US1982548A - Thermal switch - Google Patents

Description

Nov. 27, 1934. H STAVE 1,982,548

THERMAL SW1 TCH Filed March 50, 1935 17.? @m j y @E /I f7 Patented Nov. 27, 1934 UNITED `STATES PATENT OFFICE THERMAL SWITCH England Application March 30, 1933, Serial No. 663,579 In Great Britain March 30, 1932 12 Claims.

This invention relates to thermal switches, more especially .adapted for application as automatic fire detectors. The invention has for its objects to provide an improved device that is as before mentioned effectively responsive both to sudden rises of temperature and to slow longcontinued rises of temperature which exceed a definite and predetermined limit which will be reliable in its action and will not be materially affected by seasonal changes of temperature, so that in the case of a fire detector, for example, the device is substantially equally sensitive in summer and winter.

The invention consists of an improved coni struction and is characterized in that two thermal elements are arranged one above or to thel side ol' the other bridging an insulating base and are so constructed and yarranged that upon a rapid temperature change a differential distortion of the two elements operates to establish an alarm circuit through one pair of contacts and upon a slow temperature change a. substantially uniform distortion of both elements operates to establish an alarm circuit through a second pair of contacts. It will be apparent that on the same principles Aa switch according to the invention may be utiiized to open a closed circuit instead of closing 'an open one by suitably arranging the thermal or heat sensitive element.

According to the invention, moreover, the lheatsensitive elements are preferably of identical construction, but one may be covered or screened under such conditions that while it is not quickly responsive to rapid changes of temperature, its

' capacity to vary under slow changes of temperature does not differ sensibly from the capacity of the element that is not so covered or screened.

The form of the heat-sensitive elements and the manner in which they are mounted may be varied, however, without departing from the invention.

The invention further comprises the features hereinafter described and claimed.

The invention is illustrated, by way of example, in the accompanying drawing representing an automatic fire detector provided according to the invention, and an ,installation in which such detector may be used.

Figure 1 is a sectional elevation of the yfire detector.

Figure 2 is a plan view of the fire detector.

Figure 3 is an underside plan view of the fire detector.

Figure 4 is a cross-sectional elevation on the line 4 4 of Figure l.

Figure 5 is a. moss-sectional elevation on the line 5 5 of Figure l.

Figure 6 is a diagram of one system of connections for an installation in which four of the fire detectors are provided.

In carrying the invention into effect according to one arrangement the construction of an automatic fire detector as illustrated in Figures 1 to 5 of the accompanying drawing, there is provided a base a of porcelain or other non-conducting material having a low co-efiicient of expansion and whose length and width substantially correspond with those of lthe thermal or heat-sensitive elements b, c. At the ends, which are advantageously rounded, the base is provided with raised projections or bosses a1 to form seatings for the ends of the element c, the surfaces of the bosses being inclined downwardly towards the Imiddle ofthe base in order that the element c may set in position with a downward inclination. The lower ,face of the base at the ends is formed parallel with the inclined surfaces of the projections a1 and through the base there are formed bores or holes Aa2 disposed in directions which are normal to the main lower surface of the base and which in this construction are of elongated cross-section in the direction of the longitudinal axis of the base.

The elements b and c are provided as exible strips of a metal or alloy having a high co-eicient of expansion, such as phosphor-bronze, the strips being in this case identical in form and mass and being mounted upon the base a by means of fixing screws or bolts a3 which pass through the hotes a2 in the base and engage holes in the ends of the elements b, c. Distance members d in the form of ycollars of brass or other suitable material are mounted upon the screws or bolts a3 between the eiements b, c for the purpose of determining the .separation of the elements. It will be observed that '.by reason of the inclination of the surfaces of the projections a1 and the correspending p'mms of the lower surface of the base a, the bolts or screws a3 set at an inclination to the planes of the elements b, c when the latter are firmly secured in position.

In order that the screws or bolts a3 may form part of the circuits through the respective elements b, c each element is at one end formed with a hole for the screw or bolt of a diameter sufficient to admit an insulating washer e of mica or other suitable material. These enlarged holes are provided at opposite ends of the elements b, c that is to say, for the element c the enlarged hole for the reception ot the washer is disposed lto the left, while in the case of the element b it is disposed to the right. In the latter instance the element is further insulated from the bolt or screw a3 and its nut by mica or like washers f disposed above and below the element, while in the case of the element c a similar insulating washer is disposed below the collar d. The element b is provided at the middle of its length with a screwed socket g1 in which is received the contact screw g, the extremity of which extends midway between the two elements b and c and is shrouded by a sleeve of material such as steatite g2. A spring washer g3 is advantageously disposed between the head of the screw g and the socket gl. The element c is similarly provided with a screwthreaded socket h1 in which is received a contact screw h, the upper extremity of 'which extends into the steatite bush g2 so that it is normally positioned from the extremity of the contact screw g a distance of, for example, .00()5 of an inch. The air gap may -readily be adjusted by rotation of the screw g. The screw h also extends downwardly with clearance in a steatite or other insulating bush i kmounted within a screw-threaded metal bush il which is seated in a recess or boring a4 in the base a and is maintained in position by a nut i2.. The bush il is screw-threaded internally for the lower part of its bore to receive the contact screw j which may be adjusted in position by rotation. The insulating bush i may be made of some flexible insulating material, such, for example, asoiled silk.

VThe screws'or bolts a3 serve also to maintain on the lower face of the base a conducting strips lc, k1, the strip lc being extendedr and formed with a hole to receive the bush il so that it may be engaged by a nut i2.

The elements b, c are identical in form and material, 'and have therefore precisely the same capacity for expansion, but in order that the device may be responsiveto rapid rises of temperature, the element c is lagged or jacketed by coverings c1 of asbestos or similar heat-insulating material. Thus the element c is protected against rapid rises of temperature and does not materially change its disposition, but the element b, being without such protection, is caused to expand rapidly so that by its distortion or flexure the extremity 'of the contact screw g is brought into engagement with theextremity of the contact screw h tofclose a circuit including the screws or bolts a3 and the strips 1c, k1. In the case of a slow rise in temperature the lagging of the ele-.- ment c is ineffective to protect the element and thus the elements b, c expand equally and together. As the result' the air gap between the contact screws g and h is maintained substantially constant, but the contact screw h is brought into engagement with the contact screw j, upon a temperature rise according to a predetermined setting of screw j, so that a circuit is now completed by way of oneof the screws or bolts a3, the contact screws h and y' and the strips lc, icl.

The heat-sensitive unit constructed in -the 5 manner described is mounted in a case Z of subthe heads ofthe screwsdS, the nut i2 and the contact screw y' and with clearance holes for screws k2 by which the porcelain base, a is retained in position. A resilient mounting is provided by tting the screws k2 with` spring` washers k3 which are disposed either below the nuts 7b4 or between the base a and the partition Z1 or in both positions. The screws k2 also pass through conducting plates Z2 which extend along the lower face of the partition Z1 and serve to receive terminal screws Z3. y n

yIn order to permit of the setting of the contact screw i so that 'the detector may become operative when a slow rise in temperature exceeds a determined limit, the screw is provided with a pointer 7'1 to operate over a graduated disc 7'2 adapted to t around the screw i over the partition ll and -be secured in any desired position of adjustment as, for example, may be determined during manufacture for the purpose of compensating variations of setting or otherwise. By the setting of the pointer to a particular temperature indicated upon the dial and thus effecting the rotation of the contact screw j, the normal air gap between the contact screws y and h is varied accordingly.

The inner contacts and the inner element c are advantageously protected against dust by a channel section screen m tting loosely over the element c and provided with an opening through which the contact screw g may extend. The casing is advantageously closed by means of a gridlike cover Z4 permitting free access of the atmos phere to the elements b, c. c

In the operation of the detector a sudden rise of temperature causes the element b to expand more rapidly than the element c in View of the lagging of the latter, and a circuit is therefore closed between the contact screws g and h. During a long and gradual rise in temperature, such as is due to seasonal change, the elements b, c

expand together and approximately nochange takes place in the air gap between the contact screws g `and h so that the device remains still sensitive to a sudden rise of temperature which is eiective.- to cause further expansion of the element b. Should, however, the temperature exceed the limit as determined by the setting of the contact screw :i the device becomes operative by the engagement of the screws h and y'. In an installation involving the use of four of the detectors as shown in Figure 6, the detectors n are connected in parallel to the secondary of a mains transformer o and their circuits are completed through relay coils p respectively controlling indicating-lampsA pL-the circuit being cornpleted through a relay coil p2 which is effective to ope-rate an audible signal such as a bell q and a relay q1 serving to close the main circuit for the motor of a siren q2. The relay circuits are also supplied from the secondarysideof the mains transformer o which is effective also to supply current to a relay r adapted in the event of failure ofthe mains supply to close a local circuit .through a battery r1 and signal or alarm bell r2. l It will be understood that the invention is not limited to the details oi construction hereinbefore described, nor to the application o the device foruse as a lire detector. It may be applied merely for the purpose of controlling temperature conditions, for example, in refrigerators, stores and other" situations where the maintenance of determined temperature conditions are desirable or essential. n n l I claim: l. A thermal switch, particularly for usein automatic temperature change alarm devices, wherein provision is made Afor establislfling` an electric alarm circuit upon either a sudden'ternperature change of a predetermined amountor a slow continued temperature change, comprising ari linsulating fbase', projecting seats at the ends of said base, two .thermal yelements of the same `mass :and material, Vsupported at their ends on said .projecting seats-and bridging said base, insulation lagging on one lofsaid thermal elements, electrical contacts `.carried :by .and moving with said .thermal elements, and a .contact of fixed location, whereby kupcrn a rapid temperature rise differential distortion of the two thermal elements operates to establish .an alarm .circuit through one pair of :contacts and yupon a slow temperature rise substantially uniform distortion of the .two thermal elements operates to establish'an alarm circuit through a second pair of contacts.

.2. A thermal switch, particularly for use 1n 'automatic temperature change alarm devices, wherein Vprovision :is made for establishing an electric alarm circuit 'upon either a sudden temperature change of :a predetermined amount or a lslow continued temperature change, comprising an insulating base, yprojecting seats at the endof said base, two differential thermal elements supported at their ends on said projecting seats and bridging said base, contacts carried by and moving with said thermal elements, and a contact of fixed location, vall of said contacts being in alinement, whereby upon a rapid temperature rise differential distortion of the two thermal elements operates :to establish an alarm circuit through one pair of contacts and upon a slow temperature rise substantially uniform distortion of the two thermal elements operates to establish an alarm circuit through a second pair of contacts.

3. A thermal switch, particularly for use in automatic temperature change alarm devices, wherein provision is made for establishing an electric alarm circuit upon either a sudden ternperature change of a predetermined amount or a slow continued temperature change, comprising an insulating base, projecting seats at the ends of said base, two thermal elements of the same mass and material, supported at their ends on said projecting seats and bridging said base, insulation lagging on one of said thermal elements, electrical contacts carried by and moving with said thermal elements, and a contact of fixed location, whereby upon a rapid temperature rise differential distortion of the two thermal elements operates to establish an alarm 'circuit through one pair of contacts and upon a slow temperature rise substantially uniform distortion of the two thermal elements operates to establish an alarm circuit through a. second pair of contacts, all of said contacts being in alinement.

4. A thermal switch, particularly for use in automatic temperature change alarm devices, wherein provision is made for establishing an electric alarm circuit upon either a sudden temperature change of a predetermined amount or a slow continued temperature change, comprising an insulating base, projecting seats at the end of said base, two differential thermal elements supported at their ends on said projecting seats and bridging said base, contacts carried by and moving with said thermal elements, a contact of fixed location and means for adjusting the gap between cooperating contacts, whereby upon a rapid temperature rise differential distortion of the two thermal elements operates to establish an alarm circuit through one pair of contacts and upon a slow temperature rise substantially uniform distortion of the two thermal elements operates to establish an alarm circuit through a second pair yof contacts.

5. A thermal switch, particularly for use in automatic temperature `change alarm devices, wherein provision yis made for establishing an electric alarm circuit upon either a. sudden temperature change of a predetermined amount or a slow continued temperature change, comprising an insulating base, a rigid .frame lcontaining said base, a resilient mounting between said frame and said base, projecting seats at the end of said base, two differential 'thermal elements supported at `the ends on said projecting seats and bridging said base, contacts .carried by and moving with said thermal elements, and a contact of fixed location, whereby upon va rapid temperature rise differential distortion of the two thermal elements operates t0 establish an alarm circuit through one pair of contacts and upon a slow temperature rise substantially uniform distortion of the two thermal elements operates to establish an alarm circuit through a second pair of contacts.

6. A thermal switch, particularly for use in automatic temperature change alarm devices, wherein provision is made for establishing an electric alarm circuit -upon either a sudden temperature change of a predetermined amount or a slow continued .temperature change, compris- -ing an insulating base, projecting seats .at the end of said base, two differential thermal elements supported one above the other at their ends on said projecting seats and bridging said base, contacts carried by and moving with said thermal elements, a contact of fixed location, and spacing elements separating said thermal elements and made of material having substantially the same coefficient of expansion as said moving contacts.

7. A thermal switch, particularly for use in automatic temperature change alarm devices, wherein provision is made for establishing an electric alarm circuit upon either a sudden temperature change of a predetermined amount or a slow continued temperature change, comprising an insulating base, inwardly inclined projecting seats at the ends of said base, two differential thermal elements supported at the ends on said projecting seats and bridging said base, contacts carried by and moving with said thermal elements and a contact of fixed location.

8. A thermal switch, particularly for use in automatic temperature change alarm devices, wherein provision is made for establishing an electric alarm circuit upon either a sudden temperature change of a predetermined amount or a slow continued temperature change, comprising an insulating base, inwardly inclined projecting seats at the ends of said base, two differential thermal elements supported one above the other at their ends on said projecting seats and bridging said base, contacts located between, carried by and moving with said thermal elements and a contact of fixed location.

9. A thermal switch, particularly for use in automatic temperature change alarm devices, wherein provision is made for establishing an electric alarm circuit upon either a sudden temperature change of a predetermined amount or a slow continued temperature change, comprising an insulating base, inwardly inclined projecting seats at the ends of said base, two differential thermal elements supported one above the other at their ends on said projecting seats and bridglill) ing said base, contacts located between, carried by and moving with said thermal elements, a contact of fixed location, and projecting sleeves enclosing said contacts.

10. A thermal switch, particularly for use in automatic temperature change alarm devices, wherein provision is made for establishing an electric alarm circuit upon either a sudden temperature change of a predetermined amount or a slow continued temperature change, comprising an insulating base, projecting seats at the ends o1 said base, two differential thermal elements supported at their ends on said projecting seats and bridging said base, and secured to said base by means forming part of the circuit to be closed through contacts carried by them, contacts carried by and moving with said thermal elements and a contact of fixed location.

11. A thermal switch particularly for use in automatic temperature change alarm devices wherein provision is made for establishing an electricalarm circuit upon either a sudden temperature change of a predetermined amount or a slow continued temperature change, comprising a frame, an insulating base carried by said frame, projecting seats at Vthe ends of said base, two thermal elements of the same mass and material, supported at their ends on said projecting seats arranged one above the other and bridging said base, insulation lagging on one of said thermal elements, electrical contacts carried by and moving with said thermal elements, a contact of fixed location, and sleeves enclosing all said contacts, whereby differential distortion of the two thermal elements operates to establish an alarm circuit through one pair of contacts and upon a slow temperature rise substantially uniform distortion of the two thermal elements operates to establish an alarm circuit through a second pair of contacts. c

12. A thermal switch, particularly for use in automatic temperature change alarm devices, wherein provision is made for establishing an electric alarm circuit upon either a sudden temperature change of a predetermined amount or a slow continued temperature change, comprising an insulating base, two differential thermal elements arranged one above the other bridging said base, contacts located between and carried by said thermal elements, a third contact extending from one of said thermal elements, and a xed contact with which said third contact cooperates, whereby upon a rapid temperature rise diierential distortion of the two thermal elements operates to establish an alarm circuitthrough one pair of contacts and upon a slow temperature rise substantially uniform distortion of the two thermal elements operates to establish an alarm circuit through a second pair of contacts.

CECIL HERBERT STAVE.

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