US2452622A

US2452622A - Heating pad

Info

Publication number: US2452622A
Application number: US668802A
Authority: US
Inventors: Youhouse Joseph
Original assignee: Casco Products Corp
Current assignee: Casco Products Corp
Priority date: 1946-05-10
Filing date: 1946-05-10
Publication date: 1948-11-02
Anticipated expiration: 1965-11-02

Description

J. YOUHOUSE Nov. 2, 1948.

HEATING PAD Filed May 10, 1946 F4 1 INVENTOR. Jaye wk Yozmou-j'e BY fipm ATmRN s' Patented Nov. 2, 1948 UNITED STATES PATENT OFFICE HEATING PAD Joseph Youhouse, Fairfield, Conn., assignor to Casco Products Corporation, Bridgeport, Conn., a corporation of Gonnecticut Application MayilO, 1946, Serial No. 668,802

15 Claims.

1 This invention relates to electric heating pads of the type having a plurality of different selectable heats. The present application is a continuation in part of my copending application Serial Number 642,938, filed January 23, 194.6, and entitled Electric heating pad.

In a prior type of heating pad having three fixed heats, low, medium and high, an organization was employed which included a control thermostat located in the jacket of the pad close to the heating element, and included a threepoint selector switch in the supply cord of the pad, the said switch having two resistor elements connected in series, the outer or remote ends of the elements being joined respectively to the outer contacts of the switch, and the common connection of the elements joining with the middle switch contact. This prior pad was found to be generally satisfactory in operation, but according to the circuit and organization employed, in order to obtain a very low pad heat and a considerable spread or range between the low and the medium and high heats of the pad which was found to be desirable, the resistor elements in the switch, which were wire wound, had to be of relatively high ohmage. Because of the small space available in the switch for the resistor elements, this presented a problem since room was not available to take resistors of very high ohmage, and as a result a compromise was effected between the ohmage of the elements and the spread or range between the heat settings of the pad. Also, in this prior pad, one or both of the resistor elements produced heat in the switch during the low and medium settings of the latter, which settings are normally in frequent use. While this heat was not sufiicient to cause a dangerous condition, it resulted in the switch becoming warm to the touch, giving rise to doubt in the mind of a user as to the operativeness of the pad, and this warmth was evident unless the pad was used solely for high heat, wherein the resistor elements were not energized.

The present invention overcomes the difficulties enumerated above in connection with the prior type of heating pad. In accomplishing this, a simple and novel organization is provided wherein, for the low heat setting of the selector switch of the pad, the resistor element or elements in the switch are not in use, being disconnected and unenergized. According to the circuit employed, for the low heat switch setting, the entire current which is consumed passes serially through the heater for the thermostat and through the pad coils, producing a high heat in contacts.

the thermostat and resulting in the pad being maintained at a low temperature, herein termed low-low," which is considerably below the low setting of the prior type pad, and provides a distinct advantage in situations where low temperatures are desired. As a consequence, also, the spread or range between the low, and the medium and high settings of the pad of the present invention is considerably greater than the spread or range between the corresponding settings of the prior pad, and these results are all achieved without resorting to resistors of high ohmage in the selector switch of the pad.

In addition to the above advantages, the operation of the pad is such that the heating of the switch casing is generally reduced and is less n0- ticeable. This is because current is made to pass through the resistor element or elements of the switch only for the medium or intermediate settings of the latter. For both the high and low settings of the switch, which are frequently used, the resistor means is not energized. Thus, the switch casing is on the average cooler and less likely to be noticeably warm to the touch.

In one specific embodiment of the invention illustrated herein a three-point fan-blade selector switch is employed, and but a single resistor element of relative low ohmage is provided, connected between one of the outer contacts of the switch and the middle switch contact. The selector switch has a two-arm fan blade which when set in one position spans one pair of adjacent contacts of the switch, and when set in another position spans the other pair of adjacent The switch blade may be also so positioned as to engage solely the first outer contact of the switch.

According to the circuit provided, the energizing current may be made to pass serially through the thermostat heater, thermostats and heating coils of the pad without being diverted either in whole or in part through the resistor in the selector switch. This condition is effected by the lowest setting, marked low-low of the selector switch, and results in a relatively low pad heat substantially lower than that in the prior pads of this type, and considerably removed from the range of the medium and high pad heats, without resorting to high ohmage resistors in the selector switch. When the switch is set on medium, the resistor element of the switch is shunted across the thermostat heater, and a part of the current is thus diverted from the heater by the resistor element, causing the heater to operate at a lower temperature, thereby increasing the pad temperwire ature. For the high setting of the selector switch, the energizing current does not pass through the resistor element of the switch at all, nor through the thermostat heater of the pad, but instead is conducted solely through the pad thermostats and the heating coils of the pad.

In another embodiment of the invention, comprising a four-heat pad, the selector switch has an additional contact, which is interposed between the first or low-low and the second or medium contacts, and has an additional resistor element connected between the additional contact and the immediately following or succeeding contact. By this organization an additional setting or heat of the pad is obtained, located between the low and medium pad heats. Due to the fact that a substantial spread or range exists between the low-low and medium pad heats, the inclusion of this fourth heat; which is termed herein a low heat, is of advantage since it provides for finer adjustment of the pad temperature. r

.In still another embodiment of the invention the heat control switch does not have individual contactsbut instead a continuously variable resistor element, preferably of an ohmage equivvious resistor-controlled pads.

alent to the combined ohmage of the two resistor elements of the four-heat switch of the second embodiment, above. The organization of the switch with the continuously variable resistor element is such that current may be passed through the switch-either directly to the thermostat heater, or to the heating coils of the pad without being diverted either in whole or in part through the resistor element of the switch. Thus,

a wide spread is obtained between the low-low,-

and the high heats of the pad without the use of extremely high ohmage in the switch resistor,

and also a large number of graduated heats may beobtained in the pad, located between the range of the low heat of the four-heat pad and the high heat of the latter, providing for extremely fine adjustment of the pad temperature.

Other features and advantages will hereinafter appear. 7

In the accompanying drawings: Figure 1 is a diagrammatic representation of a heating pad made in accordance wtih one embodiment of the invention.

Fig. 2 is a diagrammatic representation of a switching control for use with the pad proper of Fig; 1, illustrating another embodiment of the different locations respectively a saftey thermo-' static switch l2 and a control thermostatic switch [3. The thermostatic'switch [3 has a heater [4 associated with it, one end 15 of the heater being connected with one terminal of the switch l3 and'also connected with a wire [6 passing through a supply cord ll leading from the jacket ID. The other end it? of the heater M is connected to a cord l1.

The other terminal 20 0f the control thermostat l3 is connected by a wire 2! with one terminal 22. of the safety thermostat l2, and the remaining terminal 23 of the safety-thermostat I9,--also extending through the supply is connected by a wire 24 with one end 25 of the heating element 1 I. The opposite end 26 of the heating element is in turn connected with a line wire 21 passing through the supply cord l1.

According to the present invention a novel resistor-type control, mounted in a single casing, is provided in the supply cord H, the said control enabling the heating coils H of the pad to be operated at a low temperature which is substantially less than the low temperatures of pre- Also, the control is so arranged that the casing thereof is on the average cooler than in prior pads having resistortype controls, and is therefore less likely to be noticeably warm to the touch.

The control comprises, in the embodiment of Fig. l, a continuously variable resistor 28 which is mounted in a switch casing diagrammatically indicated ,at 29 in broken outline. The resistor 28 comprises a resistance element 39 having one end secured to a contact and terminal 31, the other end 32 of the element being free or unconnected. A movable contactor 33 is provided for engagement with the element 30, the said contactor being slidable on the element so that the the resistor 28 has a contact bar 38, the said bar making electrical connection with the contactor throughout the engagement of the latter with the resistor element 30, and also connecting with the contactor when the latter is in the position indicated at 35, located beyond the free end 32 of the element and out of engagement therewith. A .dead stationary contact 37 is shown at this position.

Also, the resistor 28 is so constructed that the contactor 33 may be moved out of engagement with the bar 34, as shown -by the position the contactor occupies in Fig. 1, (represented by full lines). 1

Connections of the control are as follows: The wire, I .9 in the cord ii is connected with the contact bar .3 3 of ,the resistor 28, and the wire [6 of the cord is connected with the terminal 3! of the resistor. The wire 21 of the cord ll passes through the casing 29 and constitutes a supply line'forthe heating pad, and a second supply line 381s connected with the movable contactor 33.

For purposes of illuminating the switch or control unit, a gaseous glow lamp 39 is mounted in the casing 29 and connected through a series current-limiting resistor ii] to the contact bar 34, and through a wire 3! to the line wire 2-1.

According to the above organization provided by the invention, a very low pad heat is obtainable when vthe contactor 33 is in the position 36 indicated in Fig. 1, the said heat being termed herein a low-low heat, since it is substantially less than the low heat of prior pads having resistor-type controls. For this position of the conta'ctor 33 the energizing current passes seriinent 3B, the said element is shunted across the thermostat heater l4 and diverts a part of the current from the latter. As a result, the heater l4 operates at a somewhat lower temperature causing the control thermostat is to respond so as to produce a heat in the coils II which is higher than the low-W heat. This higher heat is termed herein a low heat, since it is the same as the corresponding low heat of prior pads having resistor-type control switches.

As the contactor 33 is moved along the resistance element at toward the high position wherein it engages the contact iii, more and more of the current will be diverted from the heater I4 of the control thermostat 53, causing a lesser heating of the heater and a consequent higher temperature in the pad coils i When the contactor 33 engages the contact 3! at the high position, the thermostat heater 94 will be short circuited and substantially no current will pass through it. For this condition, the thermostatic switch 53 responds solely to heat from the coils l l of the heating pad and the latter are therefore maintained at their highest operating temperatures.

When the contactor 33 is in the off position, it does not engage the contact bar 34, and the pad is thus deenergized, since no current flows through any of the circuits.

It will be obvious that the lamp 3% is also deenergized for the off position. of the contactor 33, and is fully energized for the remaining, energizing positions of the contacior, thereby providing a visual indication at the control when the pad circuits are energized.

It will be seen that, by the above organization, the heating coils Ii of the pad Ed may be controlled to produce a ver low heat in the pad without resorting to the use of extremely high resistance in the element 3!), since the said element is not energized for the low-low setting of the control. Thus, there is not present the problem of providing a resistance element of extremely high ohinage for use in the constricted space within the switch casing 3-29, which problem has heretofore defeated attempts to produce a very low heat in pads of this type, and to produce a wide spread between the lowest and highest heats of the pad.

Moreover, due to the fact that for the low-low and high settings of the control, the resistance element 35) thereof is not energized, no heat is produced within the switch casing 29 for these set-- tings. It is only for the settings of the control located between the low-low and the high position that the element 33 is energized, in contradistinction to the prior heating pads wherein the element is energized for all except high settings. As a consequence, on the average, the heat produced in the switch casing 29 is less, and the casing is therefore generally cooler to the touch than was heretofore possible to achieve.

Another embodiment of the invention is illustrated in Fig. 2, wherein a resistor-type control is provided the form of a selector switch which has predetermined settings representing substantially difierent degrees of heats in the pad, the said settings being chosen to provide fairly substantial steps in contra-distinction to the continuously variable control of Fig. 1.

The selector switch 42 shown is of the threepoint fan blade type, and the control incorporating the switch has but a single resistor element 43, the said element bridging adjacent contacts 44, 45 of the switch. The two

outer contacts

44 and 46 of the switch are connected respectively to the wires I5 and IQ of the supply cord I! so as to be bridged by the thermostat heater I4.

The selector switch 42 includes a fan blade 41' having contact-engaging portions 48 and 49 shaped so that they can bridge either pair of adjacent contacts, 46, 45 or 45, 44. Also, the blade 4'! may be positioned so that solely the portion 49 thereof engages the contact 46, or so that none of the switch contacts are engaged, the latter position being shown in the figure.

The supply wire 38 for the pad is connected with the switch blade 47, and the supply wire 21 passes through the switch casing 50 and into the body I 0 of the pad.

When the blade 41 is in the oif position wherein the portions 48 and 49 do not engage any of the

contacts

46, 45 or 44, the heating element H is not energized, and the pad is in the cold condition. When the blade 4'! is moved counterclockwise to low position, the portion 49 thereof engages solely the switch contact 46 and current flows from the line wire 38 through the wire 19, thermostat heater l4, thermostat l3, wire 2!, safety thermostat 12, wire 24, and through the heating element II to the return supply wire 21.

This energizes the heating coils ll of the pad so that the heating thereof is in the low-low range, similar to that described in connection with Fig. 1.

When the switch blade 41 is shifted to the medium setting, the portions 48 and 49 of the blade 41 engage the switch contacts 45 and 46. Current thus flows through both the resistor 43 and the thermostat heater M, which are now in parallel, and thence through the thermostats l3 and i2, and the heating element H to the line wire 2?. By this connection less current flows through the thermostat heater I4 than for the low-low setting of the switch, and consequently the thermostat I3 is operated so as to maintain the heating element and pad at a higher tem perature, which is termed the medium heat of the pad.

When the switch blade 4'! is rotated still further counterclockwise so that the portions 48, 49 thereof engage the switch contacts 45, 46, respectively, the thermostat heater I4 is cut out of the circuit, and the resistor 29 is shunted out, and current flows through the wire it directly through the thermostat i3, and thence through the thermostat i2 and heating element 1 i to the return supply wire 27. For this setting of the switch, the control thermostat E3 is operated solely in response to the heat from the heating element H, and consequently the thermostat operates to maintain the pad at a still higher temperature than that provided by the previous switch setting. This higher temperature is termed the high heat of the pad.

Another embodiment of the invention is illustrated in Fig. 3. The control 5i shown herein is similar in a number of respects to the control 42 shown in Fig. 2, and therefore like parts have been given like characters, However, in the con trol 5! the fan blade 5m has three arms 51b, 5lc and and a fourth stationary contact 52 is provided, located between the stationary contacts 45 and 43. Also, a second resistor element 53 is connected between the contact 52 and the contact 45. A fourth position is thus added to the control, this position being termed low since it corresponds with the low heat of prior pads arteries 7 of th'is'type, and this position is indicated at 54 in the figure.

The provision of the fourth setting, as incorporated in the control l, is of distinct advantage in providing for a finer adjustment of the pad heat, in view of the fact that asubstantial spread may exist between the low-low heat of the pad and the medium heat of the pad, as determined by the value of the resistor element 13.

It will be understood that when the blade to; is in the off position shown in the figure, no current will flow through the pad circuits and the pad will thus be cold. When the blade is shifted so that the arm Eld thereof en ages the stationary contact 45, current will flow through the thermostat heater it without being diverted, and this will cause the pad to operate at the low-low heat. When the blade 55a is. shifted to the low setting, .the arms Elc and did will respectively engage the contacts and 52, and current'will divide between the thermostat heater I l and the series-connected resistors 55 and t3. This reduces thecurrent of the heater id and causes the thermostat i3 to operate the pad at the standard low temperature.

As the switch blade 5m is shifted to the medium setting, the arms 5H3, die and Md of the blade will respectively engage the contacts i6, 52 and 45. This short circuits the resistance element 53, and causes the energizin current to be divided between the element %3 and the heater l4, resulting in a still lesser heat of the latter, and a still higher pad temperature. In the high setting of the fan blade Elia, the resistance elements 43 and as will be shunted out, and the heater i l will also be cut out of the circuit. Current will thus flow serially through the thermostats l3 and E2 of the pad, and through the pad coils H, and the heat from the latter will be the sole means for actuating the thermos at it. As a consequence the pad coils will be maintained at their hottest operating temperatures.

By the organization provided in Fig. 3 a considerable spread or range is possible between the low-low and the high heats of the pad, and the said range is so divided that two intermediate heats are obtainable. This not only provides a desirable overall choice of heats, but also so enables the pad to be operated at a very low temperature, such as may be indicated in certain forms of treatments.

Variations and modifications may be made within the scope of this invention and portions of the improvements may be used without others.

I claim:

1 In a heating device, a thermostatic switch; a heater for the thermostatic switch; a resistor, said heater and resistor at one point each having a common connection; a pair of current supply wires; means for selectively connecting one of the current supply wires either solely to another point on the heater, or to the said other point on the heater and simultaneously to another point on the resistor, or to the said common connection of the resistor and heater; and electric heating means connected. with the said common connection of the resistor and heater and with the other current supply wire, the said thermostatic switch controlling'the circuit of the said heating means.

2. In a heating device, a thermostatic switch; a heater for the thermostatic switch; a resistor, said heater and resistor at one point each havin a common connection; a pair of current supply wires; means for selectively connecting one ofthe current supply wires either solely to another'point on "the heater, "or toithe said other point on the heater :and simultaneously .to another'point on the resistor, or to the said other point on the heater'and simultaneously to :still another point on the'resi'stor, or to thesaid common cc-nnection'of the resistor andheaterpand electric heating "means connected with the said common connection'of the resistor and heater, and'with the other'current supply wire,'the said thermostatic switch: controlling .the circuit .ofzthe said heatin means.

3. In a heating device, a heating element; .a thermostaticiswitchcontrolling the circuit of the heating element; :a heater for thexthermostatlc switch; a resistor, said heating element, heater and resistor having ends connected with'each other, constituting a common connection; means for-connecting one leg of a'current supply-With the other end of the heating element; andmeans for selectively connecting the other leg of :the current supplyeither'solely to the other .end of the heater for the switch, or simultaneously'to the other ends of both the resistor and the heater for the switch, or to the other end of the heater and simultaneously to an intermediate point on the resistor, o'r'to thesaid common connection of the heating element, resistor, and heater for the switch.

4. In a heating device, a'heating element; a. thermostatic switch controlling the circuit of the heating element; a heater for the thermostatic switch; a resistor, said heating element, heater and resistor having ends connected with .each other, constituting a common connection; means for connecting one leg of a current supplywith the other end of the heating element; and means for selectively connecting the other leg of the current supply either solely to the other end of the'heater for the switch, or to the otherends of both' the resistor and the heater for the switch, or to the other end-of the heater and simultaneouslyto'any of a plurality of intermediate points on the resistor, or to the said common connection of the heating'element, resistor, and heater for the switch.

5. In a heating device, a'heatin'g element; a thermostatic switch controlling the circuit 'of the'heating element; a heater for the thermostatic switch; a resistor, said heating element, heater and-'resistor'having ends connected with each other, constituting a common connection; means for connecting one leg of a current supply with the other end of the heating element; and means for selectively connecting the other leg of the current supplyeither solely to the other end of the heater for the switch, or to'the other ends of both the resistor and the heater for the switch, or to the other end of the heater and simultaneously to any of a plurality of closely spaced intermediate points on the resistor, or-to the said common connection of the heating element, resistor, and heater for the switch, thereby to obtain fine adjustment of the heat of the heating element.

6. In a heating device, a heating element; a thermostatic switch controlling the circuit for theheating element; a selector switch having four stationary, consecutively arranged contacts and a triple arm fan blade, said blade being shaped to span any three consecutive stationary contacts, and the blade being mounted to engage either solely the first :contact of .the switch, or

the first two switch contacts, orthree. consecutive contacts; a resistor element connected between'the fourth and third stationary contacts 9. of the selector switch; a second resistor element connected between the third and second stationary contacts of the selector switch; a heater for the thermostatic switch, connected between the first and fourth contacts of the selector switch; and current supply means connected with the fan blade and with one end of the heating element, the other end of the ement being eonnected with the said first contact of the selector switch,

7. In a heating device, a heating element; thermostatic switch controlling the circuit of the heating element; a heater for the thermostatic switch; a continuously variable resistor having two terminals, and having an open-circuit position, said heating element and heater having ends connected to one terminal of the resistor, and the other end of the heater being connected to the other terminal of the resistor; and means including a switching mechanism for connecting one leg of a current supply with the said other terminal of the variable resistor, the other leg of the current supply being connected to the other end of the said heating element.

8. In a heating device, a heating element; a thermostatic switch controlling the circuit of the heating element; a heater for the thermostatic svitch; a continuously variable resistor having a resistance element, a contact movable between limits and in opposite directions over the said element, said contact adjacent one limit of its movement being separable from the element, and the said resistor having a current-conducting bar engaged by the contact during its movement, the said contact, when moved to the said one limit and subsequent to its separation from the resistance element, separating from the bar; means connecting the current-conducting bar with one end of the heater for the thermostat, the other end of the heater and one end of the heating element being connected to one end of the resistance element of the esistor; and a pair of current supply wires, connected respectively to the other end of the heating element and to the contact of the said variable resistor.

9. In a heating device, a heating element; a thermostatic switch controlling the circuit for the heating element; a selector switch having three stationary contacts and a fan blade, said blade selectively spanning either pair or" adjacent contacts or connecting to one of the outside contacts of the switch; a heater for the ti e mostatic switch, connected across the outside contacts of the selector switch; a resistor connected between the center contact and the other of the outside contacts of the selector switch; and current supply means connected with the fan blade with one end of the heating element, the other end of the element being electrically connected with the said one outside contact of the selector switch.

10. In a heating device, a heating element; a ti mostatic switch controlling the circuit of the hELillllg element; a heater for the thermostatic ch; a resistor, said heating element, heater resistor having ends electrically connected with each other, constituting common connecn, and said therm static switch b g nected beta common connection; -ans for connecting leg or" a cut supply l ith the other end of the heating element; and means for selectively connecting the other leg of the current supply either solely to the other end of the heater for the switch, or to the other ends of both the resistor 10 and the heater for the switch, or to the 'said common connection of the heating element, resistor, and heater for the switch.

11. In a heating device, a heating element; a thermostatic switch controlling the circuit for the heating element; a selector switch having three stationary contacts and a fan blade, said blade selectively spanning either pair of adjacent contacts or connecting to one of the outside contacts of the switch; a heater for the thermostatic switch, connected across the outside contacts of the selector switch; a resistor connected between the center contact and the other'of the outside contacts of the selector switch; and current supply means connected with the fan blade and with one end of the heating element, the other end of the element being connected through the said thermostatic switch to the said one outside contact of the selector switch.

12. A heating pad comprising a heating element; a jacket enclosing and supporting the element; a thermostatic switch located in the said jacket, controlling the circuit for the'heating element; an electric supply cord leading from the jacket; a selector switch connected in the supply cord at a point removed from the jacket, said switch having three stationary contacts and a fan blade which latter'selectively spans either pair of adjacent contacts or connects to a predetermined one of the outside contacts of the switch; a heater for the thermostatic switch, located adjacent the latter and connected through the said supply cord across the outside contacts of the selector switch; a resistor located within the selector switch and connected between the center contact and the other of the outside contacts thereof; and current supply wires in the supply cord, connected respectively with the fan blade and with one end of the heating element, the other end of the element being electrically connected with the said one outside contact of the selector switch.

13. A heating pad comprising a heating element; a jacket enclosing and supporting the element; a thermostatic switch located in the said jacket, controlling the circuit for the heating element; an electric supply cord leading from the jacket; a selector switch connected in the supply cord at a point removed from the jacket, said switch having three stationary contacts and a fan blade which latter selectively spans either pair of adjacent contacts or connects to a predetermined one of the outside contacts of the switch; a heater for the thermostatic switch, located adjacent the latter and connected through the said supp y cord across the outside contacts of the selector switch; a resistor located within the selector switch and connected between the center contact and the other of the ouside contacts thereof; and current supply wires in the supply cord, connected respectively with the fan blade and with one end of the heating element, the other end of the element being connected through the said thermostatic switch to the said one outside contact of the selector switch.

14-. A heating pad comprising electric heating means; a jacket enclosing and supporting the heating means; a thermostatic switch located in said jacket, controlling the circuit of the heating means; a heater for the thermostatic switch located adjacent the latter; an electric supply cord leading from the jacket; a resistor located exteriorly of the jacket, said resistor at one point having a common electrical connection with one point of the heater through the said supply cord, said 151 A1 heating pad. comprising; a heating; ale

m'ent a l acket enclosing. and. supporting; the elee ment; 2, thermostatic switch;locateddnthesaid. jacket, controlling the circuit of the heating elementp a heater for the-thermostatic switch'glo catedladj'acent the latter; anEeJectricsuppIy cord: leadingiromithe jacket; a resistor. located exte.-- riorly of. theiackettv one encleachof. saidheating,

element and heater being. electrically connected 9* with each other, and.being; electrically connected throughthe:v supply cord-to: one end ofitheresiston to constitute acommon:- electricalconnection; a;

current-supply:wireein:the supply cord, connected Withith other end-ofthe heatin element;,a secondcurrent. supply Wire in the supply cord; and

manually;- operable switch means:located in the supply,- cord at a point removed from the jacket; said switch means including abridging contact for selectively connecting the second current supplywire: eith'er. solely to the other end of the heater-tor the. thermostatic switch, or tothe other ends ofboth the resistor and the heater for the switch, .0r' tov'thesaid common electrical. connection of, the heating element,v resistor, andv heater for. the swltch, theusaid resistor being mounted.

within. thesaid manually operable switch means.

JOSEPH YOUHOUSE.

REFERENCES CITED The following; references are of record in the file of thispatent:v

UNITED STATES PATENTS Name Date Taylor Apr. 8, 1941 FOREIGN PATENTS Country Date Germany Aug. :54, 15-27 Number i Number