under these conditions the sheet 36 partially shields the switch assembly 14 from the field of the magnet 29. It will be seen, therefore, that a fire in the vicinity of the detector unit 12 will heat the sheet 36 above its Curie point and eliminates its shielding efiect. The field strength of the magnet 29 in the vicinity of the switch 17 is thereby increased, destroying the balance of the magnetic fields, and the switch 17 closes.

. While the detector unit 12 is described herein as being positioned within a doorway of the premises to be protected, units of this type can likewise be mounted within any Window or other closure having a stationary or frame member and a moveable member and which is capable of being utilized as an entrance to the premises.

As shown in FIG. 3, the switches 16 of all the detector units 12 within a protected premises 37 are connected in series with each other and with a current limiting resistor 39 between a pair of conductors & and ll leading from the premises 37 to a monitoring station 42. The switches 17 of the detector units 12 are each connected between ground and the side of the associated switch 16 which is connected most directly to the conductor 40, and a ground connection is supplied at the junction of the resistor 39 and the conductor 41.

Within the monitoring station 42, a battery 44 is connected in series with the winding 45 of an overload relay 46 and the winding 47 of an underload relay 49 between the

conductors

40 and 41. The overload relay 46 includes a pair of contacts 50 spring biased toward the open position and the underload relay 49 includes a pair of contacts 51 spring biased toward the closed position. Each of the contact pairs 50 and 51 are connected in series with an indicating lamp 52am] 54 respectively, and these series circuits are connected in parallel across the terminals of a battery 55'.

In operation, when the detector units 12 are adjusted as described hereinbefore and all of the protected closures (doors, windows, etc.) are closed, all of the switches 16 areclosed and all of the switches 17 are open, as shown in FIG. 3. A current then flows from the battery 44 through the switches 16, the resistor 39, and the relay windings 47 and 45. The circuit elements are chosen such that this current tlow is sufiicient to open the contacts 51 but is not suflicient to close the contacts th, therefore, neither of the lamps 52 nor 54 are lighted.

Should one of the protected closures be opened, the associated switch 16 opens and its companion switch 17 closes. Since the circuit from the monitoring station 42 through the closed switch 117 does not include the current 4:1. limiting resistor 39, the current flow is increased and the contacts close the light the lamp 52 giving an alarm.

It will be seen that the presence of the normally bal anced magnetic switch 17 makes it virtually impossible to defeat the present system by sliding a magnet into position as a protected door (or window) is opened. It the substituted magnet is stronger or weaker or oriented differently than the magnet assembly 15, the switch 17 will close in response to the resulting unbalanced magnetic field and the lamp 52 will light.

Should one of the conductors .9 or 41 be severed or broken the current tlow through the relay windings ceases and the contacts 51 close to light the lamp 54 giving a second alarm.

Also, should a fire occur in or adjacent to the protected premises the sheet 36 when heated above its Curie point temperature will lose its shielding effect upon the field of the magnet assembly 15 and the switch 17 will close in response to the resultant magnetic field thus lighting the lamp 52.

From the foregoing description, it will be seen that the present invention provides an intruder detector which is virtually impossible to defeat and is capable of giving plural indications over a two wire line in response to the opening of a closure, tampering, or the presence of a fire.

As various changes may be made in the form, con struction and arrangement of the parts herein, without departing from the spirit and scope of the invention and without sacrificing any of its advantages, it is to be under stood that all matter herein is to be interpreted as illustrative and not in any limiting sense.

1 claim: 7

In a detector for giving an indication in response to the opening of a closure having adjacent relatively movable first and second portions, the combination of a magnetically operated switch carried by said first closure portion, first magnet means carried by said first closure portion producing a magnetic field having sufficient strength to operate said switch, second magnet means carried by said second closure portion producing a magnetic field opposing that produced by said first magnet means, a metallic member carried by one of said closure portions and positioned between said second magnet means and said switch when said closure is closed to partially shield said switch from the field of said second magnet means at normal temperatures, said second magnet means producing a magnetic field of sufiicient strength at said switch to balance that produced by said first magnet means at said switch for preventing the operation of 'said switch at normal temperatures when said closure is closed, said metallic member being of a ferromagnetic material having a Curie point temperature such that said member loses its magnetic shielding properties when exposed to the heat of a tire so that the efiect of said second magnet upon said switch increases and said switch is operated.

References titted in the file of this patent UNITED STATES PATENTS 2,877,361 Chase Mar. 10, 1959 2,912,540 Sawicki Nov. 10, 1959 2,924,682 'Winterburn Feb. 9, 1960 3,008,019 Scheidig Nov. 7, 1961 3,009,047 Simmons Nov. 14, 1961 FOREIGN PATENTS 849,945] Great Britain Sept. 28, 1960