US2430887A - Thermocouple for pilot burners - Google Patents

Description

Nov. 18, 1947. w. A. RAY

THERMO COUPLE FOR PILOT BURNERS Filed Sept. 25. 1943 INVENTOR FV/W/m A./?

ATTORNEY Patented Nov. 18, 1947 THERMOCOUPLE FOR PILOT BURNERS William A. Ray, Glendale, Calif., assignor to General Controls 00., a corporation Application September '25, 1943, "serial No. 503,791

4 Claims.

This invention relates to thermocouples, and, more particularly, to thermocouples adapted to generate electrical ener y for a controlling function.

Such thermocouples are formed by joining two dissimilar conductors. Heating of this junction to a temperature above the junctions formed at the other ends of the conductors generates a potential difference. The potential difference depends upon the difierence in temperature between the hot junction and the'cold junctions, which latter are usually formed by joining copper conductors to the ends of the thermo-electric conductors, all as is well understood.

It is one of the objects of this invention to improve in general thermocouples of this character.

It is still another object of this invention to provide a compact, simple thermocouple that is capable of generating suificient electrical energy to energize effectively an electromagneticall operated valve.

Thermocouples of this character are often used in fuel control systems, such, for example, as is illustrated in an application filed on February 4, 1941, in the name of William A. Ray, under Se al. Number 37 ,2 and entitled: Reset valve and control therefor," now Patent No. 2,403,611, dated July 9, 1946. The present application is a continuation in part of the said prior application.

In such fuel control systems, a burner is used to heat the hot junction. Accordingly, when the burner flame is extinguished, the generation of electrical energy ceases; and an electromagnet which normally holds the valve closure open is de-energized. This causes the valve to close. Usually, the pilot burner flame, rather than the main burner flame, is used for heating the hot junction.

It is another object of this invention to provide a thermocouple which can be effectively heated by an ordinary. gas pilot flame, and arranged so that a high temperature difierence between the hot and cold junctions is attained, although the thermocouple structure is compact. To provide this large temperature difference, care is taken to shield the cold junctions from the flame and from the heat of the furnace. Thus, short conductors can be used without seriously reducing the energ generated. Since some of the thermo-electric conductors in common use today (such as Chromel and Copel) are quite ex pensive, this economy in the use of materials is important.

This invention possesses many other advantages, and has other objects which may be made more easily apparent from a consideration of several embodiments of the invention. For this purpose, there are shown a few forms in the drawings accompanying and forming part of the present specification. These forms will now be described in detail, illustrating the general principles of the invention; but it is to be understood that this detailed description is not to be taken in a limiting sense, since the scope of the invention is best defined by the appended claims.

Referring to the drawings:

Figure 1 is an enlarged view, mainly in section, of a thermocouple structure incorporating the invention and shown as mounted on a pilot burner bracket and heated by the flame of the pilot burner;

Fig. 2 is an enlarged sectional view of a modified form of the thermocouple, shown as heated by a pilot burner flame;

Fig. 3 is a fragmentary sectional view, taken along plane 3-3 of Fig. 2; and

Fig. 4 is a sectional view of a further modification of the thermocouple structure.

In the form of the invention illustrated in Fig.

l, a pilot burner tube l is shown as supported on a bracket 2. This bracket may be carried by the main burner. Pilot burner I may be provided with a number of fuel jets 3, which, when ignited, form an annular flame 4. Fuel is fed to the burner I through a conduit 5.

The thermocouple structure is formed by a pair of thermoelectrically dissimilar conductors 6 and 1, shown as arranged closel side by side. Conductor 6 may be of Chromel and conductor 1 may be of Copel. The upper ends of these conductors 6 and l are joined by fused metal 8, thereby forming a hot junction. Insulation between the conductors 6 and l is provided by a thin layer of vitreous enamel 1 that covers one of the conductors, such as at Copel conductor 1.

A heat resistant sheath 9 encloses the conductors 6 and 1, as well as the hot junction 8. This sheath 9 may be made from stainless steel. It is shown as closely encircling the conductors 6 and I and as provided With a closed end In forming a thick wall. This end In is adapted to be directly inserted in the pilot flame 4. Heat is thus trans mitted through the wall of the sheath 9 to the hot junction 8, which is in good heat transmitting relation to the sheath.

The Chromel conductor 6 which has a much higher resistance than Copel, is made relatively short, terminating at acold junction II beyond the sheath 9. The Copel conductor I, having'less resistance than Chromel, may extend directly to one terminal of a load I2. The other terminal of the load I2 may be connected by copper lead I3 to the Chromel conductor 6 at the cold junction I I. The conductor I3 may also be bare, since the thin layer of enamel I on the Copel conductor I serves adequately to prevent short-circuiting between the conductors. The lead I3 and the conductor 6 are grounded on sheath 9.

The sheath 9 is attached, as by brazing, to a copper sleeve I4 which forms a continuation of the shield. This copper sleeve may be extended entirely through the bracket 2 and is fastened into the bracket 2 in a manner to be hereinafter W described. The sleeve I4 may extend substantially to the load I2, forming a conformable conduit for the conductors I and I3.

The bracket 2 is provided with an aperture I5 through which the sleeve I4 extends and in which it is snugly fitted. The lower portion of the aperture I5 is enlarged and threaded for the reception of a threaded sleeve I6 closely fitting over the tube I4. A collar H of deformable material, tapering from the center toward each end, is disposed in the space between sleeve I6 and the shoulder formed by the bottom of the enlarged lower portion of the aperture I5. This shoulder, as well as the aperture in sleeve I6, is slightly countersunk to receive respectively the corresponding ends of collar I'I. After the sleeve I6 is screwed in against collar II, the ends of the collar are compressed inwardly against tube I4, securely holding it in place.

Since Copel has a resistance not so great as that of Chromel, there is no intolerable power loss through conductor I which extends from the hot junction 8 to the load I2; and this isespecially true if the load I2, such as an electromagnet for operating a gas valve, is placed quite close to the furnace or burner.

The small mass of the conductors forming the thermocouple structure ensures that there is only a slight delay, after the pilot flame 4 is extinguished, in equalizing the temperatures at the hot and cold junctions. The generation of power is then stopped, resulting in rapid decay of energy supplied to the load I2. If this load is an electromagnet associated with a safety valve, as in the prior application hereinabove referred to, the closing of the safety valve follows very promptly upon failure of flame 4.

The generation of power by the thermocouple shown in Fig. 1 is quite large, since there is a large temperature difference between the cold junction II and the hot junction 8. This cold junction II is quite well shielded from the heat of the furnace in which the pilot burner I may be located. In this connection it is to be noted that, adjacent the cold junction II, the conductor 6 and the lead I3 are spaced from the wall of sleeve I4. The intervening air space forms an effective barrier against transmission of heat to the junction II.

In the form of the invention illustrated in Figs. 2 and 3, there is a hot junction I8 between the Copel conductor I9 and the Chromel conductor 20. The ends of these conductors are shown, in this instance, as extending through the upper wall of a cup-like member 2I of heat resistant material, such as stainless steel. Where these ends project through the member 2I, they are fused together to form the hot junction I8. The upper wall 23 of member 2| i purposely made convex, the more readily to accommodate the junction I8.

As before, the Copel conductor I9 extends to one terminal of the load. It is shown as extending into the flexible conduit 22 that is supported on the thermocouple structure in a manner to be hereinafter described. 1

A heat-resistant sheath 24 encloses the hot junction I8, as well as the member 2I. This sheath may be made from stainless steel. It is shown as in good thermal conducting relationship to the member 2 I, which is in tight frictional engagement with the sheath. The end wall 25 of the sheath 24 is shown as slightly thickened, and arranged to be directly inserted in the flame 26 of a pilot burner 21.

The Chromel conductor 20 is'quite short. It is joined to a copper lead 28 to form a cold junction 29. This copper lead 28 extends into the flexible conduit 22 where it is suitably insulated from the Copel conductor I9.

The conductors I9 and 20 are also appropriately insulated within'the sheath 24, as by the aid of a ceramic insulator 30. The insulator 30 is apertured to accommodate the conductors I9 and 20. It may be moved upwardly along these conductors to a point where there occur slight bends therein, to direct them through the apertures in wall 23.

A spacer tube 3| of metal is inserted within the sheath 24. Its upper end abuts the lower surface of the insulator 30. The cold junction 29 is located within the spacer 3|. As before, an air space surrounds the cold junction, and forms a barrier against transmission of heat thereto.

Abutting the lower end of the spacer 3I there is an insulator and spacer 32 which may be made from glass. This insulator 32 is provided with apertures for the passage of the lead 28 and the Copel conductor I9. It is also provided with a reduced portion over which telescopes a metal sleeve 34. This sleeve 34 extends beyond the bottom of the sheath 24. The sheath and the spacer 34 may be brazed or soldered together, as indicated at 35. Furthermore, the lower end of the spacer 34 may be brazed or soldered, as indicated at 36, to the flexible conduit 22. Lead 28 may be pinched, as shown at 31, to provide a stop for the conductor assembly.

The sheath 24 and member 2I co-operate to shield the conductors I9 and 20 from the flame 26. This is especially useful for the conductor I9, which is made from Copel, and which is less resistant to heat than Chromel. In assembling this form of the thermocouple, the sleeve 34 may be first joined to the flexible conduit 22; insulator 32 may be put in place over the conductors 28 and 29; the pinched parts 3'! on conductor 28 may be formed; the joint 29 is made. the spacer 3| and insulator 30 being then assembled; the conductors I9 and 20 are then bent to extend through the cup 2I, and the weld I8 is made. Lastly, the sheath 24 is telescoped over the entire structure.

In the form of the invention illustrated in Fig, 4, the Copel conductor 38 is shown as quite short, so that it extends substantially only to the lower end of the heat resistant cup-like member 2|. The Chromel conductor 39 and the Copel conductor 38 extend through the upper depressed wall 23 of member 2| and form, as before, the hot junction I8. Thus, for substantially the em tire length of the conductor 38 it is shielded both by sheath 24 and member 2|.

A cold junction 40 is formed between the end of the Copel conductor 38 and another Chromel conductor 4!. downwardly to the junction 42, where it is joined to the copper lead 43. The other Chromel conductor 39 likewise forms a junction 44 with another copper lead 45. These copper leads extend through the flexible conduit 22 to the load. The Chromel conductor 4| is much more resistant to heat than copper; yet its thermoelectric properties are quite similar to those of copper. Although the temperatures existing at the junction 40 are less than at the hot junction l8, nevertheless these temperatures may still be high enough to cause deterioration of copper. Substitution of the Chromel conductor 4i thus ensures against such deterioration.

Furthermore, the assembly includes the insulator 30, spacer 3|, and insulator 32, arranged substantially as before. The connections 42 and The Chromel conductor extends- 44 between the Chromel conductors and the leads V 43 and 45 are located within the spacer 3|, where an air space serves as a barrier against transmission of heat from the furnace.

The inventor claims:

1. In a thermocouple structure, a pair of thermocouple conductors of dissimilar material, a heat-resistant metal member to which an end of each of said conductors is attached, said ends being joined to form a hot junction, said member having a shielding portion surrounding the conductors and spaced therefrom, the space between the shielding portion and the conductors operating as a heat insulator, and a heat-resistant sheath enclosing the hot junction and contacting the member, and extending beyond the other end of at least one of the conductors.

2. In a thermocouple structure, a pair of thermocouple conductors of dissimilar material, a

, heat-resistant cup-like member to which an end of each of said conductors is attached, said ends being joined to form a hot junction, the annular portion of the member forming a shield surrounding the conductors and spaced therefrom, the space between the shield and the conductors operating as a heat insulator, and a heat-resistant sheath enclosing and contacting the cup-like member and enclosing the conductors, the end of the sheath being closed and in close heat transmitting relation to the hot junction.

3. In a thermocouple structure, a pair of thermocouple conductors of dissimilar material, a cup-like member having an end wall to which an end of each conductor is joined to form a hot junction, the annular portion of the member forming a shield surrounding the conductors and spaced therefrom, the space between the shield and the conductors operating as a heat insulator, one only of said conductors being of such length as to be substantially entirely shielded by said member, leads connecting to said conductors to form cold junctions, and a heat-resistant sheath enclosing and contacting the cup-like member, and enclosing the hot junction, the sheath extending substantially beyond said one of said conductors.

4. In a thermocouple structure, a pair of thermocouple conductors of dissimilar material, a cup-like member having an end wall to which an end of each conductor is joined to form a hot junction, the annular portion of the member forming a shield surrounding the conductors and spaced therefrom, the space between the shield and the conductors operating as a heat insulator, one only of said conductors being of such length as to be substantially entirely shielded by said member, a heat-resistant conductor joined to said one of said conductors to form a cold junction, leads connected to said heat-resistant conductor and to the other of said thermo-electric conductors, and a heat-resistant sheath enclosing and contacting the cup-like member, and enclosing the hot junction, the sheath extending substantially beyond the said one of said conductors.

WILLIAM A. RAY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS

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