US1925781A - Stoker timer - Google Patents

Description

Sept, 5, 1933. D, G, TAYLOR 1,925,781

STOKER TIMER Filed July 15, 193]. 4 Sheets-Sheet 1 wk I N Jwwmloz 6' 1 Daniel G. Tayloz;

D. G. TAYLOR Sept. 5, 1933.

STOKER TIMER 4 Sheets-Sheet 2 M O M u/ w i in a J m m NW D w 9%. Q Q 1 R k mww Nww M a m fi i w WM. m v Q m .& m w\ B m? w v? w D; G. TAYLOR Sept. 5, 1933.

STOKER TIMER Filed July 15, 1931 4 Sheets-Sheet 3 Q gwuentoz Daniel '6'. Ta yloz',

Sept. 5, 1933. D. G. TAYLOR 1,925,781

STOKER T'IMER Filed July 15, 1931 4 Sheets-Sheet 4 q Daniela Taylor,

Moi/weal Patented Sept. 5, 1933 STOKE]! TDIEB Daniel G. Taylor, Minneapolis, Minn, assignor to Minneapolis Honeywell Regulator Company, Minneapolis, Minn, a corporation of Delaware Application July 15, 1931. Serial No. 550,911

18 Claims. (o1. 236-1) The object of my invention is to produce a controlling mechanism operating automatically to cause the intermittent energization of an electric motor at time intervals of desired duration, the spacing and duration of said time intervals being dependent upon the automatic response of temperature-responsive elements.

The apparatus has been primarily designed for the control of an electric motor utilized to control the operation of a fuel-stoking apparatus but it will be readily understood that the apparatus may be used for other purposes and therefore the term fuel motor as used herein, is intended to apply to any electric motor which is to be intermittently energized for periods of variable duration at spaced intervals.

The accompanying drawings illustrate, diagrammatically, my invention:

Fig. 1 is a diagrammatic illustration of one form of my invention;

Fig. 2 a diagrammatic illustration of a modification of the form shown in Fig. 1;

Fig. 3 a diagrammatic illustration of a third form of my invention and,

Fig. 4 a diagrammatic illustration of a modification of the form shown in Fig. 3.

In all of the drawings S indicates what may be conveniently described as a mechanical switchactuator comprising an oscillating shaft 10 biased in one direction by any suitable means, such for instance as a weight 11 suspended by a cord 12 wrapped around and attached to the shaft. Shaft 10 carries a ratchet wheel 13 having ratchet teeth 14 and two circumferentially-spaced pins 15 and 16 arranged to engage and oscillate 'a circuitcontrolling arm 17. Wheel 13 may be driven step by step in a direction opposite to the bias produced by element 11 by a pawl 18 and may be held in its successive advanced positions by a pawl 19. Movement of arm 1'7 is limited, in opposite directions, by stops 20 and 21.

Pawl 19 may be retracted from teeth 14 by the core or armature of a,relay X having coil 26, a spring 2'7 being interposed between element 25 and pawl 19 to yieldingly urge pawl 19 into en.- gagement with teeth when element 25 is so positioned as to permit such engagement.

The temperature-responsive circuit-controlling element R. comprises a bimetallic blade having electrically-connected contact fingers 31 and 32 and a pair of fixed terminals 33 and 34 coordinated with the terminals '31 and 32 respectively, the arrangement being such that finger 32 will contact with terminal 34 before finger 31 contacts with terminal 33 and, on the oppositestroke of blade 30, finger 31 will leave terminal 33 before finger 32 is retracted from terminal 34.

Arm 1'7 is arranged to shift electric terminal 35 into and out of contact with terminal 36.

The relay X comprises a switch'3'7 with its cooperative terminal 38 and a switch 39 with cooperative terminals 40 and 41, the arrangement being such that switches 3'7 and 39 are normally out of contact with their respective terniinals 38 and 40 when pawl 19 is in position to engage teeth 14, at which time switch 39, is in contact with its terminal 41,'and the relay X is deenergized.

A transformer T comprises a primary 42 and secondary 43, the primary being permanently connected by wires 44 and 45 with the line wires 46 and 47 respectively.

The electric motorM is the motor which is to be automatically controlled, and is connected by wire 48 with line wire 46 and by wire 49 with terminal 40.

For convenience motor M will be hereafter referred to as the stoker motor.

Referring now to Figs. 1 and 2. Relay R comprises a coil 51, a .core or armature 52, switches 53 and 54 actuated by armature 52, a pair of terminals 55 and 56 which cooperate alternately with switches 53 and 54, and a link 57 which connects armature 52 with a lever 58 upon which pawl 18 is mounted, the arrangement being such that when coil 51 is energized pawl 18 will be moved to advance wheel 13 through a predetermined angle and, when the coil 51 is deenergized pawl 18 will be retracted from teeth 14. Pawl-and-ratchet mechanism of this character is so well-known that I merely illustrate it diagrammatically.

Connected with terminal 55 by wire 60 is a bimetallic blade 61 having contact fingers 62 and 63 normally out of contact with the respective fixed terminals 64 and 65 and, under response of blade 61 to increase in temperature, coming successively into contact with said terminals 64 and 65. Terminal 64 is connected by a wire 66 with line wire 4?. Terminal 65 is connected by wire 6'7 with one end of coil 51 of relay R and with switch 53, and the other end of coil 51 is connected by wire 68 with line wire 46.

Terminal 56 is connected by a wire 69 with one end of a heater coil '70 arranged in position to influence the bi-metallic blade 61, the other end of this coil being connected by a wire 71 with line wire 46. Terminal 35 is connected by wire '72 with terminal 34 and one end of the secondary 43 of transformer T. The other end of secondary 43 is connected by wire '74 with one end of coil 26 of relay X and the other end of said coil is connected by the branched wire 75 with switch arm 3'! terminal 33 and terminal 36. A wire '76 connects switch arm 39 with line wire 4'7. A wire '77 connects terminal 41 with blade 54. A wire '78 connects terminal 38 with blade 30. 1

Themechanism illustrated at the left hand end of Fig. 1 may be conveniently referred to as a thermal timer in which the circuit control switch 35-36 is automatically closed at the end of a predetermined time interval, the extent of which is dependent upon the response of the bi-metallic blade 61 to the heat conditions of coil 70 and the parts are shown in Fig. 1 in the positions attained at the end of one of these predetermined time intervals, pin 16 having driven arm 17 to a position against stop 21 where arm 1'7 has closed terminal 35 upon terminal 36 to establish the circuit 35, 72, 43, 74, 26, 75, 36, thus energizing the relay X to close switch arms 37 and 39 upon their respective terminals 38 and 40 and withdraw switch arm 39 from terminal 41, and retract pawl 19 from ratchet wheel 13., Contact between 39 and 40 establishes the circuit 47, 76, 39, 40, 49, M, 48, to start the stoker motor M. V

.When relays X and R' are deenergized blade 39 contacts with terminal 41 and blade 54 contacts with terminal 56 and, blade 61 being cold, terminals 62 and 63 are separated from their respective terminals 64 and 65. The circuit '47, 76, 39, 41, 77, 54, 56, 69, 70, 71, 46, causing a heating of coil 70 to which blade 61 responds, first contacts 62 with 64 and then 63 with 65 to close the circuit 47, 66, 64, 62, 61, 63, 65, 6'7, 51, 68, 46, thus energizing relay R to cause pawl 18 .to advance wheel 13 one step in a counter-clockwise direction, and to shift blade 54 from terminal 56', thus breaking the circuit of coil 70, and to shift blade 53 into contact with terminal 55. When 53 contacts with 55 the holding circuit 4'7, 66, 64, 62, 61, 60, 55, 53, 67, 51, 68, 46, is established so that coil 51 of relay R is kept energized until coil 70 and blade 61 cool down enough to cause 62 to separate from 64, whereupon relay R is deenergized so that pawl 18 is retracted from wheel 13. The deenergization of relay R permits 54 to contact with 56 thus re-establishing the energizing circuit for the heating coil 70 to cause blade 61 to again move to cause terminals 62 and 63 to again contact with terminals 64and 65 respectively, in the order named, and this results, as described above, in another step of advancement of wheel 13, these operations being repeated until pin 16 drives arm 17 to the position shown in Fig. 1 where said arm causes terminal 35 to contact with terminal 36, thus establishing the circuit 43, '74, 26, 75, 36, 35, 72, 43, to energize relay X and retract pawl19 from wheel 13.

The energization of relay X causes terminal 37 to contact with terminal 38 and withdraws terminal 39 from terminal 41 and contacts said terminal 39 with terminal 40, thereby establishing the circuit 47, 76, 39, 40, 49, M, 48, 46, to enerize the motor M. In due course blade 61 cools down to retract 63 and 62 from terminals 65 and 64, respectively, in the order named, thus breaking the holding circuit of relay R, and pawl 19 having previously been retracted from said wheel, weight 11 acts upon wheel 13 to drive it in a reverse direction until pin 15 contacts with arm 17 and shifts said arm over against stop 26 to permit terminal 35 to separate from terminal 36. Separation of terminal 35 from terminal 36 breaks the circuit through coil 26 so that the energizing circuit of the motor M is broken at 39--40, thus reestablishing the circuit of coil 76.

So long as the room thermostat R is sufficiently heated, i. e., is satisfied, terminals 33 and 34 are not contacted and the energizing circuit of motor M will be intermittently established and broken at regular intervals, each establishment of the circuit occurring at the end of a period which is required to advance pin 16 from its initial cold position to the position shown in Fig. 1, this time interval being dependent upon the heat-responsive period of oscillation of blade 61 and the number of required step-by-step advancements of wheel 13. The duration of actuation of the motor M, under these circumstances, will be dependent upon the time required for blade 61 to cool down, at the end of its last response to heat of coil 70, sufliciently to separate 62 from 64. This period will be determined by the design of the coil and blade 61 and will be of sufiicient duration to permit motor. M, during that period, to deliver a minimum charge of fuel to the furnace just sufficient to insure maintainance of fire in the furnace, say a period of a few minutes in each hour, more or less.

Whenever the temperature surrounding the room thermostat R drops sufficiently 32 first contacts with 34 and then 31 with 33 to establish the circuit 43, 72, 34, 32, 30, 31, 33, 75, 26, '74, 43. Relay X will be energized to retract pawl 19 from wheel 13 and blade 39 from terminal 41, and to contact blade 39 with terminal 40, thus closing the energizing circuit of motor M, and to contact blade 37 with terminal 38 to form the holding circuit 43, 72, 34, 32, 30, 78, 38, 37, 75, 26, 74, 43, for relay X so as to maintain the circuit of Motor M and the'circuit of relay X until room thermostat R is heated sufiiciently to cause retraction of 32 from 34. Retraction of pawl 19 from wheel 13 permits return of wheel 13 to initial position so that pin 16 is automatically re-positioned at its initial point ready to be started on a new advance whenever relay X is deenergized by satisfaction of the room thermostat R. So long as 32 remains in contact with 34 blade 39 will remain in contact with 40 and out of contact with 41 so that during the room thermostat R is satisfied so as to separate 32 from 34, relay X is deenergized to restore pawl 19 to cooperative relation with wheel 13 and to restore 39 in contact with 41, thereby closing the circuit of coil 70 and starting the apparatus on a new cycle.

Referring now to Fig. 3. In this construction,

instead of actuating pawl 18 by means of a relay which is responsive to a heat-responsive element, I actuate the pawl directly by a heat-responsive element. In this construction pawl 18 is advanced by a lever'80 connected by link 81, conveniently a non-conductor, with a bi-metallic blade 82 arranged to be responsive to heating coil 83, one end of which is connected by wire 84 with line 46 and the other end of which is connected by wire 85 (conveniently through blade 82) with a spring terminal 86 arranged to cooperate with a spring terminal 87 which is connected by Wire 88 with terminal 41.

Projected through a perforation 90 in blade 82 is a spring latch 91'the down-turned end 92 of that period coil 70 will not be heated. As soon as which is arranged to have a latching engagement 1 with the free end 93 of terminal 86. Latch 91 is provided with a cam 94 engaged by blade 82.

Fig. 3 shows this construction in an intermediate position where blade 82 is moving to the right under the effect of heat in coil 83, pawl 18 advancing wheel 13 and just about in position to be automaticaly retracted from teeth 14. Finger 92, lying behind terminal 86, holds said terminal stressed to the left in contact with terminal 87, which establishes the circuit 47, 76, 39, 41, 88, 87, 86, 82, 85, 83, 84, 46. As blade 82 moves further to the right it rides across cam 94 to permit finger 92 to move upwardly away from' end 93, thus permitting terminal 86' to spring to the right and end 93 of terminal 86 so as to hold terminal 86 against movement to the left. Further cooling of blade 82 swings the free end of said blade to the left end the blade rides over cam 94, thus stressing spring terminal 86 and giving it a bias towards the-left. When blade 82 rides to the left it stresses terminal 86 to give said terminal a bias towards the left, said terminal being restrained by finger 92 until blade 82 passes to the left beyond cam 94, whereupon finger 92 is retracted upwardly from end 93 of terminal 86 and said terminal is permitted to spring to the left to contact with terminal 87, thus again closing the circuit of heater coil 83. The automatic heat-responsive reciprocations of blade 82 serve to advance wheel 13 step-by-step until arm 17 is stopped by stop pin 21, said arm at that moment closing 35 upon 36, thus closing the circuit of relay X in the manner already described.

It is thought to be unnecessary to repeat at this point a description of the energization and de-energization of motor M.

Referring now to Figs. 2 and 4.

The time-cycle of the device shown in Fig. 1 will be a function of blade 61 and coil and, likewise, the time-cycle of the construction shown in Fig. 3 will be a function of blade 82 and coil 83. The heat-response period of these devices will be dependent upon design or adjustment of the coil and/or blade and may be varied through a wide range by proper design.

It is desirable, at times, to be able to modify the time-cycle without adjusting or modifying the blade or coil and for this purpose I provide the arrangement diagrammatically illustrated in Figs. 2 and 4 by the interposition of a bi-metallic heat-responsive blade 95 connected by wire 96 with wire 78, Blade 95, when eold, contacts with a terminal 97 connected by wire 98 with wire 72, and is retracted from terminal 97 by response to heat in a coil 99, one end of which connected by wire 100 with wire 49, and the other end of which is connected by wire 101 with wire 48, that is to say, coil 99 is bridged across the terminals of motor M.

Upon energization of motor M, either by the action of the temperature-responsive timer or the room thermostat, a circuit 46, 48, 101, 99, 100, 49, 40, 39, 76, 47, heats coil 99 and causes a retraction of blade 95 from terminal,97. An energization of relay X,.either in responsive to action of the heat-responsive timer or action of the room thermostat R, having closed 37 upon 38, the circuit 43, 72, 98, 97, 95, 96, 78, 38, 37, 75, 26, 74, 43, will be maintained until it is broken at 95-97 in response to the heat condition of coil 99 and consequently the motor M having once been energized, either by the action of the room thermostat or the heat-responsive timer, will continue in operation for the period of time at least as long as that determined by the response of blade 95 to the heating coil 97. If relay X has been energized by action of the room thermostat R, and 95 separates from 9'7 before 32 separates from 34, the motor M will continue in operation until 32 separates from 34, because the circuit 43, 72, 34, 32, 30, 78, 38, 37, 75, 26, 74, 43 will keep relay X energized and 39 in contact with 40 until 32 separates from 34. I Terms used in the claims are defined as follows:

Step-by-step actuator, a switch-actuating mechanism, such as the assembly S, movable by an element a portion of which moves to predetersuccessive steps from an initial position to a switch-actuating position; releaser", means normally holding the step-by-step mechanism in its successive advanced positions which, when withdrawn, permits or causes a return of the step-by-step mechanism to initial position; room thermosta a circuit-controlling element responsive to its ambient medium to vary electrical circuits; temperature-responsive element,

mined positions dependent upon the temperature of the element.

I claim as my invention: I

1. A control device comprising an energizing circuit for an electric'motor to be controlled, a relay embodying a switch in said circuit and a second switch, a third switch, a step-by-step actuator biased to initial position and. capable of shifting said'third switch at opposite ends of the cycle of said actuator, a detent normally restraining said actuator against its bias and controlled by said relay, a room thermostat, energizing circuits for said relay embodying said third switch and the room thermostat, a temperature-responsive element controlling forwarding actuation of the step-by-step actuator, an electric heater arranged to affect said temperature-responsive element, and an energizing circuit for cyclically heating said heater embodying the second switch controlled by the relay.

2. A control device comprising a step-by-step switch actuator biased to initial position, a temperature-responsive element, means controlled by said temperature-responsive element for in termittently forwarding said step-by-step actuator, an electric heater arranged to affect said temperature-responsive element, a releaser nor mally restraining said step-by-step actuator against its bias, an energizing circuit for said heater comprising two switches one directly actuated by the temperature-responsive element to cause intermittent heater energization and consequent movement of said switch and the other under control of the releaser, and means for, actuating said releaser.

3. A control device comprising a step-by-step switch actuator, means for causing a one-step movement of said step-by-step element to initial position, means for activating said last-mentioned means, a temperature-responsive element, means controlled by said temperature-responsive element for successively forwarding said step-bystep actuator, an electric heater arranged to affect said temperature-responsive element, and an energizing circuit for said heater comprising two switches, one directly actuated by the ternperature-responsive element to cause intermittent heater energization and consequent movement of said switch and the other under control of the return activating means.

4. A control device comprising, an energizing circuit for an electric motor, a relay embodying a switch in said circuit and a second switch, a third switch, a step-by-step actuator for said third switch and biased to initial position, a releaser normally restraining said actuator against its bias and controlled by said relay, a room thermostat, two energizing circuits for said relay one embodying said second and third switches and the other embodying the room thermostat,'145 a temperature-responsive element, a second relay .for advancing the step-by-step actuator, an energizing circuit for said second relay controlled by the temperature-responsive element, and an energizing circuit for cyclically heating 150 said heater comprising two switches one controlled by the first-mentioned relay and the other controlled by the second-mentioned relay.

5. A control device comprising a heat-responsive thermostatic blade, an electric heater for said blade, a spring terminal carried by said blade yieldingly displaceable in either direction from a medial position relative to said blade, a coacting terminal, an energizing circuit for said heater including said coacting terminals, an abutment movable into and out of position to intermittently block movement of the spring terminal with the bi-metallic blade in each direction of movement of said blade, and a connection between said abutment and blade serving to move said abutment into and ,out of terminal-blocking position by predetermined movements of the blade.

6. A control apparatus comprising a step-byst'ep actuator biased to initial position, a ratchet driver for advancing the same, a releaser normally restraining said actuator against its ,bias, a bimetallic thermally-responsive blade connected to said ratchet driver, a spring terminal car- 'ried by said blade and flexible toward and from said blade from 'a normal medial position, a second terminal coacting with the spring terminal, an electric heater for said blade, an energizing circuit for said heater embodying said coacting terminals and a switch coordinated with the releaser, and means controlled by the step-by-step actuator at the end of its forward movement for retracting the releaser and breaking the energizing circuit of the heater.

'7. A control apparatus comprising a step-bystep actuator biased to initial position, a ratchet driver for successively advancing the actuator, a releaser normally restraining said actuator against its bias, a bimetallic thermally-responsive blade connected to said ratchet driver, a spring terminal carried by said blade and flexible toward and from saidblade from a normal medial position, a second terminal co-acting with the spring terminal, an electric heater for said blade, an energizing circuit for cyclically heating said heater embodying said co-acting terminals and a switch coordinated with the releaser, a relay for manipusecond terminal co-acting with the spring termi nal, an electric heater for said blade, an energizing circuit for cyclically-heating said heater embodying said' co-acting terminals and a switch coordinated with the releaser, a relay for manipulating said releaser, an energizing circuit for said relay embodying a switch actuated by the stepby-step actuator at the extremes of its movement, and a holding circuitfor said relay embodying a switch actuated by the relay.

9. A circuit controller comprising, a relay embodying a normally-open switch to be incorporated in a circuit to be controlled, an initial energizing circuit for said relay, a holding circuit for said relay embodying a normally-open switch closed by relay energization, an element autoof the relay for restoring said actuator to initial T position to open said last-mentioned switch.

10. A circuit controller comprising, a relay embodying a normally-open switch to be incorporated in a circuit to be controlled, an initial energizing circuit for said relay, a holding circuit for said relay embodying a normally-open switch closed by relay energization', an element automatically responsive to its local conditions, circuitcontrolling elements connected to said element and embodied in said initial energizing circuit, a temperature-responsive switch in said holding circuit, an electric heater, an energizing circuit for said heater, embodying the first-mentioned switch, a switch in said relay-energizing circuit, an actuator for said switch, means for successively forwarding said actuator to switch-closing position at the end of a predetermined actuator cycle, means controlled by energization of the relay for restoring said actuator to initial position to open said last-mentioned switch, and means controlled by the relay for energizing actuator forwarding means upon restoration of the actuator to its initial and switch-opening position.

11. A circuit controller comprising, a relay, an initial energizing circuit for said relay, a holding circuit for said relay embodying a normallyopen switch closed upon relay energization, an

element automatically responsive to its local con-,

ditions, circuit-controlling elements connected to said element and embodied respectively in said initial energizing circuit and said holding circuit, a temperature-responsive switch in said holding circuit, an electric heater, an energizing circuit for said heater, a switch in said last-mentioned energizing circuit actuated by said relay and adapted to be embodied in a circuit to be controlled, a switch in said relay-energizing circuit and relay-holding circuit, an actuator for said switch, means for forwarding said actuator to switch-closing position at the end of a predetermined period, and means controlled by 'energization of the relay for restoring saidactuator to initial position to open said last-mentioned switch.

12. A circuit controller comprising, a relay, an

initial energizing circuit for said relay, a holding circuit for said relay embodying a normally-open switch closed upon relay energization, an element automatically responsive to its local conditions, circuit-controlling elements connected to said element and embodied respectively in said initial energizing circuit and said holding circuit, a temperature-responsive switch in said holding circuit, an electric heater, an energizing circuit for said heater, a switch'in said last-mentioned energizing circuit actuated by said relay and adapted to be embodied in a circuit to be controlled, a

' switch in said relay-energizing circuit and relay holding circuit, an actuator for said switch, means for forwarding said actuator to switch-closing position at the end of a predetermined period, means controlled by energization of the'relay for restoring said actuator to initial position to open said last-mentioned switch, and means controlled ing circuit for said electro-magnetic means com-.'

prising a switch, a multi-step actuator requiring a plurality of advancing steps from initial position to close said last-mentioned switch and a single-step movement to open said switch, a second elcctro-magnetic means for successively advancing said actuator toward and to switch-closing position, an energizing circuit for said second electro-magnetic means, an electro-thermal switch controlling said last-mentioned circuit,

the thermal circuit of said electro-thermal switch embodying a switch actuated by said second electro-magnetic means to cyclically control the electro-thermal switch and also embodying a switch controlled by the first-mentioned electromagnetic means and opened upon energization of said first-mentioned electro-magnetic means, and means controlled by the first-mentioned electro-magnetic means for moving the actuator to initial position and thereby opening the second-mentioned switch. v

14. Apparatus of the character specified in the immediately preceding claim and including switching means responsive to variations in local conditions, and an energizing circuit for said first-mentioned electro-magnetic means controlled by said switching means.

15. A controller comprising a switch biased to one position, electro-magnetic means for shifting said switch to its other position, an energizing circuit for said electro-magnetic means comprising a switch, a multi-step actuator requiring a plurality of advancing steps from initial position to close said last-mentioned switch and a single-step movement to open said switch, a second electro-magnetic means for successively advancing said actuator toward and to switch-closing position, an energizing circuit for said second electro-magnetic means, an electro-thermal switch controlling said last-mentioned circuit, the thermal circuit of said electro-thermal switch embodying a switch actuated by said second electro-magnetic means to cyclically control the electro thermal switch and also embodying a switch controlled by the first-mentioned electro-magnetic means and opened upon energization of said first-mentioned electro-magnetic means, means controlled by the first-mentioned electro-magnetic means for moving the actuator to initial position and thereby opening the second-mentioned switch, switching means respon- -sive to variations in local conditions, an energizing circuit for said first-mentioned electromagnetic means controlled .by said switching means, a heating coil connected to the dead side of the first-mentioned switch and connected with an energy source, a thermally-responsive, cold-closed switch arranged within the influence of said heating coil, and an energizing circuit for the first-mentioned electro-magnetic means including said last-mentioned thermally-responsive switch and the second-mentioned switch but excluding ,the switching means responsive to variations in local conditions.

16. A controller comprising a switch biased to one position, electro-magnetic means for shifting said switch to its other position, an energizing circuit for said electro-magnetic means comprising a switch, a multi-step actuator requiring a plurality of advancing steps from initial position to close said last-mentioned switch and a singlestep-return movement to open said switch, means biasing said actuator toward its initial position, a releaser normally acting to restrain said actuator against its bias and movable by 'said elect'ro-magnetic means when energized to releasing position, a second electro-magnetic means for successively advancing said actuator toward and to switch-closing position, an.energizing circuit for said second electro-magnetic means, an electro-thermal switch controlling said last-mentioned circuit, a switch in the thermal circuit of said electro-thermal switch and actuated by said second electro-magnetic means to cyclically control the electro-thermal switch, the said thermal circuit including a switch controlled by the first-mentioned electro-magnetic means, closed upon de-energization and opened upon energization of said first-mentioned electro-magnetic means.

1'1. Apparatus of the character specified in the immediately preceding claim, including switching means responsive to'variations in local conditions, and an energizing circuit for said firstmentioned electro-magnetic means controlled by said switching means.

18. A controller comprising, a switch biased to one position, electro-magnetic means for shifting said switch to its other position, an energizing circuit for said electro-magn'etic means comprising a switch, a multi-step actuator requiring a plurality of advancing steps from initial position to close said last-mentioned switch and a single-step-return movement to open said switch, means biasing said actuator toward its initial position, a releaser normally acting .to restrain said actuator against its bias and movable by said electro-magnetic means when energized to releasing position, a second electro-magnetic means for successively advancing said actuator toward and to switch-closing position, an energizing circuit for said second electro-magnetic means, an electro-thermal switch controlling said last-mentioned circuit, a switch in the thermal circuit of said electro-thermal switch and actuated by said second electro-magnetic means to cyclically control the electro-thermalswitch, the said thermal circuit including a switch controlled by the firstmentioned electro-magnetic means, closed upon de-energization and opened upon energization of said first-mentioned electro-magnetic means, switching means responsive to variations in local conditions, an energizing circuit for said firstmentioned electro-magnetic means controlled by 13 said switching means, a heating coil connected to the dead side of the first-mentioned switch and connectible with an energy source, a thermally-responsive cold-closed switch arranged within the influence of said heating coil, and an 140 energizing circuit for the first-mentioned electromagnetic means including said last-mentioned thermally-responsive switch and the secondmentioned switch, but excluding the switching means responsive to variations in local conditions. 1 5

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