US3694787A

US3694787A - Time proportioning electrical control device

Info

Publication number: US3694787A
Application number: US140883A
Authority: US
Inventors: Robert Eugene Emmons
Original assignee: Penn Controls Inc
Current assignee: Penn Controls Inc; Johnson Controls International Inc
Priority date: 1971-05-06
Filing date: 1971-05-06
Publication date: 1972-09-26
Anticipated expiration: 1989-09-26

Abstract

An electrical control device designed to produce a variable electrical signal proportional to the degree of change of an environmental parameter over a preselected band width. A pair of electrical contacts in a normally spaced apart relation are connected in series between a signal source and the element to be controlled so that the signal is allowed to be transmitted to the element upon the closing of the contacts. This invention operates by using a high frequency interruption of a signal current by means of a pair of opening and closing contacts. One contact is positioned relative to the other by means of an environmental sensing device responding to changes in a particular environmental parameter. The second contact is mechanically coupled to the current responsive device for effecting movement of the second contact away from the first contact when energized to provide a continuous interruption of the signal, where the ratio of the current responsive device''s on-time to off-time is proportional to the degree of change of the environmental parameter within the preselected band width.

Description

United States Patent Emmons [54] TIME PROPORTIONING ELECTRICAL CONTROL DEVICE [72] Inventor: Robert Eugene Emmons, Goshen,

Ind.

[73] Assignee: Penn Controls, Inc., Oak Brook, Ill.

[22] Filed: May 6, 1971 211 Appl. No.: 140,883

[52] US. Cl .l ..337/l24, 337/38 [51] Int. Cl. ..H0lh 71/22 [58] Field of Search ..337/38, 99, 101, 123, 124, 337/299, 300, 378

[56] References Cited UNITED STATES PATENTS 2,817,741 l2/l957 Turner ..337/99 X 2,852,640 9/1958 Lancey ..337/99 X 2,908,786 10/1959 Schleicher ..337/l0l Primary Examiner-Bernard A. Gilheany Assistant'Examiner-F. E. Bell Attorney-Johnson, Dienner, Emrich, Verbeck & Wagner [451 Sept. 26, 1972 [57] ABSTRACT An electrical control device designed to produce a variable electrical signal proportional to the degree of change of an environmental parameter over a preselected band width. A pair of electrical contacts in a normally spaced apart relation are connected in series between a signal source and the element to be controlled so that the signal is allowed to be transmitted to the element upon the closing of the contacts. This invention operates by using a high frequency interruption of a signal current by means of a pair of opening and closing contacts. One contact is positioned relative to the other by means of an environmental sensing device responding to changes in a particular environmental parameter. The second contact is mechanically coupled to the current responsive device for effecting movement of the second contact away from the first contact when energized to provide a continuous interruption of the signal, where the ratio of the current responsive device's on-time to off-time is proportional to the degree of change of the environmental parameter within the preselected band width.

10 Claims, 9 Drawing Figures PATENTEDsms m2 3 694, 78 7 SHEET 1 0F 2 fnz/enfovt I Roberi Z1 15987262 7227720725, 5?; WW @WJM M Q MW 2.

BACKGROUND OF THE INVENTION This invention relates to an electrical controldevice for providing a signal proportional to the degree of change of an environmental parameter and in particular relates to the type of electrical control devices that operate by a high frequency interruption of the signal current effected by a rapid make and break of a pair of contacts.

This invention answers the need for a reliable and economical means of providing a proportional signal current of sufficient magnitude to operate a variety of different primary controls such as valve operators, damper motors, and staging switches.

SUMMARY OF THE INVENTION This invention relates to an electrical control device for providing a variable electrical signal proportional to the degree of change of a particular environmental parameter over a preselected band width. The invention employs a pair of electrical contacts disposed in a normally spaced apart relation and adapted to be connected in series between a signal source and the element to be controlled such that the signal current is permitted to pass to the element when the electrical contacts are closed together. A sensor device responsive to variations of the particular environmental parameter being detected functions to proportionally move an actuator member. This actuator member is disposed such that it moves a first contact into engagement with the second contact whenever the environmental parameter is within the preselected band width. Upon closing the contacts, acurrent responsive device is energized causing the second contact to move away from the first contact to interrupt the signal. A continuous interruption of the signal is affected by the current responsive device by using the dimensional extension of an electrical conductor wire due to the heat generated by the signal current passing through the wire. By using an electrical conductive wire, it is possible to adjust the ratio of the on-time to off-time of the current responsive device to be proportional to the degree of change of the environmental parameter of the preselected band width.

. BRIEF DESCRIPTION OF DRAWINGS For a better understanding of this invention, reference may be had to the accompanying drawings in which:

FIG. 1 is a schematic view of one embodiment of this invention;

FIG. 2 is a schematic view of a second embodiment of this invention;

FIG. 3 is a schematic view of a third embodiment of this invention;

FIG. 4 is a schematic view of a fourth embodiment of this invention;

FIG. 5 is a schematic view of a fifth embodiment of this invention;

FIG. 6 is a schematic view of a sixth embodiment of this invention;

FIG. 7 is a seventh embodiment of this invention showing the use of the invention is a proportional thermostat;

FIG. 8 is an enlarged partial view of FIG. 7; and FIG. 9 is a front perspective view of the cantilever means used in the embodiment of FIG. 7.

FIRST EMBODIMENT There is shown in FIG. 1, the first embodiment of my invention in the form of a thermostat 10 represented schematically and having first and second

electrical contacts

12 and 14. First contact 12 is positioned relative to second contact 14 by a conventional bimetal element 16 responding to the surrounding temperature. Second contact 14 is mounted on the outer end of a spring leaf 18, which biases contact 14 away from con tact l2.

Thermostat 10 is designed to operate by means of a high frequency interruption of the signal current passing through the

contacts

12 and 14 by virtue of a continuous making and breaking of contacts. This desired interruption is effected by means of a current responsive device 20 mechanically displacing second contact 14 away from first contact 12. The current responsive device 20 uses an electrical conductive wire in the form of a length of fine wire 22 to cause this displacement by passing the signal current through the wire upon closure of the contacts to heat the wire until its length increasesby a sufficient amount to bpen the contacts. Upon cooling, the wire 22 contracts to again close the contacts and this action is repeated until the first contact 12 is repositioned by the bimetal element 16 away from second contact 14.

The dimensional excursion of the electrical conductive wire 22 is used in the FIG. 1 embodiment to open the contacts by mounting the left end 24 of the wire 22 to a fixed position and mounting the right end 26 to the spring leaf 18 such that the wire 22 is in a perpendicular relationship to the spring leaf. The spring leaf 18 biases the contact 12 towards the right,and the extension of the length of wire 22 will permit the contact 14 to move towards the right until its engagement with contact 12 is broken. The material of the wire 22 and its cross-section must be chosen with regard to the density of the signal current to provide sufficient heating to effect the necessary dimensional change of length. The total length of the wire 22 must be selected to correlate the movement of the first contact 12 by the bimetal element 16 in order to provide sufficient expansion to actuate the second contact 14 over a preselected temperature band. The phrase preselected temperature band is intended to mean the amount of change in temperature from a desired room temperature, hereinafter called the OFF temperature for thermostat 10.

To explain the operation of the first embodiment, an example will be given. Assume a fine stainless steel wire is used for the conductor 22 having characteristics that the amperage of the signal current increases its temperature by F above ambient, and that at this temperature the length of the wire increases by 4 mils. The bimetal 16 is then selected so that it will change the position of contact 12 by 4 mils in response to a change of 4 F in the ambient temperature from the OFF temperature. The thermostat condition could then change from contacts being fully closed to fully open with a room temperature change of 4 F and would be said to have a band width of 4 degrees. If then the room temperature changes 1 degree below the OFF temperature,

the

contacts

12 and 14 will be on one-fourth of the time and off three-fourths of the time since the contact 14 must only be moved 1 mil to open the contacts. If the room temperature should suddenly change 3 degrees below the OFF temperature, the

contacts

12 and 14 would then be on three-fourths of the time and off onefourth of the time. Thus it can be seen that the device being controlled is energized for a relatively long length of time if the variation in temperature from the OFF temperature is large. Thus, when the room temperature is within the proportional band of the thermostat, the amount of work done will be directly related to the percentage of the time that the current flows to provide a proportional band width.

In the above example, it should be noted that the temperature of the wire never attains 100 degr'ee rise at one-fourth ON time, but more realistically about 35 degrees or just enough to provide sufficient expansion to open the contacts. Since the opening and closing of the contacts occur at a high frequency, the wire does not cool down to ambient, but rather the wire temperature oscillates between two temperatures that provide just enough movement and force differential to move the contact structure for second contact 14.

The first embodiment schematically illustrated in FIG. 1 embodies the principles of this invention to provide a new concept in thermostatic devices designed for heating or cooling control. This new concept is embraced in the combination of the use of an energized wire for effecting a precise and predetermined amount of movement to control the effective width of the proportional band and a separate sensing device,such as a bimetal, responding to changes in the ambient temperature to adjust the relation of on-time to off-time within the proportional band.

SECOND EMBODIMENT There is shown in FIG. 2 a second embodiment of this invention comprising a thermostat 30 designed to operate with a high frequency interruption of the signal current. This embodiment operates in the same manner as the first embodiment but is designed to cover a short .temperature range by using a conventional bimetal helix 32 for changing the position of the first contact 34. The second contact 36 is secured to the outer end of a contact leaf 38 and is spring-biased towards the right by virtue of a separate spring 40. The current responsive device 42 for the second embodiment is identica to that shown in the first embodiment comprising a length of conductive wire 44 having its left end 46 mounted in a fixed position and its right end 48 fastened to the contact leaf 38. One difierence in the second embodiment from the first embodiment is that the signal current bypasses the bimetal 32 by the addition of a spring member 50 fastened adjacent contact 34, where the device to be controlled is electrically connected to its outer terminal 52.

. THIRD EMBODIMENT Referring to FIG. 3, the thermostat 54 illustrates an alternative means of mechanically interconnecting the thermal responsive electrical conductive wire 56 to the second contact 58 by using an elongated linking member 60 stretched between the approximate midpoint of the wire 56 and the contact leaf 64 adjacent the second contact 58. By virtue of this arrangement, it is possible to amplify the lineal extension of the wire 56 to move the second contact 58 by a factor of two or three times the lineal extension of the wire 56. This of course permits a much shorter length of thermal responsive wire 56 to be used in the thermostat, which is an important advantage in the design of thermostats where space limitations are always critical. An insulator 68 interconnects the left end 65 of the linking member 60 to the mid-point 62 of the thermal responsive wire 56 to prevent current flow in the linking member. The right end 66 of linking member 60 is secured to spring contact leaf 64.

The third embodiment shown in FIG. 3 has a first contact 70 positioned relative to the second contact 58 by a conventional bimetal helix 72. The current path for the signal current when the contacts 58 and 70 are closed, is through the contact leaf 64 through bimetal helix 72 and through the thermal responsive wire 56.

The operation of the third embodiment illustrated in FIG. 3 is identical to the first and second embodiments, except that the movement of the thermal responsive wire 56 is two or three times less than those of the first two embodiments for the same band width since the loading of the thermal responsive wire at right angles to its length permits two or three times the movement obtainable by the direct extension of wire lengths for the same temperature range.

FOURTH EMBODIMENT The embodiment of FIG. 4 is identical in function and operation to that of FIG. 3, but its parts are arranged in a somewhat different structural manner.

The first and second electrical contacts and 82 are supported in a normally spaced apart relation from a common terminal block 84 by means of a pair of

contact leafs

86 and 88, respectively. The first contact 80 is positioned relative to the second concept 82 by a conventional bimetal helix 90 responding to the surrounding temperature.

The thermal responsive electrical conductive wire 92 has its opposite ends 94 and 96 mounted in fixed positions and its mid-point 98 interconnected to the second contact leaf 88 by means of a linking member 100 disposed in approximate 90 degree relationship with the thermal responsive wire 92.

Current flow is prevented from flowing through the linking member 100 by virtue of an electrical insulator 102. A separate spring 106 is also connected at the midpoint 98 of the thermal responsive wire 92 to provide separate loading on the wire 92 in a direction to move the second contact 82 away from the first contact 80. A separate spring, such as spring 106, may be desirable in addition to the contact leaf 88 where a large diameter wire 92 is used to provide increased electrical current.

The path of the signal current through the thermostat 78 is between the terminal 96 and the terminal 108 to permit the signal current to pass through the thermal responsive wire 92 through contact leaf 88 and through the bimetal helix 90.

FIFTH EMBODIMENT The first four described embodiments employ the principles of this invention to provide a thermostatic device having a proportional band that uses a thermal responsive wire for a precise and predeterminable amount of movement to control the effective width of the proportional band. In these embodiments, a temperature sensing device, such as a bimetal, is used to respond to the ambient temperature and thereby adjust the relation of the on-time to off-time within 'the proportional band. As will now be illustrated, the concept of time-proportioning by using a thermal responsive wire is in no way limited to being controlled by a temperature responsive device, but may be actuated by many kinds of sensing devices such as bellows or diaphragms for pressure sensing, hair or other materials for humidity control, etc.

In FIG. 5, there is shown a pressure responsive device 1 in the form of bellows which could be either a charged thermal element for temperature actuation or connected to a pressure system for control. Actuation of the bellows 110 positions the first contact 112 relative to the second contact 114. A spring 116 opposes the movement of the bellows 110 to permit the setting of an OFF position for the FIG. 5 embodiment.

The second contact 114 is mounted on the end of a contact leaf 118 and its movement away from the first contact 112 is effected by the thermal extension of thermal responsive wire 120 in the same manner as the first two embodiments. The thermal responsive wire has its left end 122 secured to a fixed position and its right end secured to the contact leaf 118 adjacent the second contact 114.

Upon the

contacts

112, 114 closing, a signal current is passed through the thermal responsive wir'e 120 causing its length to increase slightly and allowing the spring 124 to pull the second contact 114 away from the first contact 112 to interrupt the signal current.

The pressure responsive device 110 is designed such that it will change the position of contact 112 by an even amount for a change in the environmental parameter being sensed from a desired OFF position to define a band width. The dimensional extension of the thermal responsive wire 120 is then chosen to increase in length over this band widthto selectively adjust the relation of on-time to off-time of the signal current within the proportional band in the same manner as the operation of the first four embodiments.

SIXTH EMBODIMENT Referring to FIG. 6, there is shown the use of another sensing device, in this case a hair element 130 responsive to the surrounding humidity conditions. A spring element 132 tensions the left end of the humidity of the hair element 130 to accurately position the first contact 134 relative to the second contact 136 in response to changes in the surrounding humidity.

The second contact 136 is mechanically in contact with the thermal responsive electrical conductive wire 138 in exactly the same manner as the FIG. 5 embodiment. The sensing device used to detect the particular environmental parameter, such as the hair element 130 in FIG. 6, has no influence on the operation of the thermal resp'onsive wire 138. In FIG. 6, when the signal current passes through the wire 138, it lineally extends until contact 136 under the biasing influence of spring 140 interrupts the signal current in exactly the same manner as the previously described embodiment.

It will be appreciated from the description of the first six embodiments that this invention is in no way limited to being controlled by a bimetal element but may be actuated by many kinds of sensing devices such as bellows or diaphragms for pressure-sensing, hair or other material for humidity control, etc. The time-proportioning of the thermal responsive wire and the use of the hot wire for providing a precise and predeterminable amount of movement to control the effective width of the proportional bands in combination with the use of a separate sensing device to measure a particular environmental parameter and thereby adjust the relation of on-time to off-time within the proportional bands is the heart of this invention. The thermal responsive wire provides a reliable and economical means of producing a proportional signal of sufficient magnitude to operate numerous primary controls such as valve operators, damper motors, staging switches, etc.

SEVENTH EMBODIMENT There is shown in FIG. 7, the seventh embodiment of my invention in the form of a thermostat which is assembled in a circular casing 152. First and second contacts 154 and 156 are supported in a normally spaced-apart relation by means of a pair of

spring conract leafs

158 and 160, respectively. The

spring leafs

158 and 160 are secured to a contact mounting bracket 162 (only partially shown), which is mounted on the rear wall 164 of the circular casing 152. Mounting bracket 162 is supported between a pair of mounting posts 166 carried by the rear wall 164.

First contact 154 is positioned relative to second contact 156 by virtue of a conventional bimetal assembly 168. The bimetal assembly 168 comprises a bracket 170 supported on the rear wall 164 of the casing 152 by a mounting post 172 and a bimetal helix element 174 having one end 176 fastened to the mounting bracket 170 and the other end 178 bent outwardly and attached to inner end of actuator lever 180. Referring to FIG. 7, it will be appreciated that the outer end of actuator lever 180 engages the first contact 154 as it is moved towards the right. The first and second contacts are closed together with a slight displacement of first contact 154 to the right.

As in the first six embodiments, this embodiment employs a thermal responsive wire 182 to provide a continuous interruption of the current signal by utilizing the dimensional extension of the thermal responsive wire. The thermal responsive wire 182 is mechanically interconnected to a lever 184 that is positioned to engage the second electrical contact 156 by means of a novel cantilever means 186. The cantilever means 186 permits small dimensional extensions of the thermal responsive wire 182 to be substantially amplified based on the cantilever principle. Cantilever means 186 comprises a lever bracket 188 having a mounting portion 190 and a holder portion 192. The mounting portion 190 has an opening 194 for mounting the lever bracket on a mounting post 196 extending from the rear wall 164 of the casing 152. The holder portion 192 which extends in a generally perpendicular relationship to the mounting portion 190 has a pair of opposing inwardly extending flanges 198 which frictionally grip the lower end of the lever 184. The lever 184 is firmly secured in place on the holder portion 192 by means of a rivet 200.

The opposite ends 206 and 208 of the thermal responsive wire 182 are fastened to a pair of mounting

brackets

210 and 212, which are fixedly supported on the rear wall 164 of the casing 152. The mid-point 214 of the thermal responsive wire 182 is inserted through opening 215 in the holder portion 192 and soldered to the lower end of lever 184 such that the mid-point 214 is equidistant from the opposite ends 206 and 208.

The lever bracket 188 is made from an elastic material, such as a beryllium copper alloy, to provide a constant tension force on thermal responsive wire 182. The mid-point 214 is secured to the holder portion 192 after the holder portion 192 is bent counterclockwise about the hinge or pivot point 220 to place it in a state of tension. Consequently, as the thermal responsive wire 182 is heated to expand, the holder portion 192 pivots clockwise about pivot 220 and the outer end of lever 114 swings to the right. Since the distance between the pivot point 220 and the mid-point 214 is relatively short as compared with the distance between the pivot point 220 and the outer end of lever 184, a

slight extension of the thermal responsive wire 182 will cause a relatively large movement of the second contact. 156 as it follows the displacement of lever 184 to the right.

The thermostat depicted in FIG. 7 operates on the same principle as the FIG. 1 embodiment, where the thermal responsive wire 182 provides a precise and predetermined amount of movement to control the effective width of the proportional band and the temperature sensing device responds to changes in the ambient temperature to adjust the relation of on-time to off-time within the proportional band. However, the mounting and connecting arrangement of the thermal responsive wire provides a number of advantages over the mounting arrangement of FIG. 1. One of these advantages is that the two half portions of thermal responsive element 182 are mechanically in parallel to double its mechanical strength. Another advantage is that the cantilever means 186 permits amplification of the lineal extensions of the thermal responsive wire 182 by a factor of two or three times. Consequently, the loss due to the elastic modulus of the wire is much less by virtue of the amplification to provide a more reliable and more active high frequency contactor. A thermostat constructed as illustrated in FIG. 7 has a very smooth proportioning control throughout its band width.

When the casing 152 for the thermostat 150 is enclosed by a front cover, the heat from the thermal responsive wire 182 produces a secondary effect on the bimetal helix 174. This self-heating within the thermostat can be beneficial to its purpose by apparent widening of the proportioning band when the temperature sensor is designed to open the contacts on increasing temperature. By reversing the sensor action, a wide proportion band could be narrowed if that were desirable.

A thermostat designed to utilize the apparent widening of the band is also inherently anticipating a change. An example of the heating mode application is illustrated by the lowering of the room temperature and closing of the contacts by the bimetal sensor. Upon closure, the output signal demands heat which may require a considerable period of time to reach the thermostat (transport time). Heat is immediately generated in the thermal responsive wire and accumulates within the enclosure affecting the bimetal which then "anticipates an increase in temperature of the room and shortens the amount of time of the passage of signal turns. In other words, the thermostat is time proportioning with anticipation. This can be a stabilizing characteristic of the system if the design provides just the right amount of anticipation to correct the signal and not over-anticipation to create significant droop.

The same thermostat may be used for the cooling mode with anticipation, and will operate in the limits of the same temperature band through a complete inversion of the output signal or a change of the actuating control to provide a reversal of attitude between the signal and the cooling equipment. It should be noted that a change in thermostat, such as reversal of the bimetal action or contact action to reverse its mode of operation, will not provide anticipation. In fact, the heat generated by the hot wire must be well isolated or it would tend to lock on with the result of having a wide differential.

It will be apparent from the foregoing that the use of one thermostat design for both heating and cooling modes of operation provides great versatility by using the same components with accessory items added only when required. Also in this system, the proportional band may be widened as desired by shunting the signal load to increase the current density in the thermal responsive wire. This being a temperature-current relationship, approximately a 50 percent increase in current will double the temperature span of the proportioning band. With the suggested actuator design, this shunting may be done individually on the heating or cooling terminals. The total amount of anticipation available increases with the widening of the proportioning band and therefore needs no further consideration except for the value built into the original design.

It will be further apparent that modifications and variations may be made in the control device of each of the seven embodiments without departing from the scope of the novel concepts of the present invention. It is accordingly our intention that the scope of the invention be limited solely by that of the hereinafter appended claims.

I claim:

1. An electrical control device for providing a variable electrical signal proportional to the degree of change of an environmental parameter over a preselected band width comprising a pair of electrical contacts disposed in a normally spaced apart relation and adapted to be connected in series between a signal source and the element to be controlled to transmit a signal to said element when closed together, sensor means responsive to variations of said environmental parameter to proportionally move an actuator member such that one of said contacts is moved by said actuator member into engagement with the other of said contacts whenever said environmental parameter is within said preselected band width, and current responsive means energized by the closing of said contacts for effecting movement of said other contact away from said one contact until spaced apart to provide a continuous interruption of the signal, where the ratio of said current responsive means on-time to off-time is proportional to the degree of change of said environmental parameter over said preselected band width said current responsive means including a length of electrical conductive wire which carries an energizing current upon the closing of said contacts and amplification means for moving said other contact by an amplification factor several times the dimensional extension of said wire, where the heat generated by an energizing current passing through said wire causes the dimensional extension of said wire.

2. An electrical control device as defined in claim 1, wherein said sensor means comprises a bimetal element responsive to the surrounding temperature.-

3. An electrical control device for providing a variable electrical signal proportional to the degree of change of an environmental parameter over a preselected band width comprising a pair of electrical contacts disposed in a normally spaced apart relation and adapted to be connected in series between a signal source and the element to be controlled to transmit a signal to said element when closed together, sensor means responsive to variations of said environmental parameter to proportionally move an actuator member such that one of said contacts is moved by said actuator member into engagement with the other of said contacts whenever said environmental parameter is within said preselected band width, and current responsive means energized by the closing of said contacts for effecting movement of said other contact away from said one contact until spaced apart to provide a continuous interruption of the signal, where the ratio 'of said current responsive means on-time to off-time is proportional to the degree of change of said environmental parameter over said preselected band width and where the closing of said contacts enables an energizing current to be transmitted through said current responsive means, said current responsive means including a length of electrical conductive wire and means for connecting said wire to said other contact such that dimensional extension of said wire in response to the heat generated by an energizing current passing through said wire moves said other contact away from said one contact until said contacts open throughout said band width, said connecting means including spring means to constantly urge said other contact to move away from said one contact.

4. An electrical control device as defined in claim 3, wherein said means for connecting said wire to said other contact comprises an elongated linking member secured between said other contact and the approximate mid-point of said conductive wire having its opposite ends held in stationary positions and having said linking member disposed in a substantially perpendicular relation with said wire.

5. An electrical control device as defined in claim 4, wherein said linking member is thermally insulated from said conductive wire.

6. An electrical control device for providing a variable electrical signal proportional to the degree of change of the surrounding temperature over a preselected band width comprising a pair of electrical contacts disposed in a normally spaced apart relation 1. and adapted to be connected in series between a signal source and the element to be controlled to transmit a signal to said element when together, temperature sensor means responsive to variations of the surrounding temperature 0 proportionally move an actuator member such that one of said contacts is moved by said actuator member into engagement with the other of said contacts whenever the temperature is within said preselected band width, and current responsive means energized by the closing of said contacts for effecting movement of said other contact away from said one contact until spaced apart to provide a continuous interruption of the signal, where the closing of said contacts enables an energizing current to be transmitted through said current responsive means and said current responsive means includes a length of electrical conductive wire and means for connecting said wire to said other contact such that dimensional extension of said wire in response to the heat generated by the energizing current passing through said wire moves said other contact away from said one contact until said contacts open through said band width, said connecting means including spring means to constantly urge said other contact to move away from said one contact, whereby the ratio'of the on-time of said current responsive means to its off-time is proportional to the degree of change of the surrounding temperature over said preselected band width.

7. An electrical control device as defined in claim 6, wherein said means for connecting said wire to said other contact comprises an elongated linking member secured between said other contact and the approximate mid-point of said conductive wire having its opposite ends held in stationary positions and having said linking member disposed in a substantially perpendicular relation with said wire.

8. An electrical control device as defined in claim 6, wherein said linking member is thermally insulated from said conductive wire.

9. An electrical control device as defined in claim 6, wherein said means for connecting said wire to said other contact comprises a lever pivotally mounted to provide a shorter length portion and a longer length portion, the outer end of said longer length portion being disposed to engage said other contact, spring means to urge said other contact and said outer end of said longer portion to move away from said one contact and said conductive wire being secured between a fixed point and the outer end of said shorter end portion, whereby small dimensional excursions of said conductive wire cause said other contact to move a relatively large distance in direct proportion to the ratio of the longitudinal dimensions of said shorter length portion to said longer length portion.

10. An electrical control device as defined in claim 9, wherein the ends of said conductive wire are fixedly mounted in juxtaposition and the approximate midpoint of said wire is secured to said outer end of the shorter length portion and is located equidistant from said ends of said conductive wire.

. UNIT D STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,694,787 7 Dated September 26 1972 Inventor (s) Robe rt g ne Emmons It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the title page, line 5, "Penn Controls Inc. Oak Brook,

Illinois" should be Johnson Service Company, Milwaukee,

Wisconsin Signed and sealed this ZZndiday of May 1973.

(SEAL) Attest:

EDWARD'MFLETCHERJR. i v I ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM PO-1050 (10-69) USCOMNPDC 60376.:69

UNITED STATES PATENT OFFHZE CERTWECATE 0F QQRREQTEQN Patent No. ,7 7 I Dated September 26, 1972 Inventor) Robert Eugene Emmons It is certified that error appears in the above-identified patent and that said Letters Patent are herebyeorrected as shown below:

On the title page, line 5 ,"Penn Controls Inc., Oak Brook,

Illinois" should be Johnson Service Company, Milwaukee Wisconsin Signed and sealed this 22nd day of May 1973.

(SEAL) Attest:

ROBERT .GOTTSCHALK EDWARD M.FLETCHER,JR.

Commissioner of Patents Attesting Officer USCOMM-DC 60376-P69 u.s. GOVERNMENT PRINTING OFFICE: I969 0-366-334 F ORM PO-105O (10-69)

Claims

2. An electrical control device as defined in claim 1, wherein said sensor means comprises a bimetal element responsive to the surrounding temperature.

3. An electrical control device for providing a variable electrical signal proportional to the degree of change of an environmental parameter over a preselected band width comprising a pair of electrical contacts disposed in a normally spaced apart relation and adapted to be connected in series between a signal source and the element to be controlled to transmit a signal to said element when closed together, sensor means responsive to variations of said environmental parameter to proportionally move an actuator member such that one of said contacts is moved by said actuator member into engagement with the other of said contacts whenever said environmental parameter is within said preselected band width, and current responsive means energized by the closing of said contacts for effecting movement of said other contact away from said one contact until spaced apart to provide a continuous interruption of the signal, where the ratio of said current responsive means on-time to off-time is proportional to the degree of change of said environmental parameter over said preselected band width and where the closing of said contacts enables an energizing current to be transmitted through said current responsive means, said current responsive means including a length of electrical conductive wire and means for connecting said wire to said other contact such that dimensional extension of said wire in response to the heat generated by an energizing current passing through said wire moves said other contact away from said one contact until said contacts open throughout said band width, said connecting means including spring means to constantly urge said other contact to move away from said one contact.

6. An electrical control device for providing a variable electrical signal proportional to the degree of change of the surrounding temperature over a preselected band width comprising a pair of electrical contacts disposed in a normally spaced apart relation and adapted to be connected in series between a signal source and the element to be controlled to transmit a signal to said element when together, temperature sensor means responsive to variations of the surrounding temperature to proportionally move an actuator member such that one of said contacts is moved by said actuator member into engagement with the other of said contacts whenever the temperature is within said preselected band width, and current responsive means energized by the closing of said contacts for effecting movement of said other contact away from said one contact until spaced apart to provide a continuous interruption of the signal, where the closing of said contacts enables an energizing current to be transmitted through said current responsive means and said current responsive means includes a length of electrical conductive wire and means for connecting said wire to said other contact such that dimensional extension of said wire in response to the heat generated by the energizing current passing through said wire moves said other contact away from said one contact until said contacts open through said band width, said connecting means including spring mEans to constantly urge said other contact to move away from said one contact, whereby the ratio of the on-time of said current responsive means to its off-time is proportional to the degree of change of the surrounding temperature over said preselected band width.

10. An electrical control device as defined in claim 9, wherein the ends of said conductive wire are fixedly mounted in juxtaposition and the approximate mid-point of said wire is secured to said outer end of the shorter length portion and is located equidistant from said ends of said conductive wire.