US2902221A - Burner control system - Google Patents

Description

United States Patent BURNER CONTROL SYSTEM Charles E. Hajny, Milwaukee, Wis., assignor, by mesne assignments, to Minnesota Mining and Manufacturing Company, St. Paul, Minn., a corporation of Delaware Application June 22, 1956, Serial No. 593,242

12 Claims. (Cl. 236-9) This invention relates, in general, to control systems, and the embodiment selected for illustration has particular relation to burner control systems of the type in which an electric circuit for an electroresponsive valve in the fuel supply line to a main burner is under the control of a theromelectric generator subject to the heat of burning fuel at a pilot burner.

It is a general object of the present invention to provide an improved control system wherein a thermoelectric generator subject to the heat of the flame of a pilot burner affords the energizing current for the filament of an electron tube to directly control the fiow of current through said tube and thereby the energization of an electroresponsive valve in circuit therewith.

Another object of the invention is to provide an improved control system of the class described wherein the electrical energy for energization of the electroresponsive valve is of relatively high voltage as compared with the current supplied to the filament of the electron tube by the thermoelectric generator. Thus, the electron tube affords contactless means for directly controlling a relatively high voltage circuit by a relatively minute voltage thermoelectric circuit.

A more specific object of the invention is to provide an improved control system of the aforementioned character wherein the thermoelectric generator has at least one semi-metallic element.

Another object of the invention is toprovide an improved control system of the class described having a thermostat for cycling the electroresponsive valve, said thermostat being interposed in the thermoelectric circuit as distinguished from the higher voltage circuit, wherefore high voltage insulation and conduits are unnecessary in connection with the leads for said thermostat.

Another object of the invention is to provide an improved control system of the aforementioned character wherein the electroresponsive valve is opened and held opened by the flow of relatively high voltage electrical energy through the electron tube when the pilot burner is ignited, extinguishment of the pilot flame effecting deenergization of the filament of said tube and cut-off of the flow of said high voltage electrical energy through said tube to thus deenergize the electroresponsive valve which thereupon operates to shut off the supply of fuel to the main burner.

Further objects and advantages of the invention will become apparent as the description proceeds, a reference being had to the drawing accompanying and forming a part of this specification in which:

Figure l is a semi-diagrammatic View of the improved control apparatus utilized for the control of the flow of fuel to a gaseous fuel burner;

Figure 2 is an enlarged axial sectional view of the thermoelectric generator preferred for use in the improved apparatus; and

Figure -3 is a diagrammatic view of the magnetic structure of the illustrated electroresponsive valve shown in Figure 1.

Referring more particularly to Figure 1 of the drawing, the illustrated fuel control system comprises an electroresponsive valve 5 interposed in the fuel supply line 6 for a main fluid fuel burner 7 having a pilot or ignition burner S in coacting relation therewith. The valve 5 comprises body parts 9 and 10, the latter having inlet and outlet connections 11 and 12 respectively and having an annular valve seat 13 at said outlet connection. The body parts 9 and 10 provide a chamber 14, and disposed within said chamber is a valve member 15 cooperable with the valve seat 13 and carried by a pivotal arm 16. A tension spring 17, acting through the arm 16, biases the valve member 15 toward the seat 13.

The electroresponsive valve 5 may take a variety of forms, the illustrated valve including a transformer type electromagnetic operator for the valve member 15, said operator comprising a rectangular core 18 shown diagrammatically in Figure 3 and formed with a pair of oppositely disposed spaced pole pieces 19 and 20 having arcuate pole faces for cooperation with a magnetic rotor 21. The rotor 21 is fixed to a rotatable shaft 22 having a crank portion within the chamber 14 terminating in an eccentric pin 23. The pivotal valve arm 16 has a reversely bent upper end portion 24 engageable with the eccentric pin 23, and the bias of the spring 17, acting through the arm 16 and pin 23, biases the rotor 21 to the solid line position thereof shown in Figure 3. A primary winding 25 and a center tapped reduced voltage secondary winding 26 are Wound on opposite end legs of the core 18 as shown in Figures 1 and 3, said primary winding being adapted to be connected to a source of alternating line current 27 as shown.

The improved control apparatus includes means for controlling the flow of current through the secondary winding 26 and thereby the actuation of the valve member 15 responsive to a plurality of conditions. An electron tube 28 is provided with anode means which may comprise plates 29 and 30 and cathode means which may take the form of an indirectly heated cathode 31. The tube 28 may also have a filament 32 which, when energized, aifords heat for the cathode means 31. One end of the secondary winding 26 is connected in circuit with the plate '29, as by a conductor 33, and the other end of said winding is connected in circuit with the plate 30, as by a conductor 34. The center tap of the winding 26 is connected in circuit with the cathode means 31, as by a conductor 35 which may have a normally closed contact high temperature limit switch 36 interposed there in. Where the improved control apparatus is used for domestic central heating systems or the like, the high limit switch 36 may, for example, be located in the bonnet of the furnace.

The improved control apparatus includes novel means for energizing the filament 32 of the electron tube 28 and for thereby controlling the flow of current through said tube and hence through the secondary winding 26. The aforementioned energizing means comprises a thermoelectric generator 37 which may have a concentric type lead 38, the grounded outer tubular conductor 39 of which is connected to one terminal of the filament 32, and the insulated inner conductor 40 of which is connected in circuit with the other terminal of the filament 32. Interposed in the conductor 40 is a room thermostat 41 preferably comprising low resistance cooperating co-ntacts 42 and 43 encapsulated within an hermetically sealed expansible and contractible bellows 44 containing a temperature responsive expansible and contractible volatile fluid fill of the type which does not deleteriously efiect the resistance of the contacts 42 and 43. The contacts 42 and 43 are relatively movable to circuit making and circuit interrupting positions with contraction and expansion of the bellows 44.

Referring now to Figure 2 of the drawing, the thermoelectric generator 37 illustrated therein comprises a pair of thermocouple element means 48 and 49, the latter of which takes the form of an elongated generally cupshaped sheath member, preferably of stainless steel. The sheath 49 has a tubular sleeve portion 50 and a tip portion 51 which may serve as a heat probe means for the assembly. The opposite end of the member 4% is telescopically received within a counterbore formed within one end of an extension tube 52 of brass or other suitable material and is sealingly fixed therein, as by silver soldering or brazing at 67. The other end of the extension tube 52 is formed with a portion of reduced diameter to snugly receive one end of the coaxial lead 38, said sleeve also having an end recess adjacent the lead 38 in which said tube and lead are sealingly and electrically connected, for example by silver soldering or brazing, at 56.

The thermocouple element means 48 preferably cornprises a rod-like or cylindrical ingot or semi-metallic alloy or composition disposed in coaxial spaced relation within the sheath 49. Because the thermocouple element means 48 is of frangible material, the generator 35 is constructed in a manner to provide shock resistant mounting means therefor. The element means 48 includes an iron contact electrode 57 having a stem portion 58 formed with a shoulder 59. The tube 52 is formed with an internal annular shoulder 60, and surrounding the contact electrode stem portion 58 is an insulating washer 61 engaging the shoulder 60. Interposed between the insulating washer 61 and the stern shoulder 59 is a compression spring 62 which may take the form of a concavo-convex centrally apertured resilient disc also surrounding the electrode stem 58.

The sheath 49 is formed with a conical inner end wall surface 63, and the semi-metallic element 48 is formed with a complementary conical end wall surface 64 which is seated against the end Wall surface 63. The spring 62 exerts compressive stresses on the element 48, which stresses substantially reduce the net tensile stresses to which said element is subjected during transverse acceleration or shock, said compressive stresses not being so high as to exceed the compressive strength of said element. The bias of the spring 62 also provides the pressure necessary for a satisfactory pressure contact between the element 48 and the sheath 49 at the surfaces 63 and 64. The pressure type contact is not deleteriously effected by deformation of the element 48, for example on bending under transverse shock, and the conical nature of the surfaces 63 and 64 tends to maintain the biased element 48 in centered relationship within the tubular portion 50 of the member 49. The compressive stress under which the member 48 is placed increases the magnitude of deformation which said element can withstand without fracture and affords the generator 35 substantial shock resistance.

A tube 65 of insulating material preferably surrounds the contact electrode stem 58, and a flexible conductor 66 extends within the tube 65 and aifords an electrical connection between the stem 58 and the inner conductor 55 of the coaxial lead '63.

The thermocouple element 48 may, for example, be formed of a semi-metallic alloy or composition which may be characterized as a binary metallic compound of slightly imperfect composition, i.e. containing beneficial impurities constituting departures from perfect stoichiometry by reason of an excess of one of the metals over the other, and/or containing added beneficial impurity substances hereinafter referred to as promoters. Such semi-metallic compositions have semi-conductor like conductance, both electrical and thermal, and include mixtures of such binary metallic compounds, which may be denominated ternary metallic alloys or compositions. Certain of these alloys or compositions exhibit negative and certain exhibit positive electrical characteristics.

More specifically, the thermocouple element 48 may, for example, be formed of an alloy further described in the copending application of Sebastian Karrer, Serial No. 475,540, filed December 15, 1954, now Patent No. 2,811,- 570 and assigned to the assignee of the present invention, said alloy comprising lead and at least one member of the group telluriurn, selenium and sulphur. For example, a thermoelectric element 48 of lead-selenium-telluriurn composition could include a tellurium-selenium constituent in which the selenium is but a trace. In this case such constituent should constitute from 35% to 38.05% by weight of the composition, the balance (61.95% to 65% by weight) being lead. At the other extreme, where the tellurium-selenium constituent consists almost entirely of selenium with but a trace of tellurium, such constituent should comprise from 25% to 27.55% by weight of the final composition, the remainder (from 72.45% to 75% by weight) being lead. Between these two extremes, the selenium-tellurium constituent varies linearly with the ratio of selenium to tellurium (expressed in atomic percent) in the seleniurn-tellurium constituent.

The thermoelectric element 48 may also be formed of an alloy of lead, selenium and sulphur. For example, a thermoelectric element 48 of the lead-selenium-sulphur composition could consist of a selenium-sulphur constituent in which the sulphur is but a trace. In this case, such constituent should constitute from 25% to 27.55 by Weight of the composition, the balance (75 to 72.45% by weight) being lead. At the other extreme, where the selenium-sulphur constituent consists almost entirely of sulphur with but a trace of selenium, such constituent should comprise from 12.8% to 13.37% by weight of the final composition, the remainder (from 87.2% to 86.63% by weight) being lead. Between these two extremes the selenium-sulphur constituent varies linearly with the ratio of selenium to sulphur (expressed in atomic percent) in the selenium-sulphur constituent.

With regard to the aforementioned compositions, it Will be observed that in each case there is an excess of lead over and above the amount thereof necessary for satisfying the stoichiometric proportions of the compound formed in the second constituent or constituents, i.e. the tellurium, selenium or sulphur. For example, the composition consisting substantially of lead and selenium can contain up to 10.4% lead by weight of the total composition over and above the 72.41% by weight lead stoichiometrically necessary for combination with selenium.

The electrical characteristics of the aforementioned semi-metallic alloys, desirable, for example in thermoelectric elements, can be markedly and advantageously altered in a reproducible manner by the addition thereto of controlled amounts of matter other than the constituents of the base composition. Such additions may also be denominated beneficial impurities as distinguished from undesirable impurities. For convenience, these additions are hereinafter designated promoters, since they tend to enhance the electrical characteristics desired for the particular application of the base composition.

The aforedescribed base compositions exhibit negative thermoelectric power and negative conductivity. By the addition of certain promoters, such negative properties may be enhanced, while the polarity of the electrical properties of the base composition may be reversed by the addition of certain other promoters. The copending application of Robert W. Fritts and Sebastian Karrer, Serial No. 475,488, filed on December 15, 1954, now Patent No. 2,811,571 and assigned to the assignee of the present application, gives a complete description of the beneficial impurities, including both departures from perfect stoichiometry and promoters, which have been found to be effective for improvement of the electrical properties of semi-metallic thermoelectric generator elements when added to the aforementioned base compositions in minor amounts, for example up to a maximum of 6.9% by weight of beneficial impurity, including 3.9% excess lead and 3.0% promoter.

The proportions and ranges of the various constituents aforementioned and particularly the minimum limits of the lead constituent in the compositions, must be regarded as critical if the composition is to have the electrical and physical properties desired. If the lead content is significantly less than the minimum amount indicated for any particular selenium-tellurium or selenium-sulphur proportion, the polarity of the Seebeck changes and the desired electrical and mechanical properties will not be reproducible. On the other hand, if the lead content of any composition appreciably exceeds the aforementioned maximum limits, the resulting composition is too metallic in nature to afford satisfactory energy conversion elficiencies.

Not only are the proportions and ranges aforedescribed to be considered critical, but so also is the purity. More specifically, the limit of tolerable metallic impurity in non-promoted final compositions has been found to be on the order of 0.01%, and the composition must be substantially oxygen free, if the mechanical and electrical properties desired are to be obtained and are to be reproducible. In the case of promoted compositions, however, the limit of tolerable impurity is 0.001%.

In order to utilize any of the aforementioned base alloy or promoted compositions in electrical devices, for example as thermoelectric generator elements, they must necessarily be electrically contacted. As previously pointed out, electrical contact with the ingot 48 is made at one end with the inner wall surface 63 by means of a pressure contact. The electrical contact with the ingot at the opposite end, however, is made by bonding of the contact electrode 57 with the end surface of the ingot 48, and if desired, the aforementioned pressure contact can be replaced by such a bonded contact. in the latter case the element-electrode interface must have a mechanical strength at least comparable to that of the alloy of which the element 48 is made. The contact electrode must be chemically stable with respect to the element 48 and provides the necessary means for connecting said element into its electrical circuit while at the same time chemically isolating said element from the other conductors making up said circuit. Iron is especially adapted for use as contact electrode material for elements 48 of lead-tellurium-selenium composition, and pressure type contacts of carbon are suitable for elements 48 of any of the aforedescribed compositions including those comprising lead and sulphur.

Since, as is well known in the art, the electrical and thermal resistance of the thermoelectric generator 35 are dependent upon the configuration thereof as well as on the electrical and thermal conductivities of the elements 48 and 49, the relationship between the dimensions of each element can be obtained which afiords the highest thermal conversion efiiciency in such a mounting or assembly. In the embodiment described, the thermal conductivity of the semi-metallic element 48 is low as compared with that of the element 49 (for example .025 watt/cm./ C. as compared to .261 watt/cm] C.).

.For elements of any given thermal and electrical conductivities, the conversion eificiency depends strongly upon the ratio of thickness of the sheath 49 to the radius of the element 48, or more specifically, upon the crosssectional area of the tube. In the embodiment illustrated, this ratio of the radius of the element 4-8 to the thickness of the sheath 49 is preferably about 6 to l or more.

It is understood, of course, that the conversion efiiciency of the thermocouple is also dependent upon the difference between the hot and cold junction temperatures. For thermocouples utilizing a semi-metallic inner element having a low thermal conductivity, high temperature differences can be achieved by selecting for the semimetallic element a ratio of length to diameter, which in the exemplary embodiment herein disclosed is about 4 to 1, such that radiation transfer of heat from the surface of the inner element to the sheath establishes substantial temperature gradients within the inner element, particularly near the hot junction. When this is done, the heat flux into the inner element through the hot junction, i.e. the juncture of the faces 63 and 64, is exhausted to the case over the entire side wall surface of the inner element, allowing the inner cold junction, i.e. the juncture of the element 48 with the contact electrode 57, to assume a temperature only slightly greater than that of the outer cold junction, i.e. the juncture of the element 49 and sleeve 52. A further consequence of such radiative cooling is the reduced electrical resistance of the semi-metallic element 48, said element having a positive temperature coefficient of resistance. The radiation responsible for the removal of the heat transmitted across the hot junction takes place between the element 48, its cold junction electrode 57, and the metal walls of the element 49 and extension tube 52. Since the cold junction temperature under such circumstances is dependent upon the temperature of its environment, it is desirable to keep the ambient temperature low. The extension of the sheath to a cooler zone, as by the extension tube 16, provides a heat sink which aids in cooling the casing around the cold junctions.

The generator 37 is mounted, for example by a mounting bracket 41, with the heat probe portion 51 thereof subject to the heat of burning fuel at the pilot burner 8, so that whenever the pilot burner 8 is functioning properly, heat will be conducted to the hot junction aforementioned, and the generator 37 will supply sufiicient elec trical energy to energize the filament 32 of the electron tube 28. Energization of said filament, however, is under the control of the thermostat 41 in series circuit therewith, so that said filament is energized only when the thermostat 41 is calling for heat.

The operation of the improved control apparatus will now be described. With the parts of the apparatus in the position shown in Figure 1, the thermostat 41 is not calling for heat, and though the contacts 42 and 43 may be in engagement, the thermoelectric circuit is interrupted at said contacts so that the tube filament 32 is not energized even though the tip 51 of the generator 37 is heated at the time. With the filament 32 deenergized, the tube 28 does not conduct current and the secondary winding 26 of the electroresponsive valve 5 is effectively open circuited. When the thermostat 41 calls for heat, the contacts 42 and 43 move to circuit making position permitting thermoelectric current to flow from the generator 37 to the filament 32 to energize the latter. The heat afforded by the energized filament 32 heats the cathode 31 to permit a flow of electrons from the plates 29 and 30 to said cathode and thereby current flow in the circuit of the secondary winding 26.

Whenever the secondary winding 26 is open circuited, energization of the primary Winding 25 by alternating current from the line powered source 27 causes generation of flux by the primary winding, which flux flows through the core 18 and the portions thereof within the windings 25 and 26. When, however, a portion of the secondary winding 26 is closed circuited through the electron tube 28 by energization of the filament 32, reduced voltage alternating current is induced in said winding portion by the flux generated by the primary winding 25, and this induced current produces a field which opposes flux flow through that portion of the core within the secondary winding 26. As a result, the flux generated by the primary winding 25 is shunted from one of the pole pieces 19 and 20 to the other, across the intervening air gap and through the magnetic rotor 21, rotating the latter to the dot and dash line minimum air gap actuated position thereof shown in Figure 3. This rotation of the rotor 21, acting through the shaft 22, eccentric pin 23 and pivotal lever 16, opens the valve member 15 against the bias of spring 17 and permits fluid fuel to flow to the main burner 7 for ignition by the pilot burner 8.

In the illustrated valve 5, the halves of the secondary winding 26 on opposite sides of the center tap are energized alternatively, each being energized during one half of the alternating current cycle. For example, during one half of the alternating current cycle current may flow from the portion of the secondary winding 26 between the center tap and the conductor 34 through the conductor 34, from the plate 30 to the cathode 31, and back to the center tap through the conductor 35 and high limit switch 36. During the alternate half cycle current may flow through the portion of the secondary winding between the center tap and the conductor 33 through the conductor 33, from plate 29 to the cathode 31, and back to the center tap through the conductor 35 and high limit switch 36. The valve member 15 is held open as long as the thermostat 41 calls for heat and the hot junction of the generator 37 continues to be heated by the flame of the pilot burner 8. When the thermostat 41 no longer calls for heat, the energizing circuit for the filament 32 is interrupted at the contacts 42 and 43, and said filament and the cathode 31 thereupon cool to prevent further current flow from the plates 29 and 30 to the cathode 31, to thereby efi'ectively open circuit the secondary winding 26 and stop further shunting of flux between the pole pieces 19 and 20 to permit the rotor 21 to return to its solid line position of Figure 3 for closure of the valve member 15 under the bias of the spring 17.

The valve member 15 can thus be cycled between open and closed positions in accordance with the demands of the room thermostat 41 as long as the generator 37 is heated by the flame of the pilot burner 8. In the event that the high limit switch 36 becomes exposed to a predetermined extreme temperature, the circuit of the secondary winding 26 is interrupted by said switch so that no current can flow through any portion thereof so that the valve member 15 is moved to closed position if it is not already in said position. Further, in the event that the pilot burner 8 should become extinguished, the resultant cooling of the hot junction of the thermoelectric generator 37 prevents further energization of the filament 32 to effect closure of the valve member 15' and shut off of the fuel to the main burner 7.

The improved control apparatus by virtue of the use of the thermoelectric generator 37 to directly power the filament of the tube 28, afiords control means which is inexpensive and uncomplicated both in manufacture and operation. Moreover, by virtue of the location of the thermostat 41 in the thermoelectric circuit, the improved control apparatus avoids all of the problems presented by the use of high voltage thermostat leads. It will further be observed, that while the energization of the electroresponsive valve comes from the high voltage source 27, said valve is nevertheless under the control of instrumentalities located in the relatively minute voltage thermoelectric circuit.

The illustrated form of the invention has been selected for the purpose of disclosure only and is not intended to define the limits of the invention or to confine the latter to any particular use. Various changes and modifications may be made without departing from the spirit of the invention, for example the invention is not limited to the use of the specific electroresponsive valve or of the use of the specific electron tube 23 having an indirectly heated cathode, and all of such changes are contemplated as may come within the scope of the appended claims.

What is claimed as the invention is:

1. Control apparatus comprising a control circuit, an electron tube having anode and cathode means in said control circuit and filament means for heating said cathode means, a filament circuit independent of said control circuit including thermoelectric energy source means for energizing said filament means to permit a flow of electrons from said cathode to said anode means and hence a flow of electric current in said control circuit, and a thermostat in said filament circuit for controlling the energization of said filament means by said energy source means and thereby the current flow in said control circuit in accordance with the ambient temperature.

2. Control apparatus comprising a control circuit, an electron tube having anode and cathode means in said control circuit and filament means for heating said cathode means, a filament circuit independent of said control circuit including a thermoelectric generator having at least one semi-metallic element for energizing said filament means to permit a flow of electrons from said cathode to said anode means and hence a flow of electric current in said electric circuit, and a thermostat in said filament circuit for controlling the energization of said filament means by said generator and thereby the current flow in said control circuit in accordance with the ambient temperature.

3. Control apparatus comprising a control circuit, an electron tube having anode and cathode means in said control circuit and filament means for heating said cathode means, a cycling control device having a coil in said control circuit and having a control member biased toward one controlling position and movable toward another controlling position in response to current flow through said coil, a filament circuit independent of said control circuit and including a thermoelectric generator having at least one semi-metallic element for energizing said filament means to permit a flow of elec trons from said cathode to said anode means and hence a flow of electric current in said control circuit and coil for movement of said control member to said other position against said bias, and a cycling thermostat in said filament circuit for effecting energization and deenergization of said filament means by said generator and thereby cycling of said control member in accordance with fluctuations in the ambient temperature.

4. In combination, a cycling electroresponsive control device having a coil energizable from a source of relatively high voltage and having a control member biased toward a first position and movable against said bias toward a second controlling position in response to the flow of current through said coil, a burner, and contactless flame sensitive shut-off means comprising an electron tube having anode and cathode means in series circuit with said coil and including filament means for heating said cathode means, a filament circuit independent of said series circuit including a thermoelectric generator subject to the heat of burning fuel at said burner and having at least one semi-metallic element connected in circuit with said filament means for energizing the latter when said generator is heated to permit a flow of electrons from said cathode to said anode means and hence a flow of higher voltage electric current through said coil for disposition of said control member in said second position, and a thermostat in circuit with said filament means and generator for effecting energization and deenergization of said filament means and thereby cycling the said control member in accordance with fluctuations in the ambient temperature, outage of said burner and cooling of said generator effecting deenergization of said filament means and thereby shut oil of the current flow through said coil, whereupon said control member is returned to its said first position under said bias.

5. In combination, a cycling electroresponsive control device having a coil energizable from a source of relatively high voltage and having a control member biased toward a first position and movable against said bias toward a second controlling position in response to the flow of current through said coil, a burner, and contactless flame sensitive shut-01f means comprising an electron tube having anode and cathode means in series circuit with said coil and including filament means for heating said cathode means, a filament circuit independent of Said series circuit and including a thermoelectric generator subject to the heat of burning fuel at said burner and having at least one semi-metallic element connected in circuit with said filament means for energizing the latter when said generator is heated to permit a flow of electrons from said cathode to said anode means and hence a flow of higher voltage electric current through said coil for disposition of said control member in said second position, a thermostat in circuit with said filament means and generator for effecting energization and deenergization of said filament means and thereby cycling of said control member in accordance with fluctuations in ambient temperature, and a thermostatic high temperature limit switch having normally closed contacts in series circuit with said coil and operable in response to an extremely high temperature to prevent current flow through said coil and thereby eflect disposition of said control member in said first position, outage of said burner and cooling of said generator effecting deenergization of said filament means and thereby shut off of the current flow through said coil, whereupon said control member is returned, to its said first position under said bias.

6. Control apparatus comprising a control device having a center tapped coil adapted to have an alternating current impressed thereon and having a control member movable from one controlling position to another in response to current flow through a portion of said coil, an electron tube having at least two anodes and having cathode and filament means, said anodes being connected in circuit with opposite ends of said coil respectively, and said cathode means being connected in circuit with the center tap of said coil, and thermoelectric energy source means connected in circuit with said filament means for energizing the latter to permit flow of an impressed alternating current from said cathode means to said anodes alternatively and thereby through alternate halves of said coil during alternate halves of the alternating current cycle for disposition of said control member in said other position.

7. Control apparatus comprising a control device having a center tapped coil adapted to have an alternating current impressed thereon and having a control member movable from one controlling position to another in response to current flow through a portion of said coil, an electron tube having at least two anodes and having cathode and filament means, said anodes being connected in circuit with opposite ends of said coil respectively, and said cathode means being connected in crcuit with the center tap of said coil, thermoelectric energy source means connected in circuit with said filament means for energizing the latter to permit flow of an impressed alternating current from said cathode means to said anodes alternatively and thereby through alternate halves of said coil during alternate halves of the alternating current cycle for disposition of said control member in said other position, and condition responsive circuit controlling means in the circuit between said cathode means and center tap for controlling the current flow through said coil.

8. Control apparatus comprising a control device having a center tapped coil adapted to have an alternating current impressed thereon and having a control member movable from one controlling position to another in response to current flow through a portion of said coil, an electron tube having at least two anodes and having cathode and filament means, said anodes being connected in circuit with opposite ends of said coil respectively, and said cathode means being connected in circuit with the center tap of said coil, a thermoelectric generator having at least one semi-metallic element connected in circuit with said filament means for energizing the latter to permit flow of an impressed alternating current from said cathode means to said anodes alternatively and thereby through alternate halves of said coil during alternate halves of the alternating current cycle for disposition of said control member in said other position, and a condition responsive circuit controlling device in circuit with said filament means and generator for controlling energization of said filament means and thereby the current flow in said coil in accordance with the ambient condition.

9. Control apparatus comprising a control device having a coil provided with a lead wire intermediate its ends defining first and second coil portions between said lead wire and said ends, said coil being adapted to have an alternating current impressed thereon, said control device also having a control member having first and second controlling positions and movable from said first controlling position to said second controlling position in response to current fiow through either one of said coil portions, an electron tube having first and second anode means, cathode means and filament means for heating said cathode means, electric energy source means connected in circuit with said filament means for energizing the latter, and means affording electrical connection of said first and second anode means with the opposite ends of said coil respectively and said cathode means with said lead wire, whereby upon impression of an alternating current on said coil current flows through said coil portions alternately during alternate halves of the alternating current cycle for disposition of said control member in said second controlling position but only when said filament means is energized.

10. Control apparatus comprising a control device having a coil provided with a lead wire intermediate its ends defining first and second coil portions between said lead wire and said ends, said coil being adapted to have an alternating current impressed thereon, said control device also having a control member movable from one controlling position to another in response to current flow through one of said coil portions, an electron tube having first and second anode means, cathode means and filament means for heating said cathode means, electric energy source means connected in circuit with said filament means for energizing the latter, means afiording electrical connection of said first and second anode means with the opposite ends of said coil respectively and said cathode means with said lead wire, whereby upon impression of an alternating current on said coil current flows through said coil portions alternately during alternate halves of the alternating current cycle for disposition of said control member in said other position but only when said filament means is energized, and condition responsive circuit controlling means in the circuit between said cathode means and lead wire for controlling the current flow through said coil.

11. Control apparatus comprising a control device having a coil provided with a lead wire intermediate its ends defining first and second coil portions between said lead wire and said ends, said coil being adapted to have an alternating current impressed thereon, said control device also having a control member movable from one controlling position to another in response to current flow through one of said coil portions, an electron tube having first and second anode means, cathode means and filament means for heating said cathode means, electric energy source means connected in circuit with said filament means for energizing the latter, means afifording electrical connection of said first and second anode means with the opposite ends of said coil respectively and said cathode means with said lead wire, whereby upon impression of an alternating current on said coil current flows through said coil portions alternately during alternate halves of the alternating current cycle for disposition of said con trol member in said other position but only when said filament means is energized, and condition responsive circuit controlling means in circuit with said filament means and said source for controlling energization of said filament means and thereby the current flow through said coil.

12. Control apparatus comprising a control device having a coil provided with a lead Wire intermediate its ends defining first and second coil portions between said lead wire and said ends, said coil being adapted to have an alternating current impressed thereon, said control device also having a control member movable from one controlling position to another in response to current flow through one of said coil portions, an electron tube having first and second anode means, cathode means and filament means for heating said cathode means, electric energy source means connected in circuit with said filament means for energizing the latter, means affording electrical connection of said first and second anode means with the opposite ends of said coil respectively and said cathode means with said lead wire, whereby upon impression of an alternating current on said coil current flows through said coil portions alternately during alternate halves of the alternating current cycle for disposition of said control member in said other position but only when said filament means is energized, cycling first condition responsive circuit controlling means in circuit with said filament means and said source for controlling energization of said filament means and thereby current flow through said coil in response to normal fluctuations in 12 the ambient condition, and second condition responsive circuit controlling means in the circuit between said cathode means and lead wire for interrupting the current flow through said coil in response to an extreme in the ambient condition.

References Cited in the file of this patent UNITED STATES PATENTS 2,224,709 Uehling Dec. 10, 1940 2,280,353 Ray Apr. 21, 1942 2,281,619 Roberts May 5, 1942 2,373,788 Sivertsen Apr. 17, 1945 2,397,756 Schwarz Apr. 2, 1946 2,441,568 Finison May 18, 1948 2,444,568 Isserstedt July 6, 1948 2,465,036 Ray Mar. 22, 1949 2,610,677 Lange Sept. 16, 1952 2,635,637 Karrer Apr. 21, 1953 2,765,119 Marvin Oct. 2, 1956 2,767,923 Matthews Oct. 23, 1956 FOREIGN PATENTS 265,519 Great Britain Feb. 17, 1927

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