US2589869A - Temperature change responsive means for controlling electric circuits - Google Patents

Temperature change responsive means for controlling electric circuits Download PDF

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Publication number
US2589869A
US2589869A US122887A US12288749A US2589869A US 2589869 A US2589869 A US 2589869A US 122887 A US122887 A US 122887A US 12288749 A US12288749 A US 12288749A US 2589869 A US2589869 A US 2589869A
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switch
circuit
source
contact
relay
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Ruffle William Harry
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SPEED DEV Co Ltd
SPEED DEVELOPMENT Co Ltd
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SPEED DEV Co Ltd
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    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B17/00—Fire alarms; Alarms responsive to explosion
    • G08B17/06—Electric actuation of the alarm, e.g. using a thermally-operated switch

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  • This invention relates to a relay-embodyingcircuit with one or more highly sensitive or millivolt type switches for afiording a warning or alternatively controlling appropriate apparatus upon a change in ambient temperature at a control zone, and in which devices such as e. g. thermo-couples which are very sensitive to changes in ambient temperature are connected to the electrically energised operating element of the switch, e. g. a coil of a switch constructed after the fashion of a milli-vclt meter, is adapted to actuate the switch so as to change from a normal or inoperative position to an operative position so as to bring into circuit relays.
  • devices such as e. g. thermo-couples which are very sensitive to changes in ambient temperature are connected to the electrically energised operating element of the switch, e. g. a coil of a switch constructed after the fashion of a milli-vclt meter, is adapted to actuate the switch so as to change from a normal or in
  • control circuits embodying a highly sensitive switch e. g. a switch constructed after the fashion of a milli-volt meter and which is operated by energising the sensitive coil therein
  • the switch is found to be unreliable in operation.
  • the direction of flow of current from the normal source through the hair spring of the switch can be such as to implement the current generated by the thermocouple, so that the switch might perform satisfactory for one switch stage in the operation.
  • one object of the present invention is to provide a circuit which obviates the foregoing disadvantage and ensures a positive holding of the moving contact against both of the co-operating contacts in the proper sequence, whereby the apparatus can be adopted with confidence as to its reliability for producing signals or controlling apparatus under conditions demanding great efiiciency, e. g. on aircraft for giving warnings of the outbreak of fire and/or for the remote controlling automatically of suitable apparatus such as e. g. heaters, coolers and fire extinguishers.
  • Another object of the present invention is to combine with the apparatus a test circuit whereby when the apparatus is used with a plurality of control points, e. g. as with the power units of aircraft, by operation of a signal switch on instantaneous indication of the effectiveness of the circuits appropriate to all of the control points' is obtained.
  • the present invention is characterised broadly in that means is provided whereby when an E. M. F. is developed at the device which is very sensitive to temperature changes, e. g. a thermo-couple, to actuate the switch, upon the moving member of the switch reaching its terminal or contact engaging position there is introduced an implemented E. M. F. which adds effectively to the output of the said very sensitive device, and when the output of the said very sensitive device falls so that it cannot overcome the influence of the means tending to return the contact to its original position when the moving contact reaches the terminal return position, an implemented E. M. F. is introduced in the reverse direction to that generated by the said very sensitive device to still further reduce the resistance to the re-assertion of the aforesaid means which returns the contact to its said original position.
  • an E. M. F. is developed at the device which is very sensitive to temperature changes, e. g. a thermo-couple, to actuate the switch, upon the moving member of the switch reaching its terminal or contact engaging position there is introduced an implemented E
  • Figure 1 is a diagrammatic view showing the invention as adapted for use with a single control source.
  • Figure 2 is a diagrammatic view showing the invention as adapted for use with a plurality of control sources
  • Figure 3 is a sectional elevation of a suitable form of thermo-couple device for use with the present invention.
  • control source C. S. from which a warning or other signal is to be derived is shown as embodying a plurality of thermo-couples arranged in series, that is to say a chain of pairs of thermo-couples 5a, 51), although of course only one pair of thermocouples may be employed where a simple single control source is contemplated.
  • the chain of thermo-couples illustrated can be assumed as being assembled at various vulnerable points on an aircraft engine.
  • thermo-couple devices are of identical form throughout, each device having its pair of thermo-couples 5a, 5b both exposed to the infiuence of normal ambient air conditions but one (5b) being shrouded by shroud 5 and the other (5a) clear of the shroud, or more fully exposed, so that the latter will be affected first by the effect of a very sudden change in temperature, e. g.
  • thermo-couples are self-compensating at a normal or gradual rise of temperature and consequently under these conditions the output of one thermo-couple a cancels out the output of its mate 5b.
  • thermocouple Ea In the event of flame, or an abnormal temperature rise, impinging on the exposed thermocouple Ea, the output of this thermo-couple will exceed that of the other, and the resultant E. M. F. i. e. the amount by which the exposed thermocouple P. D. exceeds that of the other is applied to the moving coil l of a milli-volt switch i.
  • the switch l is of the highly sensitive type, c. g. constructed as shown after the fashion of a moving coil milli-volt meter, in which the mo"- ing contact is a needle held in engagement with a fixed contact 3 by a hair spring 1.
  • the said relay means comprises a double wound relay L having a winding 8 and an oppositely Wound winding the winding 8 being connected by l ad iii to the fixed contact 5 and to the negative or return to source S by lead H, the positive connection to the winding 8 being via lead Iii, contact 8, needle contact 2, resistor R lead so closed contacts is, Eli, lead 9:: and main lead 9 to the positive of source S via resistor R this circuit including a pair of contacts so which are regularly intermittently opened and closed to introduce a pulsating supply to the needle contact 2.
  • thermo-couples upon the contact 2 moving over into engagement with contact G, and the winding 3 being energised from the source S, a of holding contacts i2 and I3 associated with this winding are closed to trans fer the electrical load from the contacts 2 and 5 to a holding circuit.
  • the said holding circuit comprises lead 30; ,4
  • Warning lamp L is brought into circuit by reason or" the closing of a pair of contacts El and 22 operated in unison with contacts !2 and t2, the contact 2
  • the contact pre. .ure is exceedingly light, hence as aioresaid, it is desirable to obtain a very positive engagement of the moving needle 2, with each of the contacts 3 and 5 the moment of contact, and for this purpose -le present invention provides means to implement the electrical energy overcoming the influence of the hair spring :2 at the moment when the contact 6 is engaged, and, in the reverse direction, to reduce the E. M. F. opposing the influence of the hair spring, so that in ei fect an assisting E. M. F.
  • E. M. F. is obtained from the source S by the introduction of the aforesaid r'sistcr R in the operating circuit which resistor, assuming we are dealing with a 24 volt source S, can have a value of 8 ohms, and can be fixed as shown in Figure 1, or may be variable as shown in Figure 2.
  • thermo-couple circuit from the normal supply source S
  • the lead 9 from the normal supply source S is taken to one side of the thermo-couple chain, the resistance R being in series with the lead 9 from the normal source and the moving contact, and in parallel with the thermo-couple chain circuit and the coil 7 of the switch, 1. e. a series-parallel connection.
  • the said holding circuit is isolated from the pulsating circuit whereby a constant warning light is given.
  • the lamp circuit canbe broken intermittently via subsidiary contacts on the pulsating relay.
  • a resistor R Connected across the said winding 8 of the double wound relay L is a resistor R adapted to reduce the current flow through the winding 8 in preparation for completing the circuit necessary for the requirements of a subsequent release circuit
  • This said winding 8 of the double wound relay L is effective for performing both functions of operating the relay and transferring the electrical load from the switch contacts 2 and 5 to the holding circuit aforesaid.
  • the value of the resistor R in relation to the circuit as a whole is such that only a potential of say six volts is applied to the winding 8 to hold it, the remaining volts said eighteen volts of a twenty four volt supply, being developed across a limiting resistance R in the main feed 9.
  • thermo-couple output is reduced to the normal state, i. e. the state appropriate to the moving contact 2 of the switch into engagement with the contact 3 aforesaid, as e. g. when the flame previously causing the low E. F.
  • the moving contact 2 of the switch is now at a potential of, taking the aforesaid example of a 24 volt source S, eighteen volts with respect to positive of the source S, and, as the aforesaid holding winding 8 of the double wound relay L has only six volts across it, the eighteen volts supplied in the reverse direction to the other winding I d of this relay L must cause the relay L to release, the release of the said relay L breaking first the holding contacts l2 and I3, as well as the lamp contacts 2
  • the contact springs of the double wound relay L are so adjusted as to open contacts !2, 13, 2
  • the moving contact 2 and contact 6 of the switch I during the initial operating period, and as that during the other or release" period, the release winding [4 of the double wound relay L is connected to positive by lead [1, and the moving contact 2 of the meter switch is now at eighteen volts negative with respect to this positive due to the volts developed across the resistor R by virtue of it being in series with winding 8 and resistor R in parallel, it will be understood that the E. M. F. in-
  • the means for constantly intermittently making and breaking the circuit to the contact 2 and lead It! to the relay 8 comprises the pulse circuit containing the relays L L and L this pulse circuit interrupting at regular and frequent intervals the operating supply in lead 9.1: via contacts 9a to the aforesaid double wound relay L during operating and release stages to prevent misoperation of the switch due to vibration.
  • the pulsating relays L L and L are connected across the twenty four volt D. C. supply via resistors R which can have a value of 2200 ohms each, the current being supplied from the continuous supply side of the lead 9 via a lead 911 to coil of relay L via 9e, resistor R to negative.
  • resistors R which can have a value of 2200 ohms each, the current being supplied from the continuous supply side of the lead 9 via a lead 911 to coil of relay L via 9e, resistor R to negative.
  • relay L contacts I are closed and the supply goes from 9d via contacts Z lead 9 coil of relay L resistor R to negative.
  • relay L opens contacts I which removes the short circuit from the coil of L L operates via lead 9d coil of L lead lift to resistor R
  • the operation of L closes contacts I which places a short circuit across the coil L which causes L to release, which in turn opens 1 contacts, thereby releasing L to close contacts I which short circuits coil L- to release it and open contacts 1 to remove the short circuit from L which then re-operates and the sequence is repeated.
  • test button 18 is for the purpose of obtaining a ready indication that the apparatus is in working order, this test button being provided in association with a relay L the energising of which relay via lead ll, button contacts l8a, 13b and lead 3i following depression of the button l8, opens contacts l9 and 20 and removes a short circuit from a resistance R in series with the thermo-couple and coil 1 circuit.
  • point 1 of the resistor R is connected to the negative supply (lead H) via lead Ila through resistor R which can be of 9100 ohms, and the other end of resistor R is connected via 9x, contacts 9a lead 93 resistor R to positive.
  • This introduction of the said E. M. F. in the thermocouple chain and consequent excitation of coil 1 will cause the contact 2 to engage contact 6, and as already indicated, this will result in contacts l2 and [3 being closed and the transfer of the load to lead l3a and return lead I l, and the contacts 2
  • a multiple-plug connector (plugs 23 and sockets 24) is provided for connecting up the relay apparatus to the warning lamp circuit and the supply source S, and the lamp unit can be plugged in by plug contacts 33 and 34.
  • the single warning lamp L and switch I When the apparatus is to be adapted to a plurality of control points, the single warning lamp L and switch I will be substituted by a number of lamps and switches l and double wound relays L with associated circuits corresponding to the number of control sources.
  • four control sources are shown, e. g. two port and two starboard aircraft engines.
  • the same number of relays L L and L will still obtain, and each of these relays will actuate its own pair of contacts 9a to cover three of the switch circuits, the fourth switch circuit being satisfied simply by adding to one of the relays, e. g. the relay L in Figure 2, a further pair of contacts 9A.
  • thermo-couple chains of the two engines on the port side to two of the circuits, and a like arrangement 2'!
  • test button [8 In addition to operating the auxiliary relay L to introduce the equivalent P. D. into the thermocouple chain, the test button [8 also removes the supply from the release windings M of the aforesaid double wound relays L to obviate their functioning and giving a false clear signal due to the engagement of the moving contact 2 and contact 3 of each of the milli-volt switches l during the break period of the pulse current introduced as a substitute for thermo-couple output.
  • thermo-couple shown in Figure 3 is preferably adopted in the thermo-couple chain.
  • Each thermo-couple comprises two lengths of wire 5! and 42 attached at one end to an insulating base disc 43 and having connected across their other ends at points it and 45 a dissimilar wire element 46 to provide two spaced points or Zones of generation of low E. M. F. Shrouding this arrangement of wires is a cylindrical metallic sleeve 41 integral with a hollow cylindrical cap 48 accommodating the insulating base disc 43 and a cover disc 49 also of insulating material, a base plate 50 being secured to a flange 51 of the cap t8 by screws 52.
  • the elements 46, 45 and can be arranged as two chromel-alumel thermo-couples in opposition so that with normal slow temperature variations little voltage output is obtained. With any rapid rise of temperature however, as in the case of a fire, the outer exposed thermo-couple becomes hotter than the inner protected one, and the voltage generated operates the appropriate moving coil relay to give a warning. When this rapid rate of rise ceases the diiference in temperature between the inner and outer thernio-couples decreases, and the warning is cancelled.
  • the cap 48 is slotted or otherwise suitably apertured as at 53 for the free access of ambient air or gas to the assembly or" wire elements, the upper point 45 of the thermo-couple device being exposed above or close to the rim of the sleeve 41 but protected from injury by upstanding lugs 54 of such sleeve.
  • Threaded upon the wire elements 32 and s5 is a disc 55 of insulating material having a clearance from the sleeve il forming a screen between the points 44 and 35. Hence, the point 45 is more exposed than the point 44 to the direct influence of flame in the vicinity of the device. 1
  • slotted cap 48 freely admits ambient air or gas to the interior of the sleeve 41 so that normally the points of the thermo-couple device are exposed to the same temperature condition, such slotted cap will act as a muiiie to prevent access of flame through the slot 53, so it is immaterial in which direction the flame plays upon the device in order to ensure that the point 45 will be subjected to the influence of the flame in advance of the point is in order to obtain the desired momentary distinctiveness in temperature at the points M and $5.
  • a milli-volt switch with a normal conditions contact, an operative circuit contact and a moving contact, means responsive to sudden temperature change to develop a very low E. M. F. of a few'milli-volts and connected to said switch to actuate the moving contact, an electrically operated appliance adapted to be actuated from an operative source of electrical energy having a much greater E. M. F. output than the said means, electrically operated means normally isolated from the switch but adapted to connect said appliance to said source and adapted to be fed from said source, means controlled by the actuation of said switch due to sudden temperature change to effectively connect said electrically operated means momentarily via said switch moving contact to said higher E. M. F. source and thereupon to isolate said moving contact from said higher E. M.
  • thermocouple for location in said source so as to generate a low E. M. F. output
  • a switch having a fixed normal conditions contact and a fixed operative circuit contact and also a co-operating moving contact actuated by said low E. M. F. output of the thermo-couple
  • a relay means to connect said relay to a normal source of .supply of electrical energy via said moving contact and said operative fixed contact so as to energise said relay when the said low E. M. F.
  • a holding circuit connected to said relay and adapted'to be fed from the normal source, a warning device or other suitable electrically operated appliance in said holding circuit, means actuated by said relay to bring in said holding circuit and cut out said switch so that the said relay is thereupon energised via the holding circuit, a pulsating circuit fed from said normal source and located in the connection from the normal source to said moving contact and operating independently of the holding circuit, a resistance in series parallel with the circuit of the thermo-couple and switch and located in the connection from said normal source to said moving contact which splits the resultant E. M. F. so that part of the E. M. F. flows through said resistance and part through the moving contact actuating means to implement the E.
  • an electrically operated appliance adapted to be actuated from an operative source of electrical energy having a much greater E. M. F. output than the said means, a holding circuit for the appliance normally isolated from the operative source of electrical energy and said switch, a double wound relay having one winding controlled by the actuation of said switch due to sudden temperature change to efiectively connect said electrically operated appliance to said higher E. M. F.
  • a pulsating relay regularly interrupting the current supply to the switch, a resistor in parallel with said low E. M. F. producing means connected to the switch and in series with said operative source and the switch to produce splitting of the resultant E. M. F. developed across the said resistor so that part flows through the resistor and part through said low E. M. F. producing means to feed from said higher E. M. F. source an assisting E. M. F. into the switch actuating means when the switch is actuated to bring in the said appliance, a resistor connected across said winding adapted to reduce the current fiow through the winding, a release circuit adapted to feed an assisting E. M. F.
  • a milli-volt switch means responsive to sudden temperature change to produce a very low E. M. F. of a few milli-volts and connected to said switch to actuate the switch, an electrically operated appliance adapted to be actuated from an operative source of electrical energy having a much greater E. M. F. output than the said means, a holding circuit for the appliance normally isolated from the operative source of electrical energy and said switch, a double wound relay controlled via one of its windings by the actuation of said switch due to sudden temperature change to'effectively connect said electrically operated appliance to said higher E. M. F. source whilst transferring the load due to said source from said switch to said holding circuit, means to feed from said higher E. M. F. source an assisting E.
  • thermocouples adapted to be located at a plurality of independent possible fire outbreak sources and connected to said switches to actuate one of the switches upon a sudden temperature rise at one of said sources, an electrically operated warning device common to all of said switches adapted to be connected to and actuated from a normal operative source of electrical energy common to all of said switches and having a much greater E. M. F.
  • thermo-couples a double wound relay and a holding circuit with each switch, said double wound relay being adapted to connect via one of its windings said warning device to said operative source and being adapted to be fed from said operative source, means controlled by the actuation of each switch due to sudden temperature change to effectively connect the said winding of the associated said double wound relay momentarily via the associated 11 switch moving contact tovv said higher E. M. F. source and thereupon to isolate said moving contact from said higher E. M. F. source and maintain the said holding circuit in operation means to feed from said higher E. M. F. source an implementing E. M. F. into the means actuating the switch when the switch is actuated to bring in.
  • the said warning device the other winding of the double wound relay being connected to said operative source and the switch so as to receive a greater E. M. F. than the first mentioned winding so as to override the first mentioned winding to break the. holding circuit when the switch is returned to normal, and means feeding an assisting E. M. F. into the switch actuating means when the. second mentioned winding is brought into circuit.
  • A. fire warning apparatus including an auxiliary thermo-couple set to respond to gradual changes in temperature and in series connection with other thermo-couples which respond only to a sudden rise in temperature.
  • Electrically operated apparatus for bringing into operation in response to a. predetermined change in temperature at a remote source a warning device or other electrically operated appliance, comprising an operation initiating circuit, a. highly sensitive switch in said circuit and also means adapted to be positioned at said remote source and susceptible to the influence of a predetermined form of change in ambient temperature at said remote source so as to change the electrical characteristics of said initiating circuit to actuate the switch, a main holding circuit adapted to be connected to an available normal source of electrical energy and to be closed via said switch consequent upon a. predetermined change in said ambient temperature for maintaining the operation of the warning device or other appliance. independently of theoperation initiating circuit, means actuated consequent upon closing.
  • said switch has a moving contact of very light form and anactuating coil and a. hair spring similar to a milli-volt meter, and a normal conditions contact anda holding circuit contact, the coil being connected to the output of the means adapted to change the characteristics of the operation initiating circuit, and the moving contact being connected to the holding circuit via the hair spring.
  • the switch has two fixed contacts which are engaged alternately by a moving contact of very light form actuatedby the low E. M. F. developed due to temperature change at the remote source, said fixed contacts being connected. to a double would relay having two oppositely wound windings, one of these windings operatin contacts to bring in the holding circuit and being connected across the fixed contact which brings in the hold- 12 ingcircuit when engaged by the moving contact and a return lead or" the normal electrical energy supply source, the moving contact being connected to the positive or supply lead of said normal source, the other winding of the double wound relay acting as a release winding and actuating a pair of contacts via which it is connected at one end to the other or release fixed contact of the switch its other end being connected to positive of the normal supply, the contacts of the first mentioned winding breaking inadvance of the contacts of the second mentioned winding when the switch is returned to normal, said release fixed contact being connected via the moving switch contact via a lead including a resistor in parallel with the switch
  • thermo-couple device with two coupled points Or zones of generation of low E. M. F- one or which is so shrouded that whilst during gradual ambient temperature changes they respond identically and cancel each other out, there is an advance in the response of the unshrouded point or zone. relative to the shrouded one when there is a very pronounced sudden change in the ambient temperature, e. g. upon the outbreak of fire in close proximity to the device, to cause. a development of a low E. M. F. sufficient'to actuate the switch.
  • a milli-volt switch comprising two fixed contacts, a. very light swinging pointer contact adapted to engage alternately the fixed contacts, a hair spring to actuate said swinging contact in one direction, a moving coil adapted to actuate the swinging contact. in. the other direction, means responsive to sudden temperature change to produce a very low E. M. F. of a few milli-volts and connected to said coil of theswitch to actuate the SWltCh,.'a, holding circuit, an electrically operated appliance. in said holding circuit adapted to be actuated from an operative source of electrical energy having. a much greater E. M. F. output than the said means, said holding circuit being normally isolated from its operative source of electrical energy and from said.
  • switch means controlled by the, actuation of said. switch due to very sudden temperature change. to close said holding, circuit and eifectively connect said electrically operated appliance to-said higher E. M. F. source whilst transferring the. load due to said sourcefrom said switch to said holding circuit, means to feed from said higherv F. source an assisting E. M. F. into thesaid coilof the switch when the-swinging contact engages one of said fixed contacts to bring in the said appliance and when it' engages the other fixed contact to cut out said appliance, and
  • a mulli-volt switch an operation initiating circuit including said switch, means to develop a very low change in E. M. F. of a few milli-volts in said circuit to actuate the switch, said switch embodying two fixed contacts and a very light swinging contact adapted to alternately engage the fixed contacts, a hair spring to actuate said swinging contact in one direction, a moving coil adapted to actuate the swinging contact in the other direction against the influence of said hair spring, electrically operated apparatus, a main circuit to connect said apparatus via said switch to a main source of E. M. F. having a much greater E. M. F. than the E. M. F. feeding the operation initiating circuit, means to introduce an assisting E. M. F.
  • thermo-couple chain including a number of thermo-eouple devices each having a pair of thermo-couples both exposed to the influence of normal ambient air conditions but having one more exposed than the other so that it will be affected first by the efiect of a very sudden change in ambient temperature, a switch having two fixed contacts (normal and main respectively), a very light moving contact to alternately engage the fixed contacts, a hair spring actuating the moving contact in one direction, a moving coil connected in series with said thermo-couple chain so that it is energised to operate the moving contact in the opposite direction against the influence of said hair spring by the very low M.
  • a relay a main circuit adapted to be connected by said relay via said switch to a main source of E. M. F. when said coil is energised to move the moving contact into engagement with said main contact, means to isolate the switch from the main circuit immediately the said connection to the main source of E. M. F. has been effected by the moving and main contacts and to maintain the main circuit closed, means energised from said main source to implement the E. M. F. ob-
  • thermo-couple chain tained from the thermo-couple chain to operoverriding the aforesaid relay and breaking said main circuit.
  • thermo-couple chain including a number of thermo-couple devices each having a pair of thermo-couples both exposed to the influence of normal ambient air conditions but having one more exposed than the other so that it will be effected first by the cffeet of a very sudden change in ambient temperature, a switch having two fixed contacts (normal and main respectively), a very light moving contact to alternately engage the fixed contacts, a hair spring actuating the moving contact in one direction, a moving coil connected in series with said thermo-couple chain so that it is energised to operate the moving contact in the opposite direction against the influence of said hair spring by the very low E. M. F.
  • a relay a main circuit adapted to be connected by said relay via said switch to a main source of E. M. F. when said coil is energised to move the moving contact into engagement with said main contact, means to isolate the switch from the main circuit immediately the said connection to the main source of E. M. F. has been effected by the moving and main contacts and to maintain the main circuit closed, a resistor across said main circuit and one end of said coil and in series parallel connection with said chain, so that at the moment of engagement of the moving contact with said main contact part of the current flow due to the main source flows through the resistor and part through the thermo-couple chain to the moving coil of the switch to introduce an implementing E. M. F.
  • Electrically operated apparatus for bringing into operation by reason of a sudden change in temperature at a control source a warning or other electrically actuated device, comprising a very sensitive switch operable by an E. M. F. of a few milli-volts, means responsive to sudden temperature change to produce a very low E. M. F. of a few milli-volts and connected to said switch to actuate the switch, an electrically operated warning or other electrically operated device operated from a source of electrical energy having a much greater E. M. F. output than the said means, a holding circuit for the said device normally inoperative, means controlled by the actuation of said switch due to sudden temperature change to efiectively connect said electrically actuated device to said higher E. M. F. source whilst transferring the load due to said means controlled by the actuation of said switch from said switch to said holding circuit, and means to feed from said higher E. M. F. source an assisting E. M. F. into the switch actuating means.
  • Apparatus according to claim 17 wherein the said means responsive to sudden temperature change to produce a very low E. M. F. comprises a thermo-couple device with two coupled points or zones of generation of low E. M. F. one of which is so shrouded that whilst during gradual ambient temperature changes they respond identically and cancel each other out, there is an advance in the response of the unshrouded point or zone relative to the shrouded one when there is a very pronounced sudden change in the ambient temperature, e. g. upon the outbreak of fire in close proximity to the device, to cause a development of a low E. M. F. suiiieient to actuate the switch.
  • Apparatus according to claim 17 including said means to produce a very low E. M. F. and the switch an E. M. F. approximately equal to the output of said circuit obtaining when the switch is actuated normally by the very low E. M. F. due to the sudden rise in temperature.
  • Apparatus according to claim 17 including means which returns the said switch to normal circuit broken position when the temperature at the control source returns to below the predetermined operative temperature.

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  • General Physics & Mathematics (AREA)
  • Thermally Actuated Switches (AREA)
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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2820218A (en) * 1954-10-22 1958-01-14 Weston Electrical Instr Corp Thermally sensitive detecting arrangements
US2894251A (en) * 1954-10-18 1959-07-07 Speed Dev Company Ltd Temperature change responsive means for controlling electric circuits
US3044049A (en) * 1957-05-01 1962-07-10 Speed Developments Company Ltd Temperature alarm systems

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
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US1443165A (en) * 1923-01-23 Electric signaling and contbolling appabattts
US2127343A (en) * 1929-10-03 1938-08-16 Kellogg Switchboard & Supply Annunciator system
US2219391A (en) * 1936-08-06 1940-10-29 Mine Safety Appliances Co Combustible gas alarm and control
US2376920A (en) * 1944-06-19 1945-05-29 Edison Inc Thomas A Fire alarm system
US2473940A (en) * 1945-11-20 1949-06-21 Edison Inc Thomas A Fire alarm system

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Publication number Priority date Publication date Assignee Title
US1443165A (en) * 1923-01-23 Electric signaling and contbolling appabattts
US2127343A (en) * 1929-10-03 1938-08-16 Kellogg Switchboard & Supply Annunciator system
US2219391A (en) * 1936-08-06 1940-10-29 Mine Safety Appliances Co Combustible gas alarm and control
US2376920A (en) * 1944-06-19 1945-05-29 Edison Inc Thomas A Fire alarm system
US2473940A (en) * 1945-11-20 1949-06-21 Edison Inc Thomas A Fire alarm system

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2894251A (en) * 1954-10-18 1959-07-07 Speed Dev Company Ltd Temperature change responsive means for controlling electric circuits
US2820218A (en) * 1954-10-22 1958-01-14 Weston Electrical Instr Corp Thermally sensitive detecting arrangements
US3044049A (en) * 1957-05-01 1962-07-10 Speed Developments Company Ltd Temperature alarm systems

Also Published As

Publication number Publication date
NL152212B (nl)
FR1030561A (fr) 1953-06-15
NL77725C (nl)
DE896162C (de) 1953-11-09

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