US3577066A - Electrical control system - Google Patents

Abstract

An electrical control system for controlling a function and comprising a flexible, variable resistor formed to provide a plurality of adjacent portions in heat exchange relationship with one another and adapted to move toward or away from one another, depending upon the direction of flexing of the resistor. The variable resistor is flexible axially to adjust the spacing between the adjacent portions to thereby vary the mutual heat transfer therebetween. This moves the electrical resistance of the flexible resistor to effect changes in the rate of current flow therethrough. A control means in circuit with the resistor is operative in response to said current changes to control the function.

Description

United States Patent Inventor Harold A. McIntosh South Pasadena, Calif. Appl. No. 805,138 Filed Mar. 7, 1969 Patented May 4, 1971 Assignee Robertshaw Controls Company Richmond, Va.

ELECTRICAL CONTROL SYSTEM 6 Claims, 5 Drawing Figs.

US. Cl 323/69, 323/75, 338/31, 340/233 Int. Cl G05f 3/02, GOlr 17/02 Field of Search 323/75 (H),

[56] References Cited UNITED STATES PATENTS 2,758,294 8/1956 Duncan Primary Examiner-J. D. Miller Assistant Examiner-Gerald Goldberg Attorney-Fulwider, Patton, Rieber, Lee & Utecht ABSTRACT: An electrical control system forcontrolling a function and comprising a flexible, variable resistor formed to provide a plurality of adjacent portions in heat exchange relationship with one another and adapted to move toward or away from one another, depending upon the direction of flexing of the resistor. The variable resistor is flexible axially to adjust the spacing between the adjacent portions to thereby vary the mutual heat transfer therebetween. This moves the electrical resistance of the flexible resistor to effect changes in the rate of current flow therethrough. A control means in circuit with the resistor is operative in response to said current changes to control the function. v s N.

PATENTED in 4mm sum 2 or z INVENTOR. lineup A. Mc/zvrasu llrmeA/ens ELECTRICAL CONTROL SYSTEM BACKGROUND OF THE INVENTION l. Field of the Invention The present invention relates to a control system employing 'a variable resistor.

ZJDescription of the Prior Art It has been common practice to utilize a potentiometer as a variable resistor but such a device is relatively expensive to produce and offers frictional resistance to operation. Conventional. variable resistors frequently provide irregular resistance throughout their range and many will are or spark, when operated, thus rendering them unsatisfactory for use in an explosive environment. There are no control systems known to applicant which include a variable resistor having a plurality of adjacent portions or transverse lengths disposed in heat exchange relationship with one another, with the resistor being flexible axially to change the spacing between such lengths and thereby alter the heat transfer rate therebetween to adjust the resistance of such resistor and effect the dcsired control.

SUMMARY OF THE lN'VENTlON The control system of present invention is characterized by a flexible resistor formed with a plurality of adjacent portions or transversely extending lengths disposed in heat exchange relationship with one another whereby axial flexing of the resistor adjusts the spacing between such lengths to alter the rate of mutual heat exchange between such lengths to change the electrical resistance of the resistor and effect the desired control.

An object .of the present invention is to provide. a control system of the type described wherein the resistor may be varied without frictional resistance or danger of arcing.

Another object of the invention is to provide a control system as described wherein the resistor exhibits uniform increments of resistance change.

' Still another object of the present invention is to provide a control system of the type described which includes a multimetallic thermostatic blade for flexing the resistor in response to temperature changes to operate a temperature change apparatus. 4

A further object of the present invention is to provide a control system of the type described which includes a second variable flexible resistor connected in series with the first resistor, and with flexing-means connected between the two resistors whereby collapsing of one of the resistors to increase its resistance extends the other of the resistors to decrease its.resistance.

Yet another object of the present invention is to provide a control system of the type described wherein the variable resistor is in electric circuit with an electric motor and is mechanically coupled with a governor thereof, such governor being responsive to the speed of the electric motor to axially collapse and extend the resistor to vary current flow therethrough and thereby control the motor speed.

These and other objects and advantages of the present invention will become apparent from a consideration of the following detailed description when taken in conjunction with the accompanying drawings.

DESCRIPTION- OF THE DRAWINGS the control system ofthepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FlG. I, the control system S is particularly adapted to act as a thermostat to control the temperature of an environment and includes an elongated, flexible variable resistor, generally designated 11, which is formed with a plurality of adjacent portions or transversely extending lengths 13 disposed in heat exchange relationship with one another.

7 An elongated thermostatic blade 15 is disposed in the environment which is to be temperature controlled, and has its free end connected to the lower end of the resistor 11 whereby heating and cooling of such blade will flex the blade to expand and contract the resistor 11. This alters the mutual heat exchange between the lengths 13 to thereby change the resistance of the resistor 11 and vary the current flow through an operator L for controlling a temperature change apparatus (not shown).

The resistor 11 is made of a material possessing the property of experiencing a relatively high change in resistance for a relatively small change in temperature. That is, the material is characterized by a high coefficient of temperature-resistance change. Pure nickel exhibits this characteristic, as do the materials sold under the trade names Balco" and Hytempco."

Theresistor 11 may be in the form of a helical coil wherein the convolutions of wire are in heat exchange relationship with one another. The rate of mutual heat exchange is altered by elongating or shortening the helix because this changes the distance between the adjacent convolutions. Other resistor structures in which portions thereof are formed or reversely formed for location in adjacent, heat exchange relation, will suggest themselves to those skilled in the art. All such variations are within the scope of the present invention, it being important only that flexing or deformation of the resistor 11 result in an alteration of the heat exchange relation of adjacent portions of the resistor 11 and thereby effect the electrical characteristics of such adjacent portions.

The resistor ll, motor L and input terminals to the circuit are. connected in series by leads 17, I9 and 20.

In operation of the control system S, current is applied to the input leads l7 and 20 causing current flow through the resistor 11 to effect mutual heating between the adjacent portions or transverse lengths I3. Such mutual heating causes the resistance of the resistor 11 to increase, thereby causing a reduction in current flow. This decreases the self-heating, allowing more current to flow, thereby increasing the selflieating, and so on until equilibrium is reached.

The'system is adjusted so that as long as the environmental temperature remains within a selected range, the motor L remains inoperative. When the environmental temperature becomes sufficiently cool to warp the thermostatic blade 15 downwardly toward its broken line position, the resistor 11 is expanded axially. This spaces the lengths 13- farther apart, decreases the mutual heating thereof, and thereby increases the current flow-to the operator L sufficiently to operate it and adjust a damper (not shown) to increase the heat input to the environment. When the environment has been heated sufficiently to return to its equilibrium or solid line position, the resistor 13 is sufficiently collapsed that its increasedself-heating reduces the current flow to the motor L to such a low level that the motor L is inoperative.

The control system-S shown in FIG. 2 incorporates avariable flexible resistor L1" as one leg of a Wheatstone bridge, generally designated 25, to serve as a sensor. Again, one end of the resistor 11 is coupled with a thermostatic blade 15 for selectively varying its resistance. A secondleg of the bridge 25 is formed by an adjustable resistor 27, and a third:leg is formed. by a calibration resistor 29. The fourth leg of the bridge is formed by aresistor 31. Input to the bridge 25 is provided through leads 33 and 35 which are connected to respective.

bridge nodes 37 and 39. The output from the bridge 25 is connected to an electric motor (not shown).throughleads 41 and 43. The motor is operable to, for example, operate a hot and coldair distribution damper.

The 'system S is operated by applying current tothe input leads 33 and 35. When the bridge 25 is balanced, there will be essentially no current flow in the output leads '41 and 43. However, when the environmental temperature cools sufficiently broken line position. In this position there will be sufl'tcient increased mutual heating between the lengths 13 of the resistor that its increased resistance causes the bridge 25 to unbalance and provide current in the output leads 41 and 43. This output current is used, for example, to drive a damper operator (not shown) to increase the heat input to the environment. This, in turn, heats the blade 11 and causes it to return to its relaxed or equilibrium position.

The control system S" shown in H6. 3 includes a flexible variable resistor 11 having one end connected to an adjustment stud 51 and the other end to the plunger 53 of a centrifugal type of governor 55 which is mounted on the drive shaft 57 of a shaded-pole-type motor 59. The stud 51 is formed with apivotal ball bearing joint 54 which provides for rotation of the stud 51 without rotating the resistor 11. Also, the lower end of the stud 51 is electrically insulated from the resistor 11 by an insulator 56. The adjustment stud 51 has a selector knob 60 mounted on its projecting end. The governor plunger 53 is formed with a pivotal joint 62 which enables the governor 55 to rotate without rotating the resistor 11. The resistor 11 and motor 59 are connected in series by leads 61, 63 and 65.

in operation of the speed control system S", a current is applied to the input leads 61 and 65. The electric motor 59 is energized and rotates the governor 55, whichcauses the variable resistor 11 to collapse and increase mutual heating between the lengths 13. This increases the resistance of the re sistor 11 and decreases the current flow to the motor 59 until the equilibrium or set speed is reached. The set speed may be adjusted by turning the speed control knob 60 to adjust the nonnal degree of collapse of the resistor 11.

The system 8'' shown in FIG. 4 incorporates a divided circuit which includes a pair of variable flexible resistors 11 and 1 1' which form two legs of a bridge, generally designated 71, and which are both connected to a thermostatic blade 15. The third and fourth legs of the bridge 71 are formed by coils 73 and 75. The opposite ends of an arcuate armature 77 of a magnetically operated switch, generally designated 79, are moveable through the central openings of the coils 73 and 75,

. respectively. The switch 79 includes a pair of contacts 81 and 83 disposed on opposite sides of an electrically conductive arm 85 which is pivotally mounted at 87.

A pair of parallel connected operators 91 and 93 are connected in series with the respective contacts 81 and 83 by respective leads 95 and 97.

Current is supplied to the system 8'' through a pair of leads 101 and l03, the lead 101 being connected with the bridge node 102 between the resistors 11 and 11' by means of a lead 105. The lead 101 is also connected to one terminal of the respective operators 91 and 93 by means of a lead 107. The other input lead 103 is connected with the'bridge node 87 between the coil 73 and 75 and provides current to the pivotal switch arm 85. 4

In operation of the system S' of FIG. 4, current is applied to the input leads 101 and 103. As long as the thermostatic blade remains'in the neutral, solid line position shown. the switch 79 remains open, thus rendering the operators 91 and 93 inoperative. When the thermostatic blade 15 cools suiticlently to warp upwardly to its broken line position, the upper variable resistor 11 is collapsed to its broken line position and the lower variable resistor 11' is stretched to its broken line position. This increases the self-heating of the resistor 11 and decreases the self-heating of the resistor 11.

Increasing the self-heating of the resistor 11 decreases cur- 1 rent tlow therethrough and also through the series connected coil 75. Decreasing the self-heating of the resistor 11' increases current flowtherethrough and also through the series connected coil 73. The cooperative action of the coils 73 and 75- upon the opposite ends of the armature 77 pivots the switch arm 85 clockwise. The arm 85 makes contact with the contact 83, which actuates the operator 93 and opens a damper (not shown) to admit heated air to the environment. When the environment becomes sufficiently warmed to heat the thermostatic blade 15 and cause it to assume its original solid line position, the operator 93 will be rendered inoperative, thus discontinuing the call for heat.

When the thermostatic blade 15 is cooled below a selected temperature range, it will warp downwardlyvtocollapse the variable resistor 11 and stretch the resistor 11. This increases self-heating of the resistor 11 and decreases self-heating-of the resistor 11. These changes in self-heating decrease current flow through the resistor 11' and the coil 73 and increase current flow through the resistor 11 and the coil 75. This causes the switch arm 85 to rotate counterclockwise, engaging the contact 81 and actuating the operator 91. This actuates, for example, an air conditioner to cool the environment. When the thermostatic blade 15 is cooled sufficiently to assume its original solid line position, the switch 79 is opened, rendering the operator 91 inoperative.

The control system shown in FIG. 5 includes a modulating valve V having an inlet chamber 111 and an outlet chamber 113. The inlet chamber 111 is formed with an outlet 115 which communicates pressure to the underside of a pressure responsive diaphragm 117. A poppet 121 is carried centrally on the diaphragm 117 and selectively seats against an inlet 123 to the outlet chamber 113.

A conduit 127 leads from the inlet chamber 111 and terminates in an inlet port 131 to a control chamber 133 formed above the diaphragm 123. An exhaust conduit 135 leads to the outlet chamber 113 and forms an exhaust port 137 confronting the inlet port 131 and spaced therefrom.

A horizontally disposed cylindrical plug 141 is carried from pivotal actuating element 143 and has its opposite ends tapered to conical points for selective engagement with the respective ports 131 and 137 to selectively block flow therefrom. The actuating element 133 is carried from a pivot pin 147 and includes a disc 149 on its upper end which is disposed between a pair of opposed thermostatic blades 151 and 153. The multimetallic blades 151 and 153 are formed from a single multimetallic strip which is bent back on itself and is carried on its upper end from a pin 155 that is biased upwardly by a coil spring 157, vertical positioning of such pin being controlled by an adjustment set screw 159.

Carried from the bonnet 163 of the valve V are a pair of vertical tubes 165 and 167 disposed on opposite sides of the actuating element 143. Telescoped into the tubes 163 and 165 are heat motors 167 and 169 which are in a bridge circuit with variable resistors 11 and 11'. The heat motors 167 and 169 are, connected together on one end and are connected with a power source by means of a lead 171. The proximate ends of the variable resistors 11 and 11 are connected to one end of an electrically conductive thermostatic blade 173 which acts as a temperature sensor and has its opposite end connected to said power source by means of a lead 175.

The valve V is particularly useful in controlling fluid to a hydraulic heating or air-conditioning system. Operation of the valve V will be described for controlling the flow of hot fluid to a heater in response to the temperature of the environment being controlled. The thermostatic blade 173 is disposed in said environment and as long as the environment stays above the set temperature the blade 173 will remain heated and the lower end thereof flexed to the right thus maintaining the re sistor 11' collapsed and the resistor 11 expanded to thereby decrease the current flow through the resistor 11' to deliver less current to the heat motor 169 while increasing the current through the resistor 11 and to the heat motor 167. increased current to the heat motor 167 will provide additional heat to flow'from the exhaust port l33and admitting flow from the inlet port 137. This will enable the pressure in the control chamber 133- to build up to press the diaphragm 117 downwardly to maintain the poppet 121 seated on the port When the environment cools below the set temperature thus cooling the blade 173 and flexing its lower extremity to the left, the variable resistor 11' will becontracted and the resister 11' expanded to reduce current through the heat motor 167 and increase the current flow through the heat motor 169.

Such current change will cause the motors 167 and 169 to' cool the blade and heat the blade 153 thereby flexing the lower ends of such blades to the right to cause the actuator 143 torotate clockwise thereby'blocking flow from the inlet port 131 and admitting flow out the exhaust port 137. The

pressure will then be exhausted from the control chamber 133 to enable the pressure under the diaphragm 17 to raise it thus unseating the poppet 121 to admit flow out the flow port 123 to the heater (not shown). It will be noted that the degree to which the inlet port 131 is blocked is-dependent on the flexing of the sensing blade 173 thereby providing flow of hot fluid to the heater (not shown) in proportion to the environment temperature drop-below the set temperature. This provides for relatively steady state operation of the valve V without full open and closed cycling under normal conditions.

From the foregoing it will be apparent that the control system of the present invention provides an economical and exchange relationship and flexible for movement toward and away from one another to adjust said heat exchange relationship, the electrical resistance of said portions being temperature responsive whereby current flow therethrough is responsive to the temperature thereof;

means for moving said portions toward and away from one another to adjust the proximity and mutual heat transfer therebetween whereby the electrical current passing through said electrical resistance means is correspondingly adjusted; and

means in circuit with said electrical resistance means for applying said electrical current to an apparatus for operation of said apparatus.

2. An electrical control system as set forth in claim 1 that includes:

a bridge circuit including said variable resistor.

3. An electrical control system as set forth in claim l-that includes:

a divided circuit incorporating said first-mentioned variable resistor and including a second flexible variable resistor formed with a plurality of transversely extending lengths disposed in heat exchange with one another, said second resistor being characterized in that minor changes in temperature cause the electrical resistance in said lengths to change, said first and second variable resistors having their respective one ends coupled together and said flexing means being connected to said one ends whereby operation of said flexing means to contract said first-mentioned resistor and increase the mutual heating between its lengths will expand said second resistor and decrease the mutual heating between its lengths.

4. An electrical control system as set forth in claim 1 that is adapted to control a temperature change apparatus in response to changes m the environmental emperature and wherein:

Claims (6)

1. An elEctrical control system comprising: electrical resistance means having portions in heat exchange relationship and flexible for movement toward and away from one another to adjust said heat exchange relationship, the electrical resistance of said portions being temperature responsive whereby current flow therethrough is responsive to the temperature thereof; means for moving said portions toward and away from one another to adjust the proximity and mutual heat transfer therebetween whereby the electrical current passing through said electrical resistance means is correspondingly adjusted; and means in circuit with said electrical resistance means for applying said electrical current to an apparatus for operation of said apparatus.

2. An electrical control system as set forth in claim 1 that includes: a bridge circuit including said variable resistor.

3. An electrical control system as set forth in claim 1 that includes: a divided circuit incorporating said first-mentioned variable resistor and including a second flexible variable resistor formed with a plurality of transversely extending lengths disposed in heat exchange with one another, said second resistor being characterized in that minor changes in temperature cause the electrical resistance in said lengths to change, said first and second variable resistors having their respective one ends coupled together and said flexing means being connected to said one ends whereby operation of said flexing means to contract said first-mentioned resistor and increase the mutual heating between its lengths will expand said second resistor and decrease the mutual heating between its lengths.

4. An electrical control system as set forth in claim 1 that is adapted to control a temperature change apparatus in response to changes in the environmental temperature and wherein: said operator means is formed by a multimetallic blade.

5. An electrical control system as set forth in claim 1 that includes: adjustment means coupled with said variable resistor for adjusting the normal flexing thereof.

6. An electrical control system as set forth in claim 1 that is adapted to control said apparatus in response to a control parameter and wherein: said means for moving said portions is responsive to said control parameter to effect said movement.

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