US2028110A

US2028110A - Remote control system

Info

Publication number: US2028110A
Application number: US15264A
Authority: US
Inventors: Daniel G Taylor
Original assignee: Honeywell Inc
Current assignee: Honeywell Inc
Priority date: 1935-04-08
Filing date: 1935-04-08
Publication date: 1936-01-14
Anticipated expiration: 1953-01-14

Description

Jan; 14, 1936. D. G. TAYLOR REMOTE CONTROL SYSTEM Filed April 8, 1935 Dainiel G. Taylor W MM Patented Jan. 14, 1936 UNITED STATE PATENT OFFICE 2,@28,l.1ii

REMOTE OQiNTROL SYSTEM Application April 3, 1935, Serial No. 15,264

16 Claims.

The present invention relates to electrical systems of control by which a device or mechanism to be controlled may be modulated or propertioned. In systems of this type, it is now common practice to provide one or more variable resistance controllers which control the respec tive energization of a pair of electrical oppositely acting devices that operate a switching mechanism which in turn, either directly or through the medium of a relay, control motor means that positions the device to be controlled or operated, this same switching mechanism also being controlled by the motor means either mechanically, or electrically by having the motor means control a further variable resistance that is associated with the oppositely acting devices so as to rebelance the energizations of the same when the de vice to be controlled or operated has been properly positioned.

In such arrangements, the switching mechanism that operates the motor means, either directly or indirectly, and the oppositely acting electrical means for controlling the same, are operated to various circuit controlling positions by reasons of relatively small changes in the associated controlling variable resistances and might be termed a marginal device or mechanism in that the switch arm of the switching mechanism is very gradually and slowly moved towards and away from the associated contact or contacts so that the contact pressure at the moment of the original engagement or disengagement of the switch arm and associated contact or contacts is very light, thereby making such switching mech- 5 anism extremely sensitive to vibrations and the like. In order to overcome this difliculty in commercial apparatus of this nature, it has been usual to provide some means for increasing the contact pressure between the switch arm of the switching mechanism and the associated contact or contacts whenever a circuit is completed therethrough.

In the'past, one form of contact pressure increasing arrangement has included small auxil- 5 iary electrical devices which cooperate with the oppositely acting electrical devices and are energized upon engagement of the switch arm of the switching mechanism with its associated contact or contacts and are deenergized upon disengagement of such parts. Another form has taken the form of connections between such switching mechanism and a portion of the oppositely acting electrical devices whereby such portions are additionally energized upon engagement of the switch 5 arm of'the switching mechanism and its contact or contacts. While these arrangements are entirely satisfactory from an operating standpoint, they are relatively expensive from a production standpoint. The present invention relates to an improved and simplified arrangement for 'obtain- 5 ing increased contact pressure in arrangements of the type discussed above.

An object of the present invention, therefore, is the provision of a simplified and improved contact pressure increasing arrangement for use in m electrical systems of the proportioning or modulating type, the new and improved arrangement being such as to readily adapt itself to high quantity production.

A further object or the invention is the pro- 35 vision of an electrical "proper-timing or modulating system employing a switching mechanism operated by normally balanced oppositely acting electrical devices in which resistance means are associated with the switching mechanism in such 0 manner that engagement of the switch arm thereof with an associated contact as the result of unbalance of the normally balanced oppositely acting electrical means causes a further unbalance thereof in the same direction without the use of auxiliary electrical devices and without the necessity of connecting such resistance means intermediate the ends of the windings of the normally balanced oppositely acting electrical devices.

Further objects of the invention willbe found 30 in the drawing, the description and the accompanying claims.

For a more complete understanding of the invention, reference may be had to the following detailed description and the accompanying draw- 35 ings in which:

Fig. 1 shows the invention applied to an electrical proportioning or modulating system of the electrically balanced type, and

Fig. 2 shows the invention applied to an electrical modulating or proportioning system of the mechanically balanced type.

The systems of the present invention have particular utility in the field of air conditioning for controlling dampers, valves and the like and such an application of the systems of the present invention has been shown in Fig. 1 of the drawing. Referring to Fig. l, a device for controlling a condition has therein been shown in the form of a valve indicatedat ID, The valve I0 may be utilized to control the flow of fuel to a burner, the flow of a heating or cooling medium to suitable heat transferring apparatus, or in any other desired manner.

The valve I0 is shown as provided with a suite- I 23 cooperate with the respective rotors l5 and Energization of the field windings l9 and 25 is herein shown as controlled by a relay which is illustrated as beirig of the electromagnetic type although it will be readily understood that any other suitable type of relay could be utilized. This relay includes a pair of relay windings 22 and 23 which control a single plunger 25. The windings 22 and 23 may be entirely separate or may be obtained by providing a single winding with a center tap. The plunger 25 is connected to a relay switch arm 25 through a suitable connecting means 25. The switch arm 25 cooperates with a pair of spaced stationary contacts 23 and 28. Contact 21 is connected to one end of field winding l9 by means of a wire 25 and contact 28 is similarly connected to one end of field winding 20 by a wire 35. Theother ends of the field windings l9 and 25 are both connected to a line wire 3i by means of a wire 32 and the switch arm 25 is connected to a line wire 33 by a wire 33. It will be readily apparent that upon engagement of switch arm 25 with contact 21, the field winding 89 is energized and that, upon engagement of switch arm 25 with contact 28, the field winding 20 is energized.

The relay windings 22 and 23 are controlled by a switching mechanism comprising a switch arm 35 that is pivoted at 35 and which cooperates with

spaced contacts

31 and 38. The switch arm 35 is connected to a plunger 39 by suitable connecting means 30 and this plunger 39 is controlled by a pair of normally balanced oppositely acting electrical devices, herein shown in the form of a pair of electromagnetic windings 3i and 32. The windings tit and 52, as in the case of windings 22 and 23, may be entirely separate or may take the form of a single winding that is provided with a center tap. It is to be understood that the switch arm 35 could be controlled by oppositely acting electrical devices other than of the electromagnetic types.

The energizations of the windings 4H and G2 are controlled, in part, by a variable resistance type of controller herein shown as a potentiometer thermostat. This potentiometer thermostat includes an actuating element 415, herein shown as comprised of bimetal and having one of its ends secured as at 65. The other end of bimetallic element 35 operates a control contact arm M which, upon temperature changes, sweeps back and forth across a control resistance 68. In the electrically balanced type of system shown in Fig. 1, the energization of windings ill and 52 are also controlled, in part, by a variable balancing resistance means, herein shown as comprising a potentiometer which includes a balancing resistance as that is adapted to be traversed by a balancing contact arm 55 which is secured to the main operating shaft i l.

The line wires 3i and 33 supply power to a stepdown transformer 52, having a high voltage primary 53 and a low voltage secondary 56. The

windings Ali and .32, in series, are connected across the secondary 5d of transformer 52 by means of

wires

55, 55, 53 and 58. Similarly, the relay windings 22 and'23, in series, are connected across the secondary of transformer 52 by

wires

55, 59, 55, 5

l

62 and 58. The control resistance 33 and the balancing resistance 43, in parallel, are connected in and the switch arm 35 is connected to the junction of wires l5 and 12 through a resistance means 75 by means of wires ll and 18. The contact 3'? is connected to the junction of wires 5! and 52 by a wire 19 and the junction of

wires

53 and 55 is similarly connected to contact 38 by a wire 30.

Operation of the system of Fig. 1

The bimetallic element 35 of the potentiometer thermostat may respond to any desired temperature condition, such, for instance, as the temperature of a space to be controlled and, with the parts in position shown, this temperature is intermediate the permissible -or desired high and low limits. As a result, control contact arm t! is engaging the central portion of control resistance 38. Similarly, the balancing contact finger 55 is engaging the central portion of balancing resistance 59, The two windings 3i and 52 are therefore equally energized and the plunger 35 is in a central position so that switch arm 35 is

intermediate contacts

31 and 38 and is not engaging either one of them. As a result, relay windings 22 and 23 are equally energized and the plunger 23 is in a central position whereby switch arm 25 is intermediate contacts 21 and 28. Field windings I 9 and 20 are therefore both deenergized and the main operating shaft it is stationary. With the parts in this position, the valve in is open to a predetermined extent; for instance, half open, so as to permit a predetermined heating or cooling of the space to be controlled.

Now if the temperature to which bimetallic element 45 responds should fall, control contact arm ll will move along control resistance 58 towards the right hand end thereof. Such movement of control contact arm 37 rearranges the resistance connected in circuit with the windings M and 52 in such manner that the winding 5!. becomes more highly energized than Winding 32. Plunger- 39 therefore moves to the left and when this unbalance in the energizations of windings ll and 52 has become suficient, switch arm 35 will lightly engage contact 38. When this occurs, relay Winding 22 is substantially short-circuited, complete short-circuiting being prevented by the protective resistance l5. By proper design of the relay windings 22 and 23, this protective resistance l5 could be omitted but it has been found more commercially practicable to make the relay windings 22 and 23 of relatively low impedance so that the use of a protective resistance is desirable. It will be noted that current can now fiow from the secondary 55 of transformer 52 by way of

wires

58, 52, and 5| through relay winding 23 at which point the circuit branches and a part thereof goes by way of relay winding 22, wire 65, wire 59, wire 55 to the other side of secondary 5 5 whereas the other part goes through 75 with contact 38.

protective resistance 15, switch arm 35, contact 38, wire 80, wire 59 and wire 55 to the same side of secondary 54. Relay coil 23 is therefore more highly energized than relay coil 22, whereupon plunger 24 is forcibly moved in a right hand direction sufliciently far to bring switch arm 25 into solid and firm engagement with contact 28. Field winding 20 is thereupon energized by the following circuit: line wire 33, wire 34, relay switch arm 25, contact 28, wire 30, field winding 20 and wire 32 to line wire 3|.

It will be noted that engagement of switch arm 35 with contact 38 also caused resistance 16 to be connected in parallel with the winding 42. The left hand end of winding 42 and the upper end of resistance 16 are permanently interconnected by

wires

14 and 12 and 18, whereas the right hand end of winding 42 and the lower end of resistance 16 are now interconnected by

wires

56, 59 and 88, contact 38, switch arm 35 and wire 11. This placing of resistance 16 in parallel with the winding 42 causes a further reduction in the current flowing therethrough, whereupon plunger 39 pulls switch arm 35 firmly into engagement In this manner, the contact pressure between switch arm 35 and the contact 38 is increased so that a good firm contact is made and all possibility of chatter is eliminated.

Energization of the field winding 28 causes rotation of motor rotor I1 in such a direction as to rotate main operating shaft M in a clock-wise direction when viewed from the left. Balancing contact arm 58 therefore moves upwardly along balancing resistance 49 and gradually rebalances the energization of windings 4| and 42. When the energizations of windings 4| and 42 have been sufficiently rebalanced, plunger 39 will have moved to the right sufiicintly to separate switch arm 35 from contact 38. When this occurs, relay windings 22 and 23 are again connected across the secondary 54 of transformer 52 in series so that they are equally energized. Plunger 24 then returns to the position shown whereupon field winding 28 is deenergized. Separation of switch arm 35 from contact 38 also disconnects the right hand end of winding 42 from the lower end of resistance 16 whereby the current flow through winding 42 is increased so that the plunger 39 moves further towards the right and increases the space between switch arm 35 and contact 38.

This clockwise movement of main operating shaft l4 caused an upward movement of rack l2 whereupon valve III was opened more widely. Valve [0 is now in a more .widely open position so. that more heat is supplied to the space to be controlled whereby to counter-act the fall in temperature which caused control contact arm 41 to move along control resistance 48 towards the right hand end thereof.

If the temperature of the space being controlled should fall to the permissible minimum, control contact arm 41 will move to the extreme right hand end of control resistance 48 whereupon winding 42 will be substantially completely short-circuited, complete short-circuiting being prevented by reason of the protective resistance 54. Under these conditions, it will be noted that the protective resistance 64 and the winding 42 are connected directly in parallel, the junction of winding 4| and 42 being connected to the upper end of protective resistance 64 by means of wire 14, wire 13, bimetallic element 45, control contact arm 41 and wire 68, whereas the right hand end of winding 42 is connected to the lower end of protective resistance 84 by wire 10. Plunger 39 will again move to the left so as to bring switch arm 35 into engagement with contact 38 whereupon field winding 20 will be energized again. Resistance 15 will again be placed in parallel with winding 42 whereupon the current fiow therethrough is further reduced so that the con-= tact pressure between switch arm 35 and contact 38 is again increased as explained above. The main operating shaft M will now be rotated in a clockwise direction until balancing contact finger 58 engages the extreme upper end of balancing resistance 49 whereupon winding 4| will be substantially short-circuited, complete short circuiting being prevented by protective resistance 63 which is placed in parallel therewith as will be evident upon an inspection of the wiring diagram. The system will then again be rebalanced and the field winding 28 will be dcenergized. At this time, the valve M has been moved to full open position. It will be readily apparent, that a suitable limit switch may be utilized if desired to limit the extreme movement of main operating shaft M in clockwise direction and that a similar limit switch may be utilized to limit the extreme counter-clockwise movement of main operating shaft 54 in the opposite direction.

Whenever the temperature to which bimetallic element 45 responds rises, control contact arm 41! will move along control resistance 48 towards the left hand end thereof whereupon winding 42 will become more highly energized than winding 4|. Plunger 39 thereupon will move toward the right and switch arm 35 is slowly and gradually moved toward contact 371 until the two engage.

When this occurs, protective resistance 75 will be placed in parallel with relay winding 23 so that relay 22 becomes more highly energized and plunger 24 moves quickly to the left thereby bringing relay switch arm 25 into f lm engagement with contact 21. Field winding i 9 is thereupon energized by a circuit as follows: line wire 33, wire 34, relay switch arm 25, contact 21, wire 29, field winding l9 and wire 32 to line wire 3|. Rotor I6 therefore rotates in a direction such as to cause rotation of main operating shaft M in a counter-clockwise direction as viewed from the left.

Engagement of switch arm 35 with contact 31 also places resistance 16 in parallel with winding 4|. The right hand end of winding 4| or the junction of windings 4| and 42 is connected to the upper end of resistance 15 by wire 14, wire 12 and wire 18 as before explained. The left hand end of winding 4| is now connected to the lower end of resistance 16 by wire 51, wire 62, wire 19, contact 31, switch arm 35 and wire 11. The flow of current through winding 4| is thereby further reduced so that plunger 39 forces switch arm 35 into firm contact with contact 31.

This counter-clockwise movement of main operating shaft M will continue until balancing contact arm 58 has been moved downwardly along balancing resistance 49 sufficiently to substantially rebalance the energizations of windings 4| and 42 so that plunger 39 moves towards the left far enough to just separate switch arm 35 from contact 31. When this occurs, the energizations of relay windings 22 and 23 will again be rebalanced so that relay switch arm 25 disengages contact 21 and field winding I9 is deenergized. Separation of switch arm 35 from contact 31 also disconnects the lower end of resistance 16 from the left hand end of winding 4| so that the resistance 16 and winding 4| are no longer connected in parallel whereupon the enwinding with center tap.

ergization of winding til will increase somewhat. As a result, switch arm 35 moves further away from contact 31 so that the same are sufiiciently widely spaced apart to prevent an immediate reengagement without any further temperature change. This counter-clockwise change movement of main operating shaft it caused a downward movement of rack I2 so that valve Ill was partially closed.

In this manner, by the simple inclusion of a single resistance 73 through novel and extremely simple circuit connections, an increased contact pressure is provided between switch arm 35 and its cooperating

contacts

31 and 33 without resorting to'the use of auxiliary winding and without running connections intermediate the ends of windings Q! and 32. The apparatus can therefore be built more readily and with a smaller expenditure of time and therefore at a lesser cost.

Turning now to Fig. 2 of the drawing, a modified arrangement is disclosed wherein the invention is applied to an electrical proportionating or modulating system of the mechanical followup type, the intermediate relay also being omitted. Inthis modification, there is a main operating shaft which may be utilized to drive any suitable device such as the valve IQ of Fig. 1. This main operating shaft 85 is connected to a rotor shaft 85 through suitable reduction gearing generally indicated at 81. Two

rotors

88 and 89 are carried by and secured to rotor shaft 86 and are respectively provided with cooperating field windings and M. These motors, comprised by the

rotors

88 and 89 and the associated field windings 90 and iii, are of equal power and are arranged to rotate in opposite directions upon energization. The field windings 9D and SI are normally constantly energized by being connected in series across the secondary 92 of a step-down transformer 93 having a high voltage primary 96 that is connected to

suitable line wires

95 and 96. The series circuit by which the field windings 90 and 9| are normally connected in series across the secondary 92 is as follows: secondary 92, wire 91, wire 98, wire 99, field winding 90, field winding Si, wire I06, wire IOI and wire I02 to the other side of secondary 92.

The field windings 90 and SI normally both being energized to the same extent, their associated

rotors

88 and 89 exert equal and oppositely acting torques upon the rotor shaft 86 whereby the main operating shaft 85 normally remains stationary. These field windings 90 and EI are adapted to be selectively short-circuited whereby one or the other of them is operatively deenergized so that the other is rendered capable of rotating the main operating shaft 85. This selective short-circuiting is accomplished by suitable switching mechanism that includes a suitable segmental plate I05 which is pivoted at I03 and is provided with suitable teeth Iil'l which cooperate with a worm I68 that is mounted upon and secured to the main operating shaft 85. Mounted upon plate I05 at a point indicated at I09 is a flexible switch arm H0 which is adapted to cooperate with a pair of spaced contacts III and I I2 that are carried by the plate I65.

The switch arm H0 is controlled by a pair of oppositely acting electrical devices herein shown as comprising-a pair of windings H3 and H4 which may either take the form of separate windings or may be obtained by providing a single These two windings aoeaiio I I3 and I I6 control the position of a; single plunger H5 which is connected to the switch arm Ill! 7 through suitable connecting means indicated at Mt. These windings H3 and H3 are connected across the secondary 92 of transformer 93, in series, by wire QI, wire I III, wire I I 3 and wire I32.

The respective energization of windings H3 and lid may be controlled by any suitable controlling device which is herein shown in the form of a potentiometer thermostat. This potentiometer thermostat includes a temperature responsive element II9 shown in the form of a curved bimetallic strip which has one of its ends secured .as indicated at I20. The other end of bimetallic strip II9 carries a controlling contact arm I M which is adapted to sweep back and forth across an associated control resistance I 22 upon changes in temperature. The control resistance I22 is connected in parallel with the series connected windings M3 and H6, and preferably through protective resistances I23 and I23, by means of wires I25, I26, I 2I and I28. The bimetallic strip H9, and therefore the control contact arm IN, is connected to the junction of windings of M3 and H4 by means of wires I29 and I30.

Switch arm III! is connected to the junction of field windings 90 and 9| by means of wires I3I and I32. The other end of field winding 90 is connected to contact III by means of wires 89 and I33whereas the other end of field winding 9| is connected tocontact H2 by means of wires I00 and I36.

In order to provide for increased contact pressure between switch arm H0 and its associated contacts I II and I I2, in a manner that will hereinafter be set out in detail, a resistance I35 is connected to the junction of wires I3I and I32 by means of a wire I36 and is connected to the junction of windings II 3 and II 3 by being connected to the junction of wires I 23 and I30 by means of a wire I31.

Operation of the system of Fig. 2

With the parts in the position shown, the temperature to which bimetallic strip II9 responds is intermediate or normal so that the controlling contact finger I2I engages the center of control resistance I22. Windings H3 and H3 are therefore equally energized and the switch arm IID is in a vertical position. The plate I05 is in such position that contacts I II and H2 are both out of engagement with the switch arm III). As a result, field windings 90 and iii are connected in series across the secondary 92 of transformer 93 whereby they are equally energized and the main operating shaft 85 is stationary. With the parts in this position, assuming that the main operating shaft 85 controls the valve IQ of Fig. 1, the valve would be in half open position. If the temperature to which bimetallic element I I9 responds should now rise, control contact finger I2I will move along control resistance I22 towards the right hand end thereof. As a result, less resistance will be placed in parallel with the winding H3 whereby a smaller amount of current will flow through the winding II 3, and similarly .a

greater amount of resistance will be placed in parallel with the winding H i'whereby a greater amount of current will flow through this winding. The plunger I I5 therefore moves towards the left and in so doing flexes switch arm III] to the left of its vertical position and towards the contact II2. When the temperature to which bimetallic element H9 has lowered'sufiiciently, the plunger M5 will have moved to the left far enough to till bring switch arm IIII into engagement with contact H2. When this occurs, field winding 9| is short circuited by the following circuit: from the right hand end of field winding 9|, wire IIO, wire I34, contact I I2, switch arm I I0, wire I3 I, and wire I32 to the left hand end of field winding 9|. The field winding 90 is therefore efiective to rotate its associated rotor 88 in such a direction as to cause counter-clockwise rotation of the main operating shaft 85 when viewed from the left. Such rotation of main operating shaft 85 moves the valve being controlled to a more nearly closed position and at the same time causes counterclockwise rotation of plate I05 about its pivot I05, whereby contact H2 is moved in a direction to separate from the switch arm I I0.

Engagement of switch arm III! with contact H2 also operated to place the resistance I35 in parallel with the winding Ii 3. It will be noted that the left hand end of winding I I3 or the junction between windings H3 and H4 is contin uously connected to the left hand end of resistance I35 by wires I30 and i3l. With the switch arm III! engaging contact M2, the right hand end of winding I I3 is connected to the right hand end of resistance I35 by wires M8, ltl, wire I35, contact IE2, switch arm Mil, wire IN and wire Q35. Connecting of resistance E35 in parallel with winding H3 further reduces the current flow therethrough whereupon plunger H5 tends to move further towards the left whereby switch arm M was brought firmly into engagement with contact H2. In this manner, immediately upon engagement of switch arm till withcontact N2, the contact pressure therebetween was iiishort-circuit from field winding Si is interrupted.

Field windings 98 and 9! are therefore again equally energized and further rotation of the main operating shaft ceases. Separation of contact lit with switch arm lit likewise results in breaking the connection that places resistance 335 in parallel with winding it The current flow through winding H3 is thereupon increased whereupon plunger i115 moves a small amount towards the right, thereby separating switch am He more widely from contacts i it.

It will be evident, as the temperature continues to rise, the main operating shaft 35 will be moved further and further in counter-clockwise direction as viewed from the left whereby the associated valve or other device being controlled will be correspondingly positioned. Upon a fall in the temperature to which bimetallic element iii) responds, the control contact arm iii will move along control resistance it? towards the left hand end thereof whereupon the flow of current now connected to the right hand end thereof by means of

wires

98 and 133, contact I l I, switch arm IID, wire I3I and wire I32. The field winding 9| therefore is rendered operative to rotate rotor 89 in such a direction that main operating shaft 85 rotates in a clockwise direction as viewed from the left. This motion is transmitted to the device being controlled and if the valve ID of Fig. 1 is being controlled by the main operating shaft 85, this valve thereupon opens more widely. Such rotation of main operating shaft 85*1'0- tates plate I05 about its pivot I08 in a clockwise direction.

Engagement of contact ill by switch arm IIG also connected resistance 535 in parallel with the winding H4. The right hand end of winding I I4 is connected to the left hand end of resistance I35 at all times by wires H30 and I31, and the left hand end of winding I it is now connected to the right hand end of resistance i35 by means of wire ill, wire 98, wire 2133, contact iII, switch arm i to, wire (131i, and wire M5. Placing of resistance H5 in parallel with winding H4 further reduces the current flow through winding IM whereupon plunger Hi5 tends to move further towards the right whereby switch arm 5H3 is brought into firm solid engagement with contact ii i. The main operatin shaft 35 must therefore continue with clockwise rotation until contact i it moves away from switch arm iii! when switch arm Mil is in the new position demanded by the relative energizations of windings 5 i3 and ti t.

When main operating shaft has been moved this far in clockwise direction, so that contact iii is moved from engagement from switch arm iii), the short-circuit for field winding 36 is interrupted whereupon field windings 93 and ti are again equally energized by being connected in series across the secondary so that further 1 shaft will be given further movements in a clockwise direction. Suitable limit switches may be provided, if desired, to limit the extreme movements of the main operating shaft 35 in a manner well brown in the art. it will be noted that no protective resistance has heen utilized in the shunt circuits by which the field windings 3t and are operatively deenerglzed. This is because the motor field windings are of sufiiciently high impedance to permit their connected singly across the secondary of transior" of S2. The protective resistances i223 and i2 1 are connected between windings and i and the controlling resistance {J22 prevents the com-- plete short circuiting of either of these windings 5 i3 and lit since these coils are designed so as to he of a desired special size and impedance and they should not he connected directly across the secondary of transformer 92 singly.

From the foregoing, it will be apparent that by this invention I provide a very simple arrangement which adapts itself to high production by which the contact pressure between a switch arm and an associated contact is increased upon engagement of such switch arm and contact and by which the space between such switch arm and contact is instantly widened upon separation thereof. The use of this simplified arrangement eliminates the necessity of providing auxiliary electrical devices or electro-magnetic coils and also eliminates the necessity of tapping into a portion of the opposed electrical devices or. electro-magnetic coils in the case auxiliary coils are not utilized.

It will be appreciated that the present invention is applicable to any arrangement in which a pair of contacts are slowly brought into engagement as a result of a gradual variation in the electrical current flowing to a device which controls one or more of these contacts. The two modifications herein shown therefore are to be taken as merely illustrative of two forms which the invention may take and I am to be limited only by the scope of the appended claims.

I claim:

1. In an air conditioning system, an element in control of the condition of a space to be con-.- trolled, electrical means in control of said element, a switch in control of said electrical means, a variably energizable electrical device in control of said switch, a condition responsive means in control of the energization of said device for varying the current flow thereto, and resistance means associated with said device and controlled by said switch, arranged to vary the current flow through said device, upon closure of said switch, in such manner as to increase the contact pressure of said switch.

2. In an air conditioning system, an element in control of the condition of a space to be con- 1 trolled, electrical means in control of said element, a switch in control of said electrical means, a variably energizable electrical device in control of said switch, a condition responsive means in control of the energization of said device for varying the current flow thereto, resistance means associated with said device and controlled by said switch, arranged to vary the current flow through said device, upon closure of said switch, in such manner as to increase the contact pressure of said switch, and means operated by said electrical means to cause opening of said switch.

3. In an air conditioning system, an element in control of the condition of a space to be controlled, electrical means in control of said element, a switch in control of said electrical means, a variably energizable electrical device in control of said switch, a condition responsive means in control of the energization of said device for varying the current flow thereto, resistance means associated with said device and controlled by said switch, arranged to vary the current flow through said device, upon closure of said switch, in such manner as to increase the contact pressure of saidswitch, and means controlled by said electrical means to vary the current flow through said device in a manner to cause opening of said switch.

4. In an air conditioning system, an element in control of the condition of a space to be controlled, electrical means in control of said element, a switch in control of said electrical means, avariably energizable electrical device in control of said switch, a condition responsive means in control of the energization of said device for varying the current flow thereto, resistance means associated with said device and controlled by said switch, arranged to vary the 01.11-

rent flow through said device, upon closure of said switch, in such manner as to increase the contact pressure of said switch, and mechanical connections between said electrical means and switch to cause opening of said switch.

5. In combination, reversible motor means, double circuit switching means in control thereof, a pair of oppositely acting electrical devices in control of said switching means, a controller electrically associated with said devices and arranged to vary the respeetive energizations thereof whereby to cause movement of said switching means to closed circuit positions, resistance means associated with said devices controlled by said switching means and operated to further vary the respective energizations of said devices in a direction to increase the contact pressure in saidswitching means upon closure of either of its circuits, an element to be controlled, electrical means associated with said devices to balance the energizations thereof and mechanical connections between said reversible motor means, said element to be controlled and said last-named electricalmeans.

6. In combination, reversible motor means, double circuit switching means in control thereof, a pair of oppositely acting electrical devices in control of said switching means, a controller electrically associated with said devices and arranged to vary the respective energizations thereof whereby to cause movement of said switching means to closed circuit positions, resistance means associated with said devices controlled by said switching'means and operated to further vary the respective energiz'ations of said devices in a direction to increase the contact pressure in said switching means upon closure of either of its circuits, an element to be controlled, and mechanical connections between said element to be controlled and said switching means operative simultaneously to position said element and operate said switching means to open circuit position.

7. In combination, a pair of oppositely acting electrical devices, double-circuit switching means controlled thereby and arranged to be in open circuit position when said devices are substantially equally energized and to selectively close first and second circuits when a first of said devices is energized sufiiciently more highly than a second of said devices and vice versa, a variable electrical controller associated with said devices and operable to vary the relative energizations of the same, resistance means associated with said devices rendered operable upon closure of either circuit by said switching means to further vary tions between said reversely acting electrical means, element to be positioned and variable electrical balancing means.

8. In combination, a pair of oppositely acting electrical devices, double-circuit switching means controlled thereby, a ,variable electrical controller associated with said devices and operable to vary the relative energizations of the same,

resistance means associated with said devices ren- I said switching means to further vary the energizations of said devices in a manner to increase dered operable upon closure of either circuit by the contact pressure in said switching means, reversely acting electrical means controlled by said switching means, an element to be positioned, and connections between said reversely acting electrical means, element to be positioned, and switching means.

9. In combination, a pair of oppositely acting electrical devices, a variable resistance controller electrically connected thereto and operable to vary the respective energizations thereof, a switch controlled by the cooperative action of said devices, resistance means connected to said devices and switch in a manner to increase the contact pressure of said switch by further varying the energizations of said devices upon closure of the switch, electrical means aso controlled by said switch, an element to be positioned, means to cause opening of said switch, and connections between said electrical means, element to be positioned, and switch opening means.

10. In combination, a pair of oppositely acting electrical devices connected in series across a source of power, a control potentiometer including a control resistance and a control contact movable in respect to each other, connections connecting said control resistance in parallel with the series connected electrical devices and connecting the control contact to the junction of said electrical devices, double circuit switching means controlled by the conjoint action of said electrical devices, a single resistance having one end thereof connected to the junction of said electrical devices and its other end connected to the common connection of said double circuit switching means, two-coil electrical means controlled by said double circuit switching means, connections by which said switching means respectively operatively energizes one or the other of said coils of the twocoil electrical means and places said resistance in parallel with one or the other of said electrical devices, an element to be controlled, means to open said switching means, and connections between said two-coil electrical means, element, and switch opening means.

11. In combination, a pair of oppositely acting electrical devices connected in series across a source of power, a control potentiometer including a control resistance and a control contact movable in respect to each other, connections connecting said control resistance in parallel with the series connected electrical devices and connecting the control contact to the junction of said electrical devices, double circuit switching means controlled by the conjoint action of said electrical devices, a single resistance having one end thereof connected to the junction of said electrical devices and its other end connected to the common connection of said double circuit switching means, two-coil electrical means controlled by said double circuit switching means. connections by which said switching means respectively operatively energizes one or the other of said coils of the two-coil electrical means and places said resistance in parallel with one or the other of said electrical devices, an element to be controlled, variable resistance means associated with said electrical devices and operable to vary the respective current flows thereto, and connec tions between said two-coil electrical means, element to be positioned and said variable resistance means.

12. In combination, a pair of oppositely acting electrical devices connected in series across a source of power, a control potentiometer including a control resistance and a control contact movable in respect to each other, connections connecting said control resistance in parallel with the series connected electrical devices and connecting the control contact to the junction of said electrical devices, double circuit switching means controlled by the conjoint action of said electrical devices, a single resistance having one end thereof connected to the junction of said electrical devices and its other end connected to the common connection of said double circuit switching means, two-coil electrical means controlled by said double circuit switching means, connections by which said switching means respectively operatively energizes one or the other of the coils of said two-coil electrical means and places said resistance in parallel with one or the other of said electrical devices, an element to be controlled, a balancing potentiometer including a balancing resistance and a balancing contact movable in respect to one another, connections between said balancing potentiometer and electrical devices by which the respective energizations of said devices may be varied by the balancing potentiometer, and connections between said two-coil electrical means, said element to be positioned and the balancing potentiometer.

13. In combination, a pair of oppositely acting electrical devices connected in series across a source of power, a control potentiometer including a control resistance and a control contact movable in respect to each other, connections connecting said control resistance in parallel with the series connected electrical devices and connecting the control contact to the junction of said electrical devices, double circuit switching means controlled by the conjoint action of said electrical devices, a single resistance having one end thereof connected to the junction of said electrical devices and its other end connected to the common connection of said double circuit switching means, two-coil electrical means controlled by said double circuit switching means, connections by which said switching means respectively operatively energizes one or the other of said coils of the two-coil electrical means and places said resistance in parallel with one or the other of said electrical devices, an element to be controlled, mechanical means connected to said switching means operable to move the same to open circuit position, and connections between said two-coil electrical means, element to be positioned and said mechanical means.

14. In combination, a first pair of oppositely acting electrical devices connected in series across a source of power, a controlling potentiometer including a control resistance and an associated contact, connections connecting the control resistance in parallel with the series connected electrical devices and the associated contact to the junction of said electrical devices, a first double circuit switching mechanism controlled by said electrical devices, a second pair of oppositely acting electrical devices also, connected in series across said source of power, a single resistance connected to the junction of said first electrical devices and to the common terminal of said first double circuit switching mechanism, circuit connections respectively connecting the other two terminals of said double circuit switching mechanism with the second pair of electrical devices, a second double circuit switching mechanism controlled by said second pair of electrical devices, reversible motor means controlled by said second double circuit switching mechanism, means associated with said first double circuit switching mechanism controlled by said reversible motor means and operative to cause movement of said first double circuit switching mechanism to open circuit position, and an element to be positioned also controlled by said reversible motor means.

15. In combination, a first pair of oppositely acting electrical devices connected in series across a source of power, a controlling potentiometer including a control resistance and an associated contact, connections connecting the control resistance in parallel with the series connected electrical devices and the associated contact to the junction of said electrical devices, a first double circuit switching mechanism controlled by said electrical devices, a second pair of oppositely acting electrical devices also connected in series across said source of power, a single resistance connected to the junction of said first electrical devices and to the common terminal of said first double circuit switching mechanism, circuit connections respectively connecting the other two terminals of said double circuit switching mechanism with the second pair of electrical devices, a second double circuit switching mechanism controlled by said second pair of electrical devices, reversible motor means controlled by said second aoaai to double circuit switching mechanism, a balancing potentiometer including a balancing resistance and an associated contact, connections connecting said balancing resistance in parallel with the first series connected electrical devices and the associated contact with the junction thereof, an element to be positioned, and mechanical connections between said reversible motor means and said balancing potentiometer and the element to be positioned.

16. In combination, a-pair of oppositely acting electrical devices, a switch controlled thereby, control means associated with-said devices to vary the respective energizations thereof in a manner to cause closure of said switch, an electrical mechanism, connections by which said mechanism is placed in circuit with the whole of one of said devices upon closure of said switch and in a manner to further vary the respective energizations of said devices in switch closing direction whereby closure of said switch results in an increase in the pressure between the contacts there of, electrical means controlled by said switch, and an element to be positioned controlled by said electrical means.

DANIEL G. TAYLOR.