US 3184727 A
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Description (OCR text may contain errors)
y 1965 B. F. MIESSNER 7 ALARM SYSTEM Filed. Sept. 10, 1962 26 27 x52 10 I 53 69 45 as i Z INVENTOR.
6O BENJAMIN F. MIESSNER BY .II
ATTORNEY United States Patent 3,184,727 ALARM SYSTEM Benjamin F. Miessner, Miami Shores, Fla, assignor to Miessner Inventions, Inc, Miami Shores, Fla, a corporation of New Jersey Filed Sept. 10, 1962, Ser. No. 222,331 1t Claims. (Cl. Nth-227) This invention relates to an alarm system, and more particularly to a temperatureor tire-alarm system. In one aspect the invention is concerned with a particularly simple arrangement for and manner of triggering the alarm into operation. In another aspect it is particularly concerned with such a system which may be provided in simple and inexpensive form at each of as many sensing locations as may be desired but which, for great effectiveness of the alarm signal which it yields, is supplemented by or includes more expensive apparatus which for other purposes is almost always already present in the premises to be protected.
The invention uses as an underlying element an electrical buzzer, which may be basically or in general of the conventional form comprising an electromagnet, a vibratable armature system attractable by the electromagnet, and a pair of contacts in circuit with the electromagnet and repetitively closed and opened by the armature system when that system vibrates; such a buzzer of course itself provides an alarm if set into operation under the conditions of which alarm is to be given. According to the first aspect mentioned above, instead of placing the buzzer in oper- U ation by a separate thermostat or other sensor, the buzzers armature system itself is made deflectionally responsive to ambient temperature-the buzzers contacts being normally open but being brought into initial closure, thereby starting a sustained operation of the buzzer, by the thermally induced deflection of the armature system. Specifically, the armature system may for the purpose include a contact-operating arm and this arm may be a. thermally deflectible one, for example a bimetallic arm.
The second aspect mentioned above concerns the nature of the alarm signal which is given. An alarm will of course be given by the buzzers own acoustic output, augmented if desired by a bell rung by the vibrating armature system; it may further be given by an electric lamp operated whenever the buzzer operates, connected for example in series with the buzzer. Either or both of these signals may be of limited attention-arresting effectiveness, however-especially when the first aspect (briefly described above) is incorporated, for then the buzzer itself is inherently to be placed at the sensing location, at which those whose attention should be arrested by the alarm may not be present. According to the second aspect of the invention there is given another form of signal-i.e., a strong buzz from radio or television apparatus located at one or another place in the premises of interest, which either is being used for entertainment-program reception or is kept turned on in oil-tuned (i.e., tuned away from any program) condition. This is arranged for by connecting with the buzzer appropriate means for generating and propagating buzzer-modulated strongly damped and therefore highly interfering radio-frequency oscillations, which will influence the radio or television apparatus, to be thereby demodulated and the modulation thereof radiated as sound, however within its tuning range that apparatus be tuned.
In accordance with typical sub-aspects of the invention the generation of such oscillations is accomplished by providing at least one oscillatory electric circuit tuned to a radio freque cy and serially including the contacts of the buzzer. At each opening of those contacts such circuit or circuits will be excited into radio-frequency oscillation at Patented Max:718, 1955 its or their natural frequency; the excitation being impulsive in nature, the oscillations are inherently damped, beside which the inter-contact are which is normally characteristic of buzzer operation greatly increases the damping over what it otherwise would be. In turn the propagation of such oscillations may be accomplished by making the oscillatory electric circuit itself a radiating circuit, or by connecting thereto a short antenna, or by coupling that circuit to the electric wiring system to which the buzzer is connected and to which the radio or television apparatus is also connected; typical specific coupling arrangements for such purpose are described hereinafter.
Various objects of the invention have been made apparcut by the foregoing brief description. Allied and other objects will appear from the following detailed description and the appended claims.
In the description of the invention hereinafter set forth reference is had to the accompanying drawings, in which:
FEGURE l is a plan view of a buzzer such as mentioned above, together with a schematic showing of various associated components according to the invention as well as of nearby radio and television apparatus such as mentioned above;
FIGURE 2 is a fractional plan view of a modification of a portion of the buzzer of FIGURE 1; and
FIGURES 3 through 5 are simplified schematic views showing the electrical circuitry under respective conditions of component choice and arrangement.
Reference being had to FIGURE 1 there will be seen a metal plate 1 which may be mounted (as by the use of screw-holes Z) in any desired orientation but which for purposes of description may be assumed to be horizontal. Along opposite sides of the plate 1 it may be folded upwardly to form the vertical side flanges 5 and 6. To the left-shown flange 5, for example a little to the rear of its fore-and-aft center, there may be secured as by screw 8 one end of the iron core 9 of an electromagnet Iii, which extends from flange 5 toward flange 6 and which is provided with the coil 11 having terminal leads 12 and 13.
To the flange 6, for example close to the front, may be. assembled the forward portion of an armature system 29. This forward portion may for example be a generally J-shaped leaf spring 21, the shorter leg of the J being insulatedly secured to the flange; such securing may conveniently be achieved by a screw 17 and nut 18, the screw passing outwardly through the shorter leg of the spring 21 and through two shouldered insulating bushings 16 which are partially inset from opposite faces of the flange 6 within an aperture 7 in that flange. The main portion of the armature system 28, designated as 22 and itself hereinafter described, is an arm extending rearwardly from the longer leg of the spring 21. The arm 22 has a region in alignment with the core 9 of the electromagnet and in that region may carry an armature proper, designated as 25. To the arm 22 near its rearward extremity there may be secured a rearwardly extending light leaf sping 26 which curves first toward flange 6 and then into approximate parallelism with 22, and near its rearward extremity the spring 26 may carry a contact 27. A second contact 28, normally in spaced relationship to the contact 27, may be formed by the lefthand end of a screw 29; this screw may be threaded leftwardly through the flange 6 (thus making electrical contact with the plate 1) opposite the contact 27, and may be locked in any adjustment as by nut 3d.
The pair of contacts 27-28 is placed electrically in series with the electromagnet 16) by connection of the terminal lead 12 of the latter to the screw 17. The other terminal lead 13 of the electromagnet may be connected to a screw 33 passing through the flange 5, for example close to the front, but insulated therefrom as by bushings 32 (just as sleeve? screw 17 is insulated from flange 6 by bushings 16) and held in place as by nut 34.
The elements thus far described will be recognized as constituting a conventional buzzer one of whose electrical terminals is screw 33, the other such terminal being .any convenient point on the plate 1 such for example as a screw 35 threaded through flange near the rear and locked in place as by nut 36. Those buzzer terminals may be connected, as schematically indicated by plug 38, across a source of voltage, either AC. or D0, which may typically be an electric wiring system (i.e., line) or, when A.C. is employed, the secondary of a step-down transformer (not shown) whose primary is connected across such a system.
It will be understood that it prior to connection of the buzzer to the source that contacts 27-23 were to be just touching each other with very small pressure, then upon such connection the attraction of the armature and with it the arm 22 by the energized electromagnet would move the armature system to the left, or counterclockwise about the region of its securing to the screw 17, the spring 21 being thereby constrained. In the initial part of this leftward movement the contacts 2123 would open, deenergizing the electromagnet; throughout that movement the kinetic energy of the leftwarlly moving armature system would be progressively transferred into potential energy stored in that spring, and when it was fully transferred the leftward movement would stop and there would begin a rightward movement under the influence of the constrained spring Zll. These leftward and rightward movements would represent the initial leftward approximate half-cycle of a vibration of the armature system which would be a sustained vibration in view of the temporary re-energization, through contacts 27-28, of the electromagnet during each rightward approximate halfcycle. Such a sustained vibration constitutes the operation of the buzzer; acoustically it will be audible in its own right, and it moreover may be used to ring (i.e., repetitively to strike) a bell such as 49 (mounted on an extension 3 of the plate ll) through the well-known expedient of providing a clapper 41 carried at the end of a light arm 42 forming an extension of the arm 22.
The invention contemplates that the buzzer will be placed in operation in response to abnormal-typically, abnormally high-ambient temperature. While to accomplish this result various means may be employed, 1 have found especially simple and dependable a means comprised in the armature system Zli, and more specifcaliy a means comprised in the arm 22. For this purpose that arm may be and has been illustrated as a bimetallic element-i.e., an element consisting of two layers respectively of materials of different coeflicients of thermal expansion and held together in any suitable manner, a typical characteristic behaviour of the element being a bowing in one direction in response to increase, and a bowing in the opposite direction in response to decrease, of its temperature above and below a temperature at which it is essentially straight. In FEGURE 1, which is arranged for operation of the buzzer at abnormally high ambient ten peratures, the arm 22 will be arranged to how so as to defiect the rearward or free part of the armature system to the right, as indicated by the arrow traversing that arm.
With an arm, and thus an armature system, which is deflectible in response to ambient temperature, as is the bimetallic arm 22, I adjust the contacts 212?; (as by screw 29) so that they are open normally (i.e., at normal ambient temperature)-by a spacing such that they will be just closed when the arm has been heated to a preselected temperature, say 130 F, at which it is desired that the alarm operate. Since the contacts are normally open the continuous connection of the buzzer to the source of voltage, which of course is contemplated, does not result in any consumption whatever of powerunless and until the arm 22, in response to a rise of ambient temperature, deflects sufficiently to close the contacts 27-28. Forthwith upon such closure the buzzer will be placed in operation.
Once the buzzer has been placed in operation it will, by reason of the magnitude of swing of the vibrating armature system, continue to operate even though the ambient temperature and the arm temperature drops back substantially toward, or in typical cases even to, normal; this is a desirable feature, since usually even a temporary rise of ambient temperature of sufficient degree to invoke the buzzer operation merits investigation. For the same reason it will continue to operate even though the ambient temperature increases very substantially above that at which the operation was initiated. With some sets of parameters (spacings, magnitude of arm deflection per degree temperature rise, spring constants and adjustments etc.) of the buzzer, however, it is possible that a suflicient and sufliciently sustained further increase of ambient temerature might deflect the arm 22 so much that the contacts 27-28 would thereafter remain closed, thus stopping the further operation of the buzzer. This possibility may be foreclosed by a slight elaboration of the armature system, such as is illustrated in FlGUlZE 2.
Herein in the armature system the bimetallic arm 22 is replaced by a simple arm 123 to which the armature 25 is secured. At the region where this arm 123 is joined to the spring 21 there may be secured to those elements a light leaf spring 124 which may extend for a short distance rearwardly from that region. To the rear portion of this spring 124 there may be secured the forward portion of a bimetallic arm 122 which extends rearwardly, for example to just beyond the contact 28, generally parallel with the arm 123, and it is to this bimetallic arm 122 that the spring Zd-again carrying the contact 27, from which contact 28 will again be normally spacedwill be spaced. Until the bimetallic arm 122 reaches a relatively high temperature (at least equal to that at which the buzzer operation is to begin) its exact disposition relative to the arm 123 will be wholly dictated by its own configuration and the spring 1 .24; thus the rightward bowing of the arm 122 and the attendant rightward deflection of its rear portion with increasing temperature may be arranged (by appropriate adjustment of screw 23) to initiate operation of the buzzer at the same arm temperature as in the case of the FIGURE 1 structure. The arm 122 is arranged, however, so that when it reaches the relatively high temperature mentioned above its rear portion will be foreclose dtrom deflecting further rightwardly in response to further temperature rise.
Such foreclosure is readily provided for, for example, by a small screw 121i threaded lettwardly through the bimetallic arm 122, passing through a suitable oversize aperture in arm 123, and carrying a locked nut 12% at an appropriate distance to the left of the latter arm. The foreclosure takes effect when the thermally induced bowing of the arm 122 has brought the nut into abutment against the arm 123; thereafter further bowing of the arm 122, though still permitted, will result not in further rightward movement of its rear portion but instead in a flexing of the spring 124. The nut 12h thus forms a means limiting the degree of displacement (by the bimetallic arm 122) of the contact 27 relative to the arm 123 (and armature 25 etc.), while the spring 124 forms a means relieving strain on the bimetallic arm 122 during further ambient-temperature change after the nut 12h has become effective. In this or an equivalent manner all risk of cessation of buzzer operation as a result of very large increase of ambient temperature may be obviated.
For rapidity of response of the system either of FIG- URE 1 or of FIGURE 2 it is desirable to minimize the heat capacity and thermal inertia of the bimetallic arm (22 or 122), the thicknesses thereof shown in the drawings having been chosen simply for clear illustration of the bimetallic nature of the arm and not as indicative of a preferred thickness.
In addition to the acoustic signal provided by the buzzer (and augmented by the bell, if employed) there may be provided a visual signal. This may be arranged for by a serially including, in one of the conductors from the buzzer to the source of voltage, an electric lamp l5the electrical constants of the lamp and buzzer being suitably related to each other and to the voltage of the source for proper operation of each, as will be understood. In the case wherein the system is to be connected to a line supplying a voltage of the order of 115 volts, the use of the series electric lamp permits the coil 11 to be wound for a voltage much less than that voltage and yet to be used without external voltage-reducing means such as a transformerresulting in an economical system in any case, and in one equally usable in the particular case wherein the line is a DC. line.
With the system as thus far described the acoustic signal suffers from the limitation that it originates at the point where the abnormal temperature is sensed and will not be heard beyond a zone of acoustic influence centered at that point. In turn the visual signal, while with suitably extended wiring it may be caused to take place at any desired point, is inherently of limited attention-arresting effectiveness, especially when in its environs the ambient light is high. An important aspect of the invention copes with these limitations by reliance on the facts that in many environments, especially in the home, radio or television receiving apparatus is in actual operation during much, and that such apparatus may readily and at small expense be kept (in off-tuned or purely stand-by condition) in operation during the balance, of each twenty-four hours.
According to this aspect of the invention there is connected with the buzzer a means for propagating buzzermodulated damped oscillations of a radio frequency lying within the tuning or other response range of nearly receiving apparatus of either of the types described above, which broadly are radio-frequency receiving apparatus. With that apparatus in operation, wherever within its response range it may be tuned, the damped oscillations thus propagated will be received in some degree, and de modulated and the modulation thereof radiated as sound, by that apparatus. Such reception, when (as may usually be expected) the frequencies of the oscillations of the tuning of that apparatus differ from each other, will be the better the more highly damped be the oscillations; the intercontact arcing which normally characterizes the operation of a buzzer insures susbtantial damping.
By way of specific example, there is provided an oscillatory electric circuit, comprising an inductor and a capacitor, tuned to a radio frequency and serially including the contacts of the buzzer. This circuit in FIGURE 1 is designated as St and comprises an inductor 52 and a capacitor 53 connected in series with each other and across the contacts--i.e., from screw 17 to the plate l, for example at the screw 29. Damped radio-frequency oscillations are produced in such a circuit in the following manner:
When the contacts just open, thereby interrupting the flow of current through the iron-cored electromagnet, a large inductive transient or kick is produced across them. This transient (a) contributes strongly to an are which thereupon occurs between the contacts, and (b) triggers the circuit 50, which is completed by the resist ance of that are, into oscillation at the frequency to which it is tuned. This oscillation continues at least for so long as the arc persistsbut with rapidly decaying amplitude, as a result not only of the effective resistances (at radio frequency) of the inductor 52 and capacitor 53 but also of the progressively increasing resistance of the elongating arc. What has just been described constitutes a strongly damped train of oscillations of the radio frequency to which the circuit 50 is tuned; this train is repeated at each cycle of the buzzers vibration, whose frequency is therefore a modulating frequency.
While good amplitude and substantial damping of the radio-frequency oscillations may be achieved even with relatively low source voltage (e.g., of the very general order of 10 volts), both the amplitude and the damping as well as the fractional part of the buzzers cycle through which the oscillation persists are substantially increased at higher source voltages. For this reason I prefer the use of a source of the order of volts (the lamp 45, or an equivalent resistance, still enabling the coil 11 to be wound for a lower voltage as mentioned above).
Thus the operation of the buzzer invokes, in the circuit 5t, buzzer-modulated strongly damped oscillations of the radio frequency to which the circuit 50 is tuned. Such oscillations have a highly interfering effect on radiofrequency receiving aparatus within any area over which they may be propagated-or in other words they will be quite readily received, and demodulated and the modulation thereof radiated as a buzzing sound, by such apparatus even though the latter be tuned to a radio frequency substantially different from that of these oscillations. To take advantage of this fact I propagate the oscillations from the circuit 56.
Such propagation over a range sufficient to be received by radio-frequency receiving apparatus within a typical home in which the apparatus above described is also located may be readily achieved simply by making the inductor 52 of a reasonably substantial diameter and leaving it unshielded or, preferably, shielded only insofar as its electrostatic field is concerned so that it is unshielded electromagnetically. Such preferred shielding as to the electrostatic field only may be accomplished for example by providing about the winding of the inductor 52 a toroidal winding 51 of which one end only is connected to one terminal (preferably a terminal connected to the plate It) of the inductor. Alternatively or additionally such propagation may be achieved by connecting an antenna such as 1 5 to a suitable point in the circuit 59, for example the point thereof which is connected to screw 17; such an antenna should, however, be of length sufiiciently restricted so that there is avoided excessive propagation which might unduly interfere with radio-frequency reception in the premises of strangers having no interest in the alarm or the events which it signals.
For good response thereto by a radio receiver tunable over the range from 550 to 1500 kc. and located elsewhere in the same premises I have satisfactorily employed an inductor 52 in the form of a small loop of five turns of wire and of about 3" diameter, with which a capacitor of about .04 mfd. has proven appropriate to tune the circuit to a frequency within that range. Such a receiver, for example powered by self-contained means, is schematically shown as '7!) in FIGURE 1.
While there may be a several-times discrepancy be tween the frequency to which the radio-frequency receiving apparatus is tuned and the frequency of the circuit Sit, a discrepancy of too many times may militate too seriously against the effectiveness of the system. Thus if the radio-frequency receiving apparatus from which the alarm is to be heard be a television receiver (such as schematically shown in FIGURE 1 as 72), which is tunable only over a much-higher-frequency range, it is desirable to use an inductor and a capacitor appropriately smaller so that the circuit will be tuned to some frequency within that higher-frequency range. To provide for alternative adaptation to radioand television-receiver response there may be simultaneously used two respective circuits-an arrangement which is illustrated in FIGURE 1 by the additional incorporation of a circuit 55, comprising inductor 57 (with electrostatic shielding 56, if desired) and capacitor 58, tuned as last mentioned and also connected between the screw 17 and the plate 1 (as at screw 29).
Radio-frequency receiving apparatus of the type powered by connection to an electric wiring system or line is often inherently characterized, and by the use of means themselves known and not herein necessary to show may always be made to be characterized, by response to radiofrequency oscillations which may be present (superimposed on the normal power) in that line, just as it other- Wise responds to radio-frequency fields to which its normal antenna or other collector is exposed. Thus with a line-connected television receiver '72 so characterized, or with a line-connected radio receiver '71 so characterized, an additional or alternative method of propagation of the buzzer-modulated damped radio-frequency oscillations may be their impression on the same electric wiring system or linedesignated as dti-as that to which such receiver or receivers is or are connected. When (as illustrated) that same line is utilized to power the buzzer such impression may be achieved by suitably coupling the oscillatory circuit or circuits (50 or 55 or both) to that line. In the disclosure of various means by which such coupling to the line may be simply achieved reference is made to the schematic FIGURES 3 through 5; among these FIGURE 3 is a simplified circuit of the buzzer and, for example, the circuit (it being understood that the omission of the second circuit is only for simplicity of the showing).
From FIGURE 3 it will quickly be apparent that the intercontact path, during that most significant part of each cycle of the buzzer operation while an arc is persisting, could constitute such a coupling; in the system as thus far described, however, the effectiveness of that coupling is substantially destroyed by the effective impedance (at radio frequency) of this electromagnet and by the resistance of the lamp 45 (if employed). Such effectiveness can be readily established, however, by shunting the electromagnet by a capacitor 63, here acting as a by-pass, and the lamp (if employed) by a by-pass capacitor at as shown (for optional inclusion) in FIG- URE 1, to result in the schematic circuit shown in FIG- URE 4. Then the inter-contact arc beomes an effective coupling of the circuit 5% to the line 8% and, if the receiving aparatus '71 or '72 is characterized in the manner above stated, the line may be relied on as the sole or a supplementary means of propagating the buzzer-modulated damped high-frequency oscillation.
The coupling of circuit to line need not be limited to the inter-contact arc. Thus, in FIGURE 1 I show the connection of the lower extremities of circuits Sit and to the screw 17 as made through a single-pole doublethrow switch 65, by throw of which the connection of those circuit extremities may alternatively be made to the line-ward terminal (screw 33) of the buzzer (it being understood that this switch is shown to illustrate alternative circuitry and not to imply that it need be physically present). Assuming the switch so thrown and the capacitor 63 (and capacitor 6t) around the lamp if the lamp be present) still to be employed, the circuitry becomes that shown in FIGURE 5. Now the oscillatory circuit comprises the inductor S2 and the capacitors 53 and 63 (the latter shunted by the electromagnet) as well as the contacts all in series with each other, and not only the inter-contact are but also the capacitor 63 form means coupling the circuit to the line.
For the circuit 50 in the case of the circuitry of FIG- URE 5 I have found satisfactory the use of capacitors 53 and 63 of a joint series value such as would be used for 53 alone in the FIGURE 3 case and with 63 of a few times the capacitance of 53. It is, however, possible to make 53 the larger and 63 the smaller, thereby further increasing the coupling.
In the circuitry of FIGURE 4 the predominately capacitive impedance presented by the line and by-pass capacitors 6t) and 63 in series with each other is shunted across the contacts, so that even when the contacts are wholly (i.e., non-arcingly) open there still exists an oscillatory circuit, thereby prolonging the duration of each train of damped oscillations; the tuning will of course then be shifted to a somewhat higher frequency but, since response by randomly tuned apparatus is desired, this tends to be advantageous rather than detrimental. In the circuitry of FIGURE 5 the predominately capacitive impedance presented by the line and by-pass capacitor 60 in series with each other is etiectively added to the capacitance of 63 while the contacts are closed and substituted for the latter when the contacts are wholly open, with eitects which in a general sense are qualitatively similar to those just discussed for FIGURE 4.
In a practical application of the invention to the protection of premises, for example a home, a number of units each consisting simply of a buzzer with the circuit Stl or circuits 5i and 55, with the lamp 45 if desired (and if not desired then preferably with an equivalent series resistor) and with any additional capacitor for capacitors which are to be employed in accordance with the foregoing, may be fastened or hung in respective areas where sensing is desired and each simply plugged into the nearest available electric-wiring-system outletthe extreme simplicity and low cost of each unit, and the total absence of power drain by each excepting when an alarm is to be given, permitting a generous distribution throughout the premises. it is then only necessary that, in the area where there are present those who should be apprised of the alarm, there be kept turned on (with a finite volume-control setting) some one radio-frequency receiving apparatus, either actually receiving some entertainment program or detuned when no such reception is desired.
While I have disclosed my invention in terms of particular embodiments thereof it will be understood that I intend thereby no unnecessary limitations. Modifications in many respects will be suggested by my disclosure to those skilled in the art, and such modifications will not necessarily constitute departures from the spirit of the invention or from its scope, which I undertake to define in the following claims.
1. In a temperature-or fire-alarm system, a buzzer connectible across a source of voltage and comprising an electromagnet, a vibratable armature system attractable by the electromagnet, a pair of contacts, said vibrata'ole armature system including a thermally deflectible element thermally coupled to ambient temperature, one of said contacts being mechanically coupled to said thermally deflectible element whereby to be subjected to displacement thereby, said contacts being open at normal ambient temperatures but being initially closed by said thermally defiectible element upon ambient-temperature change to a perdetermined ambient temperature, and circuit means interconnecting said contacts and said electromagnet whereby said vibratable armature system repetitively opens and closes said contacts after the initial closing of said contacts at the predetermined ambient temperature.
2. The subject matter claimed in claim 1 further including means limiting the degree of said displacement of said one contact by said thermally deflectible element, whereby to obviate thermally induced continuous closure of the contacts.
3. The subject matter claimed in claim 1 wherein said thermally deiiectible element is a bimetallic arm carrying said one contact near one of its extremities and resiliently mounted at its other extremity to other parts of the armature system.
4. In a temperatureor fire-alarm system, a buzzer connectible across a source of voltage and comprising an electromagnet, a vibratable armature system attractable by the electromagnet, a pair of contacts, the armature system constituting a means supporting one of said contacts, means external to the armature system supporting the other of said contacts, a thermally deflectible element comprised in one of said supporting means whereby the contact supported by that one supporting means is subject to displacement by said thermally deflectible element, said element being thermally coupled substantially only to ambient temperature, said contacts being open at normal ambient temperatures but being initially closed by said thermally deflectible element upon ambient-temperature change to a predetermined ambient temperature, and circuit means interconnecting said contacts and said electromagnet whereby said vibratable armature system repetitively opens and closes said contacts after the initial closing of said contacts at the predetermined ambient temperature.
5. The subject matter claimed in claim 4 wherein said thermally deflectible element is a bimetallic element.
6. The subject matter claimed in claim 4 in combination with an oscillatory electric circuit tuned to a radio frequency and electrically coupled to said contacts Whereby to be excited into damped radio-frequency oscillations modulated by the buzzer at the frequency of vibration of the armature system.
7. The subject matter claimed in claim 6 further includ ing means propagating said oscillations from said oscillatory circuit.
8. The subject matter of claim 7 in combination with radio-frequency receiving apparatus tunable over a given range, situated within the field of influence of the propare gated oscillations and, however tuned Within that range, responsive to those propagated oscillations.
9. The subject matter claimed in claim 4 further including means limiting said displacement of the contact supported by said one supporting means, whereby to obviate thermally induced continuous closure of the contacts.
10. The subject matter claimed in claim 9 further including means relieving strain on said thermally defiectible element during further ambient-temperature change after said limiting means has become effective.
References Cited by the Examiner UNITED STATES PATENTS 358,910 3/87 Wildt 340-402 1,106,432 8/14 Wilcox 340-403 1,497,194 6/24 Norden et al 340-224 2,141,775 12/38 Varley.
3,001,066 9/61 Naber et a1.
NEIL C. READ, Primary Examiner.