US2089161A - Control system - Google Patents

Description

1937- w. H. GlLLE 2,089,161

CONTROL SYSTEM Filed June 3, 1936 1'26 w I 7442215 H. @1726 Patented Aug. 3, 1937 PATENT OFFICE CONTROL SYSTEM Willis H. Gillc, St. Paul, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application June 3, 1936, Serial No. 83,241

10 Claims. (Cl. 172-239) My invention relates to a new control system and more particularly to one of the class employing a relay switch between a main control switch and a device to be actuated.

5 An object of the present invention is to provide a control system wherein a switch operating means is initially connected in series with a motor to be operated, the circuit having suflicient impedance so that only the switch operatming means is brought into operation, and in J which upon said switch operating means being brought into operation a new circuit having a relatively low impedance is established to the motor and wherein means are provided for in- 15 terrupting said circuit after a predetermined movement of said motor. I

Afurther object of the present invention is to provide a control system of the type just'mentioned wherein the new circuit that is established to the device to be actuated shunts out the switch actuating means so as to deenergize the same and wherein means are provided for holding the switch in the position to which it has been moved by the energization of said actuating means.

25 A further object of the invention is to provide a control system employing a control switch movable between two contact making positions in control of a motor operated device which is operated between two positions and electrically operated circuit changing means wherein upon said control switch moving to either of its two contact making positions a circuit is first established to the motor operating said device through said circuit changing means and upon the re- 35 sultant operation of said circuit changing means to a circuit which is independent of said control switch.

A further object of the present invention is to provide a control system of the type set forth 40 in the previous object in which the circuit changing means consists of two electromagnetic coils and a switch movable between two contact making positions.-

Other objects of the invention will be apparent 45 from a consideration of the accompanying speci- Figure 3 is a schematic view of one form of my 5 control system, and

the reference numerals H and I2.

Figure 4 is a schematic view of a modified form of my control system.

Referring to the drawing, the relay proper which is used in the new control system on the present invention is indicated in Figures 1' and 2. This relay is of a somewhat similar structure to that shown in my co-pending application, Serial No. 758,231, filed December 19, 1934. A primary difference between therelay of my previous application and the present relay is that in the previous relay the contact arm was biased to a mid position so that when the two coils are balanced, either through both being energized or both being deenergized, thecontact arm was in mid position, whereas in the present relay the spring associated with the contact arm has an over-center snap action so that the contact. arm is in engagement with one or the other of the contacts depending upon which direction the coils have been unbalanced during the previous operation of the relay.

Referring to Figure 1 of the drawing, the tw coils of the relay are generally designated by The structure of these coils is shown in connection with a sectional". representation of coil H. In this respect, the winding of coil II is designated by the reference numeral i4. Extending through this winding is a tubular sleeve l5 of non-magnetic metal. Engaging each end of the winding H are end plates l6, which end plates are held in engagement with the winding by overturned m'ature 25 is provided at its outer ends with downwardly extending portions 28, which port-ions extend into the openings of the coil H and constitute cores therefor. Secured to the armature 25 is a downwardly extending contact arm 30, which contact arm carries adjacent its lower end oppositely disposed contacts 3| and 32. Contacts 3| and 32 are adapted to cooperate with stationary contacts 33 and 34, respectively.

It will be readily seen from the foregoing de scription and from a consideration of the drawing that in the event that coil I2 is energized and coil II is not, contact arm 30 will be moved to assume the position shown in the drawing wherein contacts ii and 33 are in engagement. If on the other hand, coil ii is energized and coil I2 is not, the core portion 28 cooperating with coil II will be drawn downwardly moving the switch arm 30 into opposite position such that contacts 32 and N are in engagement. In this respect, the structure in action 01' the relay of the present invention is identical with that'set forth in my previous application referred to above, which application may be referred to for further. details 01' construction not shown or described in the present application.

As distinguished from the relay of my previous application, the armature 25 of the present relay is provided with an upwardly extendin portion 35, which portion is provided at its upper extremity with a forwardly extending lug 3'. Over this lug is secured one end of a spring 3!, which spring extends through any suitable opening in the armature 25. The lower end of the spring 38 is secured to an inwardly extending car In which forms an integral part of casing 20. It will be noted that-the spring. is secured to the casing and to the armature upon opposite sides of the pivot pin 22 so that upon contact arm 30 being moved slightly beyond center position in either direction, the spring 38 is effective to continue to move the armature and contact arm in that direction. Moreover, upon the coils being so unbalanced that contact arm 80 is moved into engagement with either one or the other of the contacts 33 and 34, spring 38 will 'act to retain the contact arm 30 in this position. Moreover, the spring 38 will function in the usual manner 01' an over-center snap action spring to give a quick make and break action thuseliminating sparking between the contacts associated therewith.

In Figure 3, I have illustrated one form of my control system as applied to a temperature control system. The device to be controlled in this case is a fuel valve which is generally designated by the reference numeral 50. This valve may be of any conventional type, preferably of one of the types shown in the patent to George D. Bowers No. 1,861,046 issued May 31, 1932. As shown in the drawing, this figure comprises a valve casing i having the usual transverse partition 52 extending therethrough. This partition 52 is apertured in the usual manner to provide a valve opening against which is seated a valve head Ill, which in the present instance-is shown as being spherical in form, although it is to be understood that this plays no part. whatsoever in my invention. Secured to the valve head 53 is a valve stem 55 consisting of upper and lower sections of non-magnetic material between which is a member 58 of magnetic material constituting the core of a solenoid actuator for the valve. The upper section of stem 55 terminates in a reduced portion 51 on which is threaded a nut- Associated with the core- 56' are two solenoid windings 59 and 60. Upon the energizetion of winding 59, the core 56 is moved in a direction tending to center the core with respect to the winding 59 which direction is such as to move valve 53 away from its seat. desired to close the valve again, winding 50 is energized to move the core 58, and consequently the valve 53, in a reverse direction.

In order to deenergize winding '59 after the valve has been opened and in order to retain the valve in its open position after the winding 59 When it is has been deenergized, a combination cycling switch and valve retaining mechanism is provided, which mechanism is generally indicated by the reference numeral 84. This mechanism comprises a snap disc 65 which is provided with an aperture in its central portion through which the reduced portion 51 of stem 55 extends. The disc member 65 is also provide with diametrically oppositely disposed apertures 68 and i9. Cooperating with disc member 55 are contact structures ill and II. The contact structure comprises two end metallic contact members 13 and H- which are secured together through a reduced portion of insulating material, which portion extends through the aperture 68 in disc member '65. The contact structure ll comprises two end metallic members 18 and 19, which members are secured together through a center portion 80 which, in this case, is of conducting material. The portion 80 extends through aperture G9 in a manner similar to that in which portion 15 extends through aperture 68. Due to the fact that the center portion of disc 65 is deformed, disc member 55 tends to be bowed in either one direction or the other depending upon the position to which it is moved by the action of the solenoid mechanism and will be moved between these positions with a snap action. Moreover, through its cooperation with contact structures I0 and II, the disc 85 acts as a switch. It will be observed that in the position shown in the drawing in full lines, which position corresponds to the closed position of valve' 50, the disc 65 acts to connect the contact structure H, which, unlike structure Hi, is electrically continuous, with the contact member ll. In this position of the disc, it does not engage with contact member 13. When the solenoid is so energized, the stem 55 is moved upwardly snapping the disc 65 into the position shown in dotted lines in Figure 3 wherein the disc engages contact member 13 but not contact member II. The disc then acts to connect the contact structure ll with the contact member 13. Moreover, due to the snap action of the disc 65, the disc tends to remain in the dotted line position when so moved to such an extent that it will retain the valve 53 above its seat against the action of gravity. Thus. as will be readily seen, the disc 55 serves a dual function oi acting as a switch member and also acting to retain the valve in the position to which it is moved through the energization of the solenoids. The operation of this valve will be more apparent from a subsequent descripv tion of the operation of my system.

The controlling switch which may be of any desired form is shown in the drawing as corisisting of a thermostat 80. This thermostat may be of any desired form but for the purposes of illustration isshown as comprising a bimetallic element ii to which is attached a contact arm 82. This contact arm 92 carries contacts 93 and 94 which are adapted to be moved into engagement with contacts 95 and 96, respectively.

A step-down transformer is employed to sup ply power for the operation of my control system, this step-down transformer being generally indicated by the reference numeral Hi0. This transformer comprises a line voltage primary llll which is connected to suitable line wires IM. This transiormer, I00 also comprises a core I02 and a low voltage secondary llll.

The relay proper is shown somewhat schematically in this figure but inasmuch as the same reference characters are applied in a more detailed showing in Figures 1 and'2, it is deemed unnecessary to further describe this relay in the present figure. l

It will be understood that the valve 50 may be employed to control the supply" of fuel to any desired type of fuel burner, such as a gas burner. With the parts in the position shown in the drawing, the temperature of the device which is to be controlled is within the desired range of values. Under these conditions, the valve 50 is closed and no fuel is being supplied to the burner. Upon the temperature of the space being controlled falling below a desired value, the bimetallic element 9! is effective to move contact arm 92 in a direction to cause engagement of contacts 93 and 95. Upon this taking place, the following circuit is established to relay coil II: from the right-hand terminal of secondary I03 through conductors I06 and I01, bimetallic element 9!,

contact arm 92, contacts 93 and 95, conductor I09, relay coil ii, conductors H0 and III, solenoid winding 59, conductor II2, contact member I4, disc 65, contact member I9, and conductor H3 to the left-hand terminal of secondary I03. It will be noted that in the circuit just traced the coil II of the relay and the solenoid winding 59 are connected in series. Since the work performed by the coils II and I2 is relatively small compared with that performed by solenoid windings 59 and 60, the energy required by coils II and I2 for operation of the relay is relatively low as compared with that required by solenoid windings 59 and 60 for operation of the valve. Moreover, because of the low current requirement of the coils I I and I2, these coils may have a much higher impedance than the solenoid windings. In the circuit just traced, as previously stated, these two devices are connected in series so that the resistance of coil II prevents sufficient energy from being supplied to winding 59 to actuate the same. The relatively small amount of current flowing through the circuit just traced, however, is sufficient to energize. coil II with the result that contact arm 30' is moved towards the right in a direction such as to cause engagement of contacts 32 and 34.

Upon the engagement of contacts 32 and 34, the following circuit is established tosolenoid winding 59: from the right-hand terminal of secondary I03 through-conductors I06 and H5, con- .tact arm 30, contacts 32 and 34, conductors H0 and I I I, solenoid winding 59, conductor I I2, contact member I4, disc 35, contact member 19 and conductor II3 to the left-hand terminal of secondary I03. It will be noted that the new circuit does not include the winding II and, furthermore, is independent of thermostat 90.

The new circuit, because of the elimination of coil II, is of such low impedance that suflicient power is supplied to solenoid winding 59 for the actuation of valve stem 55. Furthermore, the new circuit constitutes a shunt across the coil II and as a result effectively deenergizes the same. In addition, the new circuit is independent of the thermostat so that the thermostat- 90 is not only freed from excessive current load on its contacts such as is necessary for the operation of device 59, but, moreover, the operation of the valve to open position is independent of the thermostat so that it is impossible for the system of the present invention, the only time that the main motor winding 59 is connected in series with the thermostatic contacts, the relatively high resistance relay winding II is also in the circuit so that current flowing through the same has such a small value that the thermostatic contacts are entirely capable of carrying the same.

Upon the solenoid winding 59 being energized in the manner previously explained, core 56 is moved upwardly, also in a manner previously explained. The result is that disc 65 is snapped over-center, which action serves to move the left-hand portion of disc 65 away from contact member I4 and into engagement with contact member I3, thus breaking the previously traced circuit to solenoid winding 59. At the same time, the upward snapping of disc 65 serves to hold the valve 53 away from its seat upon deenergization of winding 59. This action is more fully set forth in the Bower patent previously referred to and for a more full understanding of the action of the same, reference is made to that patent.

Upon the valve 50 being moved away from its seat in the manner described; fuel is supplied to the burner, or other heat producing device. Sooner or later, the temperature of the space to be controlled is raised sufliciently to cause bimetallic element ill to be heated to the point where contact arm 92 is moved to the right sufficiently to cause engagement of contacts 94 and 96. Upon this taking place, the following circuit is established to relay coil I2: from the righthand terminal of secondary I 03 through conductors I06 and I01, bimetallicelement 9i, contact arm 92, contacts 94 and 96, conductor H8, relay coil I2", conductors. H9 and I20, solenoid winding 60, conductor I2I, contact member I3, disc member 65, contact member 18, contact member 19 and conductor II3 to the left-hand portion of secondary I03. It will be noted that in the circuit just traced, the relay coil I2 and in a manner similar to the way in which relay coil I I and solenoid winding 59 were connected in the first circuit which was'traced in the description of the operation of this system. As in the previous case, the presence of the resistance of relay coil I2 in the circuit prevents sufficient current from being supplied to winding 60 to cause actuation of valve stem 55 against the biasing action of spring 65. Also as in the previous case, thecurrent flowing through the circuit is slimcient to energize coil I2 to the point where it is effective to move contact arm 30 to the left against the action of biasing spring 38 so as to cause engagement of contacts 3| and 33.

The-engagement of contacts 3I and 33 causes the following circuit to be established to solenoid winding 60; from the right-hand terminal of secondary 103 through conductors I06 and 5, contact arm 30, contacts 3| and 33, conductors I22 and I20, solenoid winding 60, conductor I2I, contact member 13, disc member 55, contact structure 'II, and conductor II3 to the lefthand terminal of secondary I03. It will be noted 'that the last traced circuit d es not include the relay coil I2'and is independent of the thermostat 30. In this respect, the action is identically the same as that described in connection with the energization of solenoid winding 59.

The energization of solenoid winding causes core 56 to be moved downwardly against the biasing action of disc causing disc 65 to be snapped over-center with the result that valve 53 is moved to the closed position shown in the drawing, in which position it is held by the action of disc 65. At the same time, the previously traced circuit through winding 60 is interrupted through the left-hand portion of disc 65 moving away from contact member 13 and into engagement with contact member 14. The engagement of disc 65 with contact member 14 does not, however, cause the establishment of any circuit inasmuch as contact 93 is not in engagement with contact 95 nor is contact 32 in engagement with contact 34. The system is, accordingly, not again placed in operation until the temperature again falls to the point where contacts 93 and 96 will move into operation whereupon the previously described cycle of operation is repeated.

It will be readily seen from the foregoing description, that by the use of my improved control system it is possible to operate a device having a rather large current demand with a control switch which has a relatively low current carrying capacity and whose contact making positions are unstable. It will furthermore be seen that this is accomplished through an extremely simple and relatively inexpensive apparatus. Moreover, as previously indicated, while I have described my control system in Figure 3 as applied to temperature control, it is obvious that it may be applied to any type of a control system for an electrically actuated device. Furthermore, the system is of broader applicationthan where the control switch is of any particular type. Moreover, while I have shown the device to be operated as of being of a well known type, which in effect employs two motors, one for operating the device in one direction and the other for operating the device in the other direction, it will be understood that the system may well be applied to any other motor operated device, which is successively actuated between two positions. Thus in Figure 4, the control system which forms the inventive subject matter of the present application is applied to the control of a somewhat different type of motor operated device.

Referring to said figure, a portion of a furnace is designated by the reference numeral I25. This furnace may be of any desired construction and may be provided with as many diiferent draft controls as is customary in the art. However, since the particular construction of the furnace and the particular draft control arrangement forms no part of the present invention, only the draft damper I26 is disclosed. This draft damper is pivotally mounted in the usual manner and biased to a closed position.

Connected to the damper I26 is a chain. I28, or other suitable flexible connecting member which is connected at its'opposite end to a crank arm.

I29 of a shaft I30. This shaft constitutes a main shaft of a damper motor unit generally desiggearing I36.

Secured to the shaft I30 is a cam I36 which is designed to actuate a switch blade I31. The switch blade I31 is provided with a cam follower portion I30 and cooperates with two contacts I39 and I40. The cam I36 is provided over 180 degrees of its circumference with a raised toe portion I42. The relation of the various parts is such that when the cam follower I38 is in engagement with the raised portion of the cam I36, switch blade I31 is in engagement with contact I39. 0n the other hand, when the cam follower I38 is in engagement with the depressed portion of the cam surface of cam I36, the switch blade I31 is in engagement with contact I40. Thus it will be seen that switch blade I31 is in engagement with contact I39 for 180 degrees of rotation of shaft I30 and in engagement with contact I60 for the other 180 degrees of rotation of shaft I30. The position of the cam with respect to crank arm I29 is such that switch arm I31,is moved from one contact to another when crank arm I 29 reaches its uppermost and lowermost position, respectively. These positions of crank arm I 29, as will be obvious from the drawing, correspond to the closed and open positions of damper I26. The switch blade I31 and its associated contacts accordingly function as a cycling switch to-terminate the operation of the motor at the end of each cycle.

A step-down transformer is employed to supply power for the operation of the system. This transformer comprises a line voltage primary I50 which is connected .to line wires I5I. The transformer also comprises a core I52 and a low voltage secondary I53.

Inasmuch as the thermostat may be the same in construction as that of Figure 3 and since its operation is in no respect different from that of Figure 3, the same reference characters have been applied to this thermostat as to the corresponding thermostat in Figure 3. Moreover, the same reference characters are also applied to the relay as are applied to this device in the previous figures.

With the parts in the position shown in Figure 4, the temperature of a space in which thermo stat is located is within the range of the temperature desired to be maintained. The draft damper I26 is, accordingly, closed so that the furnace I25 is supplying a minimum amount of heat. The arrangement of bimetallic element 9| with respect to contact arm 92 is such that upon a decrease in temperature the arm 92 is deflected to the left. If such a decrease does occur in the room, as is likely in view of the closed position of damper I26, contact arm 32 will be moved suiiiciently to the left to cause engagement of contacts 33 and 95. When this occurs, the following circuit will be established to relay coil II: from the right-hand terminal of secondary I53, through conductors I60 and "SI, bimetallic element 9|, contact arm 32, contacts 93 and 95, conductor I62, relay coil I'I, conductors I63 and I64, contact I39, switch arm I31, conductor I65, motor field winding I33 and conductor I66 to the lefthand terminal of secondary I53.

It will be noted that in the circuit previously traced the relay coil II and the motor winding I33 are connected in series. Due to the fact that the relay coil I I requires a relatively low current consumption for operation thereof, sufficient power will be supplied to the relay coil II for operation thereof but insufficient power will be supplied to the motor winding to cause operation of the motor. This action is exactly similar in this respect to that shown in Figure 3 and the advantages of this feature are substantially the same as set forth in connection with Figure 3.

The energization of relay coil II causes the left-hand core 28 to be drawn downwardly rotating the armature in a counter-clockwise direction and causing contacts 32 and 34 to be moved into engagement. As soon as this is done, the following circuit is established to the motor field winding I33: from the right-hand terminal of secondary I53, through conductors I60 and I68,-

' contact arm 30, contacts 32 and 34, conductors I69 and I64, contact I39, switch arm I31, conductor I65, field winding I33 and conductor I66 to the left-hand terminal of secondary I53. It will be noted that in this new circuitboth the thermostat 90 and the relay coil II are shunted out. This will result in insuring that the motor will continue to operate even though there is a momentary separation of thermostat contacts 93 and 95. Moreover, the-circuit just traced is of suilicient low impedance that the motor will be supplied with sufilcient energy to operate in a normal manner. The result will be that the shaft I30 will be rotated in a. direction indicated by the arrow adjacent cam I36 causing crank arm I29 to move damper I26 to an open position. This rotation will continue until crank arm I23 reaches a, substantially vertical position, at which time the cam follower I38 will ride oil of the raised portion of cam I36 causing the switch arm I31 to separate from the contact I39 and move into engagement with contact I40. When thisoccurs, the previously traced motor. circuit will be interrupted through the separation of switch blade I3! from contact I39 so that the operation of the motor is terminated leaving crank arm i 39 in a vertical position.

'As a result or the previous operation, the damper is placed in its full open position with the result that the furnace is delivering heat at a much more rapid rate than previously. The result of this is that the temperature in the space heated by the ice, in which the thermostat is located, will normally soon rise to such a value as to cause switch arm 90 to be deflected sumciently to the right to cause engagement of contacts Qt and 9%. When this occurs, the following circuit will be established to relay coil H: from the right-hand terminal of secondary 833, through conductors itll and N56, bimetallic elemerit ill, contact arm 9?,- contacts 9t and 38,

till! conductor (I'll, relay coil it, conductor Hi2, contact Mt, switch arm 03?], conductor Nit, motor field winding and conductor W5 back to the left-hand terminal oi secondary E53. It will be noted that in the circuit just traced the relay coil i2 is connected in series with the field wind= ing i233. This operates in a manner similar to that set forth in the previous cases to restrict the flow of current through the circuit to a value which is just sumcient to operate the relay but is insumcient to either harm the thermostat contacts or cause operation of the motor.

The energization of relay coil i2 causes the armature to be rotated in a clockwise direction so that the parts assume the position shown in Figure 4 wherein contacts 3i and 33 are in engagement. This causes the following circuit to be established: from the right-hand terminal of secondary I53, through conductors I60 and I68, contact arm30, contacts 3| and 33, conductor I'll contact M0, switch arm I31, conductor liid, field winding i333, and conductor 56 to'the lefthand terminal of secondary I53. With the establishment of the new circuit, the relay coil I2 and the thermostat are shunted out in a man-- 'ner similar to that in connection with the previously described operation of the system so that the motor I33 is supplied with sufficient power for operation. The result is that shaft I30 is again rotated in the direction of the arrow adjacent cam 36 causing the crank arm to be lowered and closing damper I26. This rotation continues until crank arm I29 is in substantially its lowermost position at which time cam follower I38 will ride up on the left portion 2 of cam I36 causing a separation of switch blade I31 from contact 140 and engagement of the switch blade with contact I39. This will terminate operation of the motor until the thermostat 90 again calls for hea or in other words, until contacts 93 and are again moved into engagement. 'I'he'parts' will then be in the position shown in the drawing and upon such engagement of the thermostatic contacts, the described cycle of operation will be repeated.

From the described operation of Figures 3 and 4, it will be obvious that my control system is readily applicable to a variety of electrically operated devices. It will furthermore be seen that the device of the control system wherein it is possible to control a device using a rather large amount of current for operation with a switch which is either unstable in its contact making position or is unadapted to carry large currents; or both. It will furthermore be seen that I have devised a simple and compact relay structure for use with my control circuit.

While I have shown certain specific embodiments of my invention, it is to be understood that these are for purposes of illustration only and' that my invention is to be limited only by the scope of the accompanying claims.

I claim as my invention: i i 1. In a control system, an electrically operated motor, a switch, electromagnetic operating means for said switch requiring a lesser amount of energy for operation than said motor, a source of energy, means for-establishing a circuit connecting said motor and. said electromagnetic operating means with said source of energy, said circuit having a sciently high impedance that only said electromagnetic operating means is brought into operation to move said switch into a circuit making position, means effective upon said-switch being moved into said circuit making position to establish a circuit to said motor or sufficiently low impedance to cause operation of said motor, and means operative to interrupt said last named circuit after a predetermined movement of said motor.

2. In a control system, an electrically operated motor, a switch, electromagnetic operating means for said switch requiring a lesser amount of energy for operation than said motor, a source of energy, means for establishing a circuit connecting said motor and said electromagnetic operating means with said source of energy, said circuit having a sumciently high impedance that only said electromagnetic operating means is brought into operation to move said switch into a circuit making position, means to retain said switch in said circuit nraking position independently of said operating means, means effective upon said switch being moved into said circuit making position to establish a circuit to said motor of surficiently low impedance to cause operation of said motor and to deenergize substantially saidoperating means, and means operative tointerrupt said last named circuit after a predetermined movement of said motor.

- 3. In a control'system, electrically operated motor means requiring a relatively large amount of energy for operation, a control switch movable between first and second contact making positions, a second switch, first and second electro magnetic operating means therefor, said first operating means being effective when energized to move said second switch into a first contact making position and said second operating means being effective when energized to move said second switch into a second contact making position, both of said operating means requiring a relatively small amount of energy for operation, a source of energy, means operative upon said control switch being moved into said first contact making position to establish a circuit connecting said motor means and said first electromagnetic -operating means with said source of energy, said circuit having a sufiiciently high impedance that only said first electromagnetic op-" erating means is brought into operation to move said second switch into said contact making posi- "tion, yieldable means to retain said second switch in said position when so moved, means eii'ective upon said second switch being so moved to establish a circuit to said motor means independently of said control switch and of sufliciently low impedance to cause movement of said motor means,

switching means eflective to interrupt said circuit upon a predetermined movement of said motor means, means eflfective upon said control switch being moved to said second circuit making position to establish a circuit between said source of energy and said second electromagnetic operating means to move said second switch intosaid second contact making position andcircuit means eflective upon such movement of the second switch to cause said motor means to be reenergized.

4. In a condition control system, a condition responsive switch movable between two contact making positions corresponding to low and high values of said condition, condition changing means, an electrically operated controlling means therefor'adapted to be moved between a position in which said condition changing means is eiIec-. tive to change the value of the condition in one direction and a position wherein the value of the condition tends to vary in the other direction, a circuit changing means requiring a relatively small amount of energy 'for operation thereof, means effective upon said condition responsive switch being moved to either contact making position to cause a circuit to be established from said source of energy to said controlling means through said circuit changing means, said circuit having a suiiiciently high impedance that only said circuit changing means is brought into operation, and means effective upon'such operation of said circuit changing means to establish a circuit to said controlling means independently of said condition responsive switch and of sufllciently low impedance as to cause operation of said controlling device from one to the other of its two positions.

5. In a control system, a control switch movable between two contact making positions, a device to be operated between two positions, electrical motor means for operating said device, electrically operated circuit changing means requiring a lesser amount of energy for operation than said motor means, a source of electrical through said circuit changing means, said circuit having a sufliiciently high impedance'that only said circuit changing means is brought into operation, and means eii'ective upon such operation of said circuit changing means to establish a circuit to said motor means independently of said control switch and oi sufiiciently low impedance as to cause operation of said motor means from one to the other or its two positions.

6. In a control system, a control switch ,movable between two contact making positions, a device to be operated between two positions, electrical motor means for operating said device, electrically operated circuit changing means requiring a lesser amount 01' energy for operation than said motor means, a source of electrical ener y. and means eiiective upon said control switch being moved to either contact making position to cause a circuit to be established from said source of energy to said motor means through said circuit changing means, said circuit having a sumciently high impedance that only said circuit changing means is brought into operation, means effective upon such operation oi said circuit changing means to establish a circuit to said motor means independently of said control switch ,vice in one direction upon said control switch being moved into one contact making position and in the opposite direction upon said control switch being moved into its other contact making position.

'1. In a control system, a control switch movable between two contact making positions, a device to 'be operated successively between two positions, a pair of electric motor means, one to cause operation 01' said device in each direction, a relay comprising a pair of relay coils and i a switch movable between two contact making positions by the respective energization of said coils, a source of electrical energy and circuit means operable upon said control switch being moved to either contact making position to establish an energizing circuit to one oi? said relay coils through one 01' said motor means to cause said relay switch to be moved from one to the other of its contact making positions, said circuit means being effective upon said relay switch being so moved to establish an energizing circuit to said one motor means independently of said one relay coil.

8. In a control system, a control switch movable between two contact making positions, a device to be operated successively between two positions, a pair oi. electric motor means, one to cause operation of said device in each direction, a relay comprising a pair of relay coils and a switch movable between two contact making positions by the respective energization of said coils, a source of electrical energy and circuit means operable upon said control switch being moved to either contact making position to establish an energizing circuit to one of said relay coils through one oi! said motor means to cause said relay switch to be moved from one to the other 0; i s contact making positions, said circuit means 3 and a switch movable between two contact mak ing positions by the respective energization of said coils, a source of electrical energy, circuit means operable upon said control switch being moved to either contact making position to establish an energizing circuit to one of said relay coils through one of said motor means to cause said relay switch to be moved .from one to the other of its contact making positions, said circuit means being effective upon said relay switch being so moved to establish an energizing circuit to said one motor means independently of said one relay coil, and switching means effective to interrupt both of said circuits upon said device reaching the extreme position to which it is moved as the result of the energization of said motor means.

10. In a condition control system, condition changing means, control means, control means movable from a position in which the value of the condition is increased to a position wherein the value of the condition is decreased, motor means for moving said control means between said twopositions, a condition responsive switch movable between two contact making positions, a relay comprising a pair of relay coils and a switch movable between two contact making positions upon the respective energization of said coils, a source of electrical energy, circuit means ef fective upon the condition responsive switch moving to one of said two contact making posi tions to establish an energizing circuit to one of said relay coils through said motor means tocause said relay switch to be moved from one to the other of its contact making positions, said circuit means being effective upon said relay switch being so moved to establish a circuit to said motor means independently of said relay coil, and switching means operated by said motor to terminate operation of said motor upon said control means reaching one of said positions until said condition has changed sufiiciently to cause said condition responsive switch to assume the other of its contact making positions.

WILLIS H. cm.

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