US3686605A

US3686605A - Thermostatic for fire alarm system

Info

Publication number: US3686605A
Application number: US200712A
Authority: US
Inventors: Charles John Hire
Original assignee: Fasco Industries Inc
Current assignee: Fasco Controls Corp
Priority date: 1971-11-22
Filing date: 1971-11-22
Publication date: 1972-08-22
Anticipated expiration: 1989-08-22

Abstract

A bimetallic, temperature-responsive disc is mounted for limited axial reciprocation in a generally cup-shaped metal housing between an internal, circumferential shoulder, which is formed in the housing adjacent its closed end, and a normally open, flexible switch arm, which is mounted in its open end. The closed end of the housing may be flexible, or it may house a reciprocable test button. Normally the disc is bowed toward the closed end of the housing; but when its ambient temperature exceeds a predetermined value, it flexes so that its edge engages the circumferential shoulder, and its center snaps in the direction of the switch arm far enough to close the latter. When the disc is in its normal state, the test button or flexible closed end of the housing may be pushed to shift the disc axially in the housing far enough to close the switch without flexing the center of the disc.

Description

[22] Filed:

United States Patent Hire 541 THERMOSTATIC FORFIRE ALARM SYSTEM [72] Inventor: Charles John Hire, Pittsford, N.Y.

[73] Assignee: Faseo Industries, Inc., Rochester,

Nov. 22, 1971 21 1 Appl. No.2 200,712

[52] US. Cl. ..337/334, 337/343, 337/380 [5 1] Int. Cl. ...H01h 13/52, HOih 37/04, HOlh 37/54 [58] Field of Search ....337/89, 91 334,343, 348,

1151 3,686,605 [451 Aug. 22 1972 Primary Examiner-lkmard A. Gilheany Attorney-B. Edward Schlesinger et al.

57 ABSTRACT A bimetallic, temperature-responsive disc is mounted for limited axial reciprocation in a generally cupshaped metal housing between an internal, circumferential shoulder, which is formed in'the housing adjacent its closed end, and a normally open, flexible switch arm, which is mounted in its open end. The closed end of the housing may be flexible, or it may house a reciprocable test button. Normally the disc is bowed toward the closed end of the housing; but when its ambient temperature exceeds a predetermined value, it flexes so that itsedge engages the circumferentialshoulder, and its center snaps in the direction of the switch arm far enough to close the latter. When the disc is in its normalstate, the test button or flexible closed end of the housing may be pushed to shift the disc axially in the housing far enough to close the switch without flexing thev center of the disc.

7 Claims, 5 Drawing Figures Patented Aug. 22, 1972 2 Sheets-Sheet 1 0 m a, m

all

FIG. 2

x f m m m N m E H s O N m J 2 m S w E A L R r A H C Md Y 1 B f s f 3 w M 7 3 K F 3 Q B S a W n F T x C Patented Au 22,1972 3,686,605

2 Sheets-Sheet z FIG. 5

INVENTOR CHARLES JOHN HIRE M ww ATTORNEYS the circuit.

THERMOSTATIC FOR FIRE ALARM SYSTEM This invention relates to thermostatic switches, and more particularly to a temperature-responsive switch particularly adapted for use in operating and testing an electrical fire alarm circuit.

Heretofore it has been conventional to employ temperature-responsive switches or thermostats for controlling electrically operated fire alarm devices. Typically, a normally open thermostatic switch is connected in series with an electrically operable alarm of the visual or audible variety. When the ambient temperatureof the switch exceeds a predetermined value, as for example when the switch is exposed, to excessive heat caused by a nearby fire, a temperature-responsive element in the switch causes the switch to be forced from its open to its closed position, thereby energizing the alarm.

Since under normal circumstances fire alarms of the type described are seldom triggered by an actual fire, it is essential that the alarm circuit be tested periodically to make sure that it is in proper operating conditions.

Usually this test is made possible by a second, normally open, manually operable switch, which is connected in parallel with the temperature-responsive or thermostatic switch, and which can'be closed momentarily to supply power to the alarm without actuating the thermostatic switch. 1

A major disadvantage of this conventional fire alarm is that the thermostatic switch is bypassed, or shunted out of the circuit, whenever the above-noted manually operable switch is closed to test the alarm. Since the thermostatic switch often remains in its normally open position for years, its contacts may become so corroded that, when the switch is finally closed as the result of a nearby fire, the corroded contacts will prevent power from being applied to the associated alarm. Since usual testing procedures cause power to bypass the thermostatic switch, there heretofore has been no satisfactory way to detect any such fault that may have developed in the thermostat subsequent to its initial installation in The primary object of this invention is to provide a temperature-responsive thermostatic switch that avoids the disadvantages of prior such switches. To this end it is a further object of this invention to provide a thermostatic switch which is calibrated to operate automatically in response to a predetermined increase in its temperature ambient, and which can be readily operated manually without altering its calibration.

A further object of this invention is to provide an improved fire alarm circuit which is more reliable, and requires the use of fewer switches than prior such circuits. Another object of this invention is to provide an improved thermostatic switch containing a flexible temperature-responsive element that flexes automatically to close an adjacent switch upon predetermined changes in ambient temperature, and which is movable manually and without flexing, to effect closure of said switch for test purposes.

Other objects of the invention will be apparent I hereinafter from the specifications and from the recital of the appended claims, particularly when read in conjunction with the accompanying drawings.

In the drawings:

FIG. 1 is a plan view of a thermostatic switch made in accordance with one embodiment of this invention;

FIG. 2 is a sectional view of this switch taken along the line 2-2 in FIG. 1 looking in the direction of the arrows;

FIG. 3 is a wiring diagram illustrating one manner in which this switch may be wired for operation in a fire alarm circuit;

FIG. 4 is a plan view of a modified switch made in accordance with a secondembodiment of this invention; and

FIG. 5 is a sectional view of this modified switch taken along

line

5,5 in FIG. 4 looking in the direction of the arrows.

'Referring now to the drawings by numerals of reference, and first to the embodiment shown in FIGS. 1' and 2, l0 denotes generally a thermostat or a temperature-responsive switch comprising an inverted, can

or cup-shaped metal housing 12 having a downwardly wall 13 with the closed end of the housing. Press-fit in the lower open end of wall 13 is-a circular disc or base 15, which is made of dielectric material. On its upper or inner face the base 15 has an integral, dome-shaped projection 16 that faces the closed end of the housing.

Two right-

angular terminals

18 and 19 are secured each at one end to the underside of the base 15 by

rivets

20 and 21, respectively, so that opposite ends of the terminals project downwardly out of the housing in spaced, parallel relation. Secured at one end to base 15 beneath the inner end of rivet 21, and extending over projection 16 and transversely across the center of housing 12, is a flexible, electrically conductive switch arm 22. On its opposite, free end, arm 22 has a metal contact 23, which normally is held resiliently by arm 22 in spaced, confronting relation to the inner end of rivet 20. As shown more clearly in FIG. 2, arm 22 is bent intermediate its ends so that its central portion 24 curves over the top of the base projection 16 normally to be disposed in spaced relation thereto.

Mounted to reciprocate in a central opening 26 in the upper, closed end of housing 12 is a cylindrical test button or pin 28. On its inner end pin 28 has a discshaped head 29, the diameter of which is larger than that of the opening 26.

Mounted in housing 12 between pin 28 and the switch arm 22 is a temperature-responsive, bimetallic disc 30, which is calibrated so that at room temperature it will be bowed upwardly, or toward the closed end of housing 12 as shown in FIG. 2. Also, the diameter of disc 30 is slightly less than the inside diameter of the annular wall 13 of the housing 12; and a marginal portion of the disc adjacent its periphery registers with the internal shoulder 14 on the housing. Consequently the disc 30 is free to move axially within the annular wall 13 between switch arm 22 and the housing shoulder 14.

Interposed between the disc 30 and the switch arm 22 is a thin, disc-shaped layer 32 of flexible, dielectric insulating material, which may have approximately the same diameter as the disc 30. Layer 32 insulates disc 30 electrically from switch arm 22.

When the switch 10 is assembled, its base 15 is inserted partway into the lower end of wall 13; andthespace in the housing beneath base 15 is then filled or potted with a layer 35 of epoxy resin, or the like, which operates to secure the base 15 in a stationary position in the housing. At this time, assuming that switch is at room ambient, the switch 22 will be open, and the disc 30 will be bowed upwardly at its center (FIG. 2) toward the inner end 29 of test button 28. Moreover, the central portion 24 of the now-open switch are 22 maintains the marginal edge of disc 30 in close proximity to the shoulder 14.

In FIG. 2 the slight space illustrated between the marginal edge of thedisc 30 and the shoulder 14 is exaggerated merely for purposes of illustration.

In use, the thermostat 10 is connected in circuit with a conventional, electrically operable fire alarm 34 (FIG. 3), and with an electrical power supply, such as for example a battery 35, or with an alternating current power source (not illustrated). In the illustrated circuit the alarm 34 is connected at one side-by a wire or line 36 with the terminal 18, and at its opposite side by line 37 to one terminal of the battery 35. The opposite terminal of battery 35 is connected by a line 38 with the thermostat terminal 19, so that thermostat 10 is operatively connected in series with the alarm 34.

When a nearby fire, for example, causes the ambient temperature of the thermostat 10 to rise and exceed the critical value for which the disc is calibrated, the marginal edge of the disc will snap upwardly (FIG. 2)

into engagement with the shoulder 14, and its center will snap or bow downwardly to drive the switch arm 22 to closed position in which its contact 23 engages the inner end of the rivet 20, thereby electrically connecting

terminals

18 and 19 and energizing alarm 34.

When the ambient temperature thereafter drops or falls below the above-noted critical value, the center of disc 30 will automatically snap back (upwardly in FIG. 2) to its original position or state, thereby allowing resilient arm 22 to disengage its contact 23 from rivet 20, and thereby to deenergize alarm 34.

For test purposes, and assuming disc 30 is in it's normal state, an operator need only to push the test button 28 (FIG. 3) into housing 12, and against the upwardly bowed (FIG. 2) center of disc 30, to shift the disc axially in the annular housing 13 away fromshoulder 14 far enough to urge the switch arm 22 momentarily to closed position. If the confronting surfaces of the switch contact 23 and the inner end of the rivet 20 are in operating conditioni.e., they are free of any excessive corrosion that might block current flow through the switchthe circuit from the battery to the alarm 34 will be completed, and the alarm will be energized. This testing operation thus tests the operating condition of the entire alarm circuit, including the thermostat 10. As soon as the operator releases the test pin 28, the resilient switch arm 22 will urge the disc 30 and pin 28 back to the normal rest position (FIG. 2), thereby once again opening the circuit to the alarm 34.

In FIGS. 4 and 5, wherein like numerals are employed to denote elements similar to those employed in the embodiment of FIGS; 1 and 2, 40 denotes a modified thermostat in which the switch arm 22 and disc 30 are completely enclosed in an inverted, can or cup-shaped metal housing 42, which is slightly different in configuration from the housing 12 employed in the first embodiment. As in the case of thermostat l0, disc 30 is mounted for limited axial reciprocation in an annular wall portion 43 of housing 42 between switch arm 22 and an internal, circumferential shoulder 44, which is formed in housing 42 adjacent its closed end. Disc 30 also is normally bowed toward the closed end of housing 42. Thus when its ambient temperature exceeds a predetermined value, the edge of disc 30 will snap suddenly against shoulder 44, and its center will bow downwardly to close switch arm 22 in the same manner as described above in connection with switch 10.

Thermostat 40, however, does not have a test button 28 for manually closing arm 22. Instead, the closed end of housing 42 is provided with a plurality of concentric,

circular corrugations 46 disposed coaxially on wall 43 and disc 30. These corrugations enable the closed end of housing 42 to be forced or pushed manually inwardly far enough to shift disc 32 axially in wall 43 a sufficient distance to effect momentary closing'of switch arm 22, thereby to test an alarm circuit of the type shown in FIG. 3, when thermostat 40 is employed in such circuit in place of thermostat 10. When pressure is removed from the closed end of housing 42,. its closed end'will return to its normal position (FIG. 5) to allow arm 22 to reopen. As in the case of thermostat 10, this axial movement of disc 30 will not cause the disc to be flexed, nor will it alter the calibration of the thermostat.

From the foregoing it willbe apparent that the instant invention provides comparatively simple and reliable means for enabling both automatic and manual operation of a fire alarm system of the type described. By operating the pin 28 in housing 12, or the corrugated end of housing 42, manually to close the circuit to the alarm 34, both the alarm itself and the associated

thermostat

10 or 40 are testedsimultaneously for any faults that might have resulted in the circuit through prolonged disuse. In particular, any malfunction of the

thermostat

10 or 40 that might otherwise result through excessive corrosion or oxidation of its switch contacts is readily detected. This contrasts with the conventional method of testing a fire alarm circuit by use of a normally open, manually operable switch which is connected in parallel with the alarm controlling thermostat, as illustrated for example by the switch S shown by broken lines in FIG. 3. The invention therefore also reduces the number of switches heretofore required in an alann circuit of the type described, thus reducing the complexity and cost of the circuit.

Furthermore, when testing an alarm circuit incorporating a thermostat of the type described herein, the entire bimetallic disc 30 is shifted axially within the

annular wall

13 or 43 so that it is not necessary, in executing such tests, to flex the center of the disc 30 from one to the other of its two positions of bow. Consequently the test will not alter the calibration of the thermostat, which might be the case if the test were to be conducted by forcing the center of disc 30 from one to the other of its two positions of how while at room temperature. Since the disc 30 is bounded only at its upper side by the

shoulder

14 or 44, and is free at its underside to shift axially downwardly in

wall

13 or 43, a distance at least equal to the space normally separating the contact 23 from rivet 20, the edge of the disc 30 is not subjected to any external stress during the testing operation and the disc therefore will remain properly calibrated. Moreover, the thermostat 40 has the particular advantagethat'its switch contacts and disc 30 are completely sealed within housing 42 above base 15,

so that dust or other foreign matter cannot enter the housing to interfere with proper operation of the switch.

Having thus described my invention, what I claim is:

l. A thermostat, comprising ahousing,

a pair of electrical terminals projecting from said housing,

a normally open switch in said housing operatively connected between said terminals electrically to connect said terminals to each other, when closed,

bimetallic, temperature-responsive element mounted in said housing for limited reciprocable movement in its entirety toward and away from said switch selectively to close and open the latter, and operative when the ambient temperature of the element exceeds a predetermined value, to have a portion only thereof flex toward said switch to close the latter, and means on said housing operable from the exterior thereof to force said element toward said switch far enough to close said switch without causing said portion of the element to flex. 2. A thermostat as defined in claim 1, wherein said switch comprises a stationary contact and a movable contact normally urged resiliently into spaced confronting relation to said stationary contact,

said element is a movable disc interposed between said movable contact and said means and having a flexible center portion normally bowed in the direction of said means for engagement thereby when said means is operated to close said switch, said portion being operative automatically to flex and bow in the direction of said movable contact when said ambient temperature exceeds said predetermined value, and

a shoulder is formed on the inside of said housing to engage the marginal edge of said disc on the side thereof remote from said movable contact to limit the movement of said disc toward said means, and to act as a fulcrum and cause said center portion of said disc to force said movable contact against said stationary contact, when said center portion flexes toward said movable contact.

3. A thermostat as defined in claim 1, wherein said means comprises a pin reciprocably mounted intermediate its ends in the wall of said housing normally to project exteriorly thereof, and engageable at its inner end with said element to force the latter to its switch closing position when pressure is applied to the outer end of said pin.

4. A thermostat as defined in claim 1, wherein said means comprises a plurality of corrugations formed in the wall of said housing in confronting relation to said element and operative, when pressure is applied thereto from the exterior of said housing, to flex resiliently inwardly against said element to shift the latter to its switch closing position.

5. A thermostat, comprising a hollow housing'having an open end and a closed end,

a rigid base secured in the open end of said housing and spaced from said closed end, a'pair of spaced, electrical terminals secured to said base and projecting exteriorly of said housing an electrical contac connected to one of said terminals and projecting into the space between said base and said closed end of the housing,

a flexible switch arm having a fixed end secured in said housing to the other of said terminals, andhaving a free end extending transversely across said space normally to be disposed in spaced, confronting relation to said contact,

a disc-shaped, bimetallic temperature-responsive element mounted to reciprocate in said. housing between said switch: arm and an internal, circumferential shoulder formed in said housing adjacent said closed end thereof,

said element having a flexible central portion normally disposed in a first position in which it is bowed in the direction of said closed end, and

being operative, when its ambient temperature exceeds a predetermined value, to flex into a second position in which its marginal edge engages said shoulder, and its central portion is bowed in the direction of said switch arm far enough to force said free end of the arm into engagement withsaid contact, and

means on the closed end of said housing operable means comprises a reciprocable test button mounted intermediate its ends in an opening in said closed end of said housing in confronting, coaxial relation with said element.

7. A thermostat as defined in claim 5, wherein said means comprises a plurality of flexible, concentric corrug ations formed in said closed end of said housing in confronting, coaxial relation with said element.

Claims

1. A thermostat, comprising a housing, a pair of electrical terminals projecting from said housing, a normally open switch in said housing operatively connected between said terminals electrically to connect said terminals to each other, when closed, a bimetallic, temperature-responsive element mounted in said housing for limited reciprocable movement in its entirety toward and away from said switch selectively to close and open the latter, and operative when the ambient temperature of the element exceeds a predetermined value, to have a portion only thereof flex toward said switch to close the latter, and means on said housing operable from the exterior thereof to force said element toWard said switch far enough to close said switch without causing said portion of the element to flex.

2. A thermostat as defined in claim 1, wherein said switch comprises a stationary contact and a movable contact normally urged resiliently into spaced confronting relation to said stationary contact, said element is a movable disc interposed between said movable contact and said means and having a flexible center portion normally bowed in the direction of said means for engagement thereby when said means is operated to close said switch, said portion being operative automatically to flex and bow in the direction of said movable contact when said ambient temperature exceeds said predetermined value, and a shoulder is formed on the inside of said housing to engage the marginal edge of said disc on the side thereof remote from said movable contact to limit the movement of said disc toward said means, and to act as a fulcrum and cause said center portion of said disc to force said movable contact against said stationary contact, when said center portion flexes toward said movable contact.

5. A thermostat, comprising a hollow housing having an open end and a closed end, a rigid base secured in the open end of said housing and spaced from said closed end, a pair of spaced, electrical terminals secured to said base and projecting exteriorly of said housing, an electrical contact connected to one of said terminals and projecting into the space between said base and said closed end of the housing, a flexible switch arm having a fixed end secured in said housing to the other of said terminals, and having a free end extending transversely across said space normally to be disposed in spaced, confronting relation to said contact, a disc-shaped, bimetallic temperature-responsive element mounted to reciprocate in said housing between said switch arm and an internal, circumferential shoulder formed in said housing adjacent said closed end thereof, said element having a flexible central portion normally disposed in a first position in which it is bowed in the direction of said closed end, and being operative, when its ambient temperature exceeds a predetermined value, to flex into a second position in which its marginal edge engages said shoulder, and its central portion is bowed in the direction of said switch arm far enough to force said free end of the arm into engagement with said contact, and means on the closed end of said housing operable manually, when said temperature is below said predetermined value, to engage said central portion of said element, and to urge said element axially in said bore toward said switch arm a sufficient distance to cause said free end of the arm to engage said contact without flexing said central portion from its first to its second position.

6. A thermostat as defined in claim 5, wherein said means comprises a reciprocable test button mounted intermediate its ends in an opening in said closed end of said housing in confronting, coaxial relation with said element.

7. A thermostat as defined in claim 5, wherein said means comprises a plurality of flexible, concentric corrugations formed in said closed end of said housing in confronting, coaxial relation with said element.