US1615451A - Thermocouple - Google Patents

Description

ian 25, 1927 r, R. HARRISON THERMOCOUPLE 2 Sheets-Sheet 1 Filed Feb. l, 1926 @4f/M@ ATTORNEY l Jan. 25, i927 T. R.- HARRISONV THERMOCOUPLE Filed Feb. l. 1926 -2 Sheets-Sheet 2 r1- w fr A MSM TW l@ Qwb xNb )VG INVENTOR Patented Jan. 25;, i927.

'rIIoMAs n. HARRISON, or PHILADELPHIA, PENNSYLVANIA, AssIGNoR 'ro THE BROWN INSTRUMENT COMPANY, OPPIIILADELPIIIA, PENNSYLVANIA, Acon- PORATIN 0F PENNSYLVANIA.

THEIuNocoUPLE.

Application mea February 1, 192e. seri'ai No. 85,176.

The general object of the present invention is to provide simple and effective means for protecting thermo-couples employed in measuring the high furnace temperatures from injurious contact with vthe furnace gases. Heretofore serious troubles have ,been experienced as a result ofthe der teriorating action of furnace gases on the l thermo-couple conductors both when the thermo-couple elements are the so-called noble metals employed in measuring high furnace temperatures as for example in burning refractories where' the thermo-couple may be exposed to furnace temperatures as high as 27 O0 F. or above, orare the base' metals employed in measuringtemperatures not higher than 180()o F. or thereabouts. In thermo-couples employed under such conditions the active portions of the thermo-cuple conductors, including the hot junction of the thermo-couple are commonlyT surrounded by a tube or casing of non-metallic material such as unglazed porcelain, fire clay, or analogous material, the purpose of such tube or casing being to prevent the furnace, gases from coming into contact with the thermo-couple conductors. In practice, however, when such a protective tube be- .conies highly heated in use, furnace gases frequently pass through the pores of, or through cracks in the. protective tube in amount suiiicient to corrode'and destroy or impair the effectiveness of the thermo couple.

In accordance' with the present invention, thermo-couples for measuring high furnace temperatures are protected against injurious contact with furnace gases in a simple and practically feasible manner, by maintainingv a minute ow of air through the interior of the protective casing of theI thermo-couple. This flow of air must be relatively minute' in quantity to prevent it fromhaving anyappreciable or significant cooling 'eifect which would make the thermo-couple indications A lower than vthey should be, but only a very minute flow 'of airl through the thermo-couple casing is required to eliminate the injurious consequences of' furnace gasj leak# age into the thermo-couple. casing. To secure the desired How of `air through the thermo-couple casing, I may employ the furnace` draft, as by providing an outlet connection from the thermo-couple casing to a portion of the furnace in which a minus pressure exists while at the same time provlding an in-` let to the casing for atmospheric air which is sucked through the casing by the furnace draft suction; In lieu of using the furnace draft suction in this manner, any other suitable and convenient aspiratlng means may be employed. For instance, 1n some cases I may provide a thermo-couple casing with a vertical outlet pipe extending upward from the thermo-couple casing along the outer wall of the furnace and open at its topto the atmosphere so that the heat of the furnace coupled with the heat absorbed by the thermo-couple 'casing will provide a stack action giving the-necessary draft.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and formingy a part of this application. For a better understanding of the invention,

however. its advantages and specific objects.

attained with its use, reference -should be had to the accompanying drawings and descriptivematter'in which I have illustrated and described preferred embodiments of my invention.

Of the drawings: Fig. 1 is a sectionalV elevation of la. portion of a furnaceand thermo-couple for measuri ing the temperature therein;

Fig. 2 is an enlarged section of the mo-couple shown in Fig. 1;

Figs. 3. 4, 5, and 6 2are views taken similarly to Fig. 2 each illustrating a different modification.

In the drawings and referring first to Figs. 1 4and 2, A represents the wall of a furnace. Into ahigh temperature portion which as shown in Figs. 1 and 2, comprises united at B to form a hot junction and conther- A of its interior extends a thermo-couple, l

nected at their .opposite .ends to the usual terminals provided'Y in the thermo-couple head C. The two elements B which are encased and separated bysuitable refractory insulating material D, -are surrounded by a porcelain or analogous tube E having its inner end closed and its outer end connected to` ed into a socket formed for the purpose in f Athe head C, and a cement packing F between the metal tube F and the casing E. The

outer end of the casing E is openA to a chamber C' in the head C sealed from the external atmosphere by the terminal support ing plate C2 except for a fine inlet port C8 through which atmospheric air may enter the chamber C and pass into the space within the casing E surrounding the insulated' 'elements B which do not fill the casing E.

nected by -a pipe G to the furnace chamber A as shown in Fig. 1, wherein a pressure yless than that of the atmosphere is assumed to exist. l

With the arrangement shown in Flg. 1, the furnace draft suction transmitted to the inner end of the casing E through the pipes G and G, draws atmospheric air into the chamber C in thethermo-couple head C through the port C3. and thence through the casing E to the inner end of the latter from which the air passes into theopeu inner'end of the tube G. The air flow thus set up through the casing tube E and out ot the latter through the tube G carries with it any furnace gas passing through the pores of, or cracks in the porcelain tube E, and only a relatively minute stream of air is required to prevent a furnace gas content in the atmosphere surrounding. the thermocouple elelnents B suliiciently large to make 4that atmosphere injurious to the thermocouplel elements. In particular', the flow of air required toprevent injurious contamination of the atmosphere surrounding the thermo-couple elements need and should not be large enough to have any significant cooling action on the hot junction B of the thermo-couple. The cross sectional areas ot' the passages, and particularly the bore of the'inlet passage C8 and of the pipes G or G should be made small enough relativel to the furnace draft suction so as to keep the air flow through the thermo-couple casing suitably small.

Various modifications of the apparatus shown in Figs. 1 and '2 may be made, and some'of these are shown by way of example 1n Flgs. 3, 4, 5, and 6. The arrangement shown in Fig. 3 differs from that shown i-n Fig. 1, merely in that the thermoscouple elements B and their insulation D are 4enclosed in a separate casing tube H having a closed vinner end and ordinarily formed ofv `Which may leak through the pores of, or cracks inthe tube H is not a furnace gas atmospherc, but an atmosphere of air admixed with a small portion only of the furnace,-

gases which may leak through the tube E.

The arrangement shown in Fig. 4 differs from that shown in Figsl, 2, and 3, in that the pipes G and G' are dispensed with, and in lieu thereof a small port E is formed in the inner end of the casing tube E, so that the furnace draft suction draws atmospheric air into the chamber C', and thence through the port C, tube E, and port E into the furnace chamber. As shown' in Fig. 4, thc casing H is centrallydisposed in the casing E and is supported at its outer end by a iiange or cross head part H.

The arrangement shown in Fig. 5 dill'ers from that shown in Fig. 4 in that atmospheric air entering the portion of the chamber C at the outer side of thc cross head or flange portion H through a port C10, is drawn through the member H to the inner end of the latter and thence through a port `H2 in the inner end of the casing member H. into the space between the casing member H and surrounding casing E, the air then passing bach through said space to the portion of the chamber Cat the inner side of the flange or cross head portion Il and escaping through the outlet pont C.l The voutlet port C may be connected to the interior ol the 'furnace chamber with which the thermo-couple is used by a pipe similar to the pipe G oliFigs., 1, 2, and 3, but as shown. the port C11 is connected to the lower. end of an uprising pipe G2 which is adapted to serre as a sort of a stack or chimney for producing the .desired flow 0f air through the thern'io-couple casing. The stack draft created by the pipe G2, may obviously beI augmented by locating the pipe G2 adjacent the hot outer Wall of the furnace with which the thermo-couple is used so as to thereby increase the temperature and decrease the density of the column of air in the pipe G2.

The arrangement shown in' Fig. 5v ossesses the advantage over the constructions previously referred to, in that an increase in furnace chamber gas pressure cannot cause the furnace gases to back up in the thermocouple 'casing through the pipe G2, as they may through the pipe G of Figs.v1, 2, and 3. or through the port E of Fig. 4.

' It will be understood, of course, that the thermo-couple casing and head may vary in form rfrom those illustrated in FigsQl to 5. For example, as shown in Fig. 6, the head CA may be provided with a support C21 for a bushing C22 which surrounds and supports the outer end of the inner thermo-couple casing H, and closes the outer end of the4 casing E. In Fig. 6 the terminal support C20 is formed With an aperture C23 to permit atmospheric air to. enter the outer end of the member H which is formed-at its inner end with a port H2 opening into the c surrounding space within the casin member Air is drawn out of the annu ar space 4between the ca'sing members E and4 H through a port C2* formedin the bushing C22 into the chamberCz5 in the head CA to which a pipev G vis connected as in the constructions shown in Figs. 1, 2, and 3. lt

will be understood further that while in suparatus disclosed without departing from the spirit of my invention as set forth lin the appended claimsand that in some cases certain features of my invention may be `used to advantage Without a corresponding use of other features.

-Having now described my invention what I claim as new and desire to secure'byLetf ters Patent is;

LA thermo-couple comprising thermocouple conductors and a casing receiving said conductors and provided with means .forming a path of -low for a stream of air adapted to sweep4 out noxious gases leaking "'ifnto said casing.

2. In a. thermo-couple for measuring high temperatures, the combination with thermocouple conductors united to form a hot ]unction. of an elongated casing formed a longitudinally extending chamber receiving said yconductors and having one closed end 4adjacent. which said hot junction is located,

and means providing an aircliannel within,

and extending longitudinally of said casing and communicating withV said chamber adjacent'its closed 'endg 3.A A thermo-couple comprising thermocouple conductors and an elongated casing receiving said 'conductors and provided with means forming a iow pathand'means for creating an air flow along said ath adapted to sweep out noxious gases lea 'ng through saidgases.

4. The combination with thermo-couple conductors united to form a hot'junction, of an elongated casing formed'with a longitudinally extending chamber in which said conductors are received and having one closed end adjacent which said hot junction is located, means providing an air channel within and extending longitudinally of said casing and in communication with said chamber adjacentaits closed end, and means for creating an air flow longitudinal of said casing in one direction through said chamber andin the oppositedirection through said channel.

5. The combination with a furnace, of a thermo-couple extending into the furnace and comprising thermo-couple conductors and a refractory protective casing forsaid conductors, and means for utilizing the furnace draft to create a small air flow through said casing to thereby protect said conductors against injury from furnace gases leak- 'ing through saidcasing. g

- Signed atV Philadelphia, in the countyof Philadelphia. and State of Pennsylvania,

this 29th day of January, A. D.l 1926.

THOMAS R. HARRISON.

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