Abstract:
A thermocouple sensing element comprising a first electrically conductive member formed of one of two dissimilar metals and a second electrically conductive member formed of the second of the two dissimilar metals attached to the first electrically conductive member, and located within the first electrically conductive member, the first electrically conductive member and the second electrically conductive member forming two elements which generate an electrical potential difference under varying conditions of heat.

Description:
CROSS REFERENCE TO RELATED PATENT APPLICATIONS 
     This application is related to and is a division of my co-pending application of the same title, Ser. No. 09/301,809 filed Apr. 28, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     I. FIELD OF THE INVENTION 
     This invention is in the general field of temperature control and indicating systems; 
     The invention is more particularly directed to thermocouples used for temperature control and indicating; 
     The invention is more directly in the field of thermocouples wherein an outer thermocouple shield is formed of one of the two dissimilar thermocouple metals In one of several variations of this invention I use two concentric cylindrical members, each made of one of the two dissimilar metals. This particular variation has some very interesting qualities since a great area is involved for each of the two dissimilar metals increasing the response of the potential created by the heat to which they are subjected in use resulting in a thermocouple system having faster response, greater accuracy, more reliability, and longer useful life than systems heretofore in use. In another variation I utilize a first thermocouple member of the first of the two thermocouple metals with successive coatings of various materials including one coating of the second of the two thermocouple materials. In all of the variations of this invention a basic innovative feature is the use of one of the thermocouple metals surrounding the other thermocouple metal with additional protective and enhancing features. 
     II. Description of the Prior Art 
     Thermocouples are well known and in wide use. There have been so many thermocouple systems devised that it would be futile to attempt to list them in detail. However, I do not know of any thermocouple where one of the two dissimilar thermocouple metals surrounds the other of the two dissimilar thermocouple metals to create the electrical potential difference to determine the temperature as I have done in this invention. I have provided other improvements as well which will be detailed below. 
     SUMMARY OF THE INVENTION 
     Thermocouples are widely used to sense temperatures, particularly high temperatures. Thermocouples generally operate by sensing an electrical potential generated between two connected wires of dissimilar materials when subjected to temperature variations. The electrical potential generated is then converted to an indication of actual temperature as is known to those skilled in the art. 
     A basic thermocouple normally consists of a hollow, bullet shaped metallic shield with two dissimilar metallic connected wires within the shield. A glass seal or the like seals around the open end of the shield and also seals around the wires. 
     The interior of the thermocouple is packed with insulation material. The insulation is necessary to prevent the two wires from shorting at a position other than their one connection at one end of each wire. However, the insulation is also a major problem. The insulation reduces the sensitivity of the instrument. Additionally, the seal will randomly crack on cooling. When this occurs, the result can be the introduction of moisture into the insulation. Moist insulation contaminates the wires and their connection to each other (referred to as “poisoned” by those skilled in the art) and reduces sensitivity and may short the two wires. 
     With my invention, there is no longer a need for insulation. I accomplish this by forming the shield from one of the two dissimilar metals used to make a thermocouple work. I then attach a wire formed of the second of the two dissimilar metals to the interior of the bullet shaped shield. There is no requirement for insulation, thus the poisoning and other problems caused by the insulation are eliminated. 
     Being constructed in this manner my new thermocouple may be filled with an inert gas, the interior may be vacuumed, the shield may be coated inside and/or outside, or the interior of the shield may even be left open to the atmosphere. The wire inside the shield may be stretched tight to provide maximum sensitivity and accuracy. 
     In one interesting variation of my invention I form a thermocouple of two dissimilar metallic concentric tubes. One of the tubes is formed of the first of two dissimilar metals and the second tube is formed of the second of the two dissimilar metals. This provides for a large and uniform surface of each metal resulting in interesting time, sensitivity, and magnitude of response when the tubes are subjected to heat. 
     In what is, perhaps, the most innovative, useful and unique variation of my basic premise for thermocouples, I commence by forming a wire or the like made of the first of two thermocouple dissimilar metals. I then coat the wire or the like with a layer of non electrical conducting material, leaving a segment of the wire or the like not coated Next, I coat the non electrical conducting material and the not coated segment of wire or the like with a layer of the second of the two thermocouple metals. Now, I may, but am not required to, coat the entire wire with its previously recited coatings with a layer of corrosion resistant material or the like. Finally, by using clamps or other means clear to those skilled in the art I make an electrical contact to each of the two dissimilar thermocouple materials. These last mentioned two contacts are for connection to measuring instruments or the like. 
     It is an object of this invention to provide a thermocouple without insulation in the thermocouple shield; 
     Another object of this invention is to provide such a thermocouple which will be more sensitive and more accurate than previously known thermocouples; 
     Another object of this invention is to provide a thermocouple with a longer useful life than prior thermocouples: 
     Another object of this invention is to provide compact and miniature thermocouples of high sensitivity, long life, and maximum reliability. 
     The foregoing and other objects and advantages of this invention will become apparent to those skilled in the art upon reading the description of preferred embodiments, which follows, in conjunction with a review of the appended drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic section of a thermocouple of the prior art; 
     FIG. 2 is a schematic section of a thermocouple suitable to practice the method of this invention; 
     FIG. 3 is an enlarged view of the area  3  on FIG. 2; 
     FIG. 4 is a schematic perspective of an alternate embodiment of this invention; 
     FIG. 5 is a section on  5 — 5  on FIG.  4 . 
     FIG. 6 is a schematic perspective of another alternate embodiment of this invention; 
     FIG. 7 is a section on  7 — 7  on FIG. 6; 
     FIG. 8 is an enlarged fragmentary section of the area  8  on FIG. 6; 
     FIG. 8 a  is an elevation of the area  8   a  on FIG. 8; and 
     FIG. 9 is a schematic perspective of another alternate embodiment of this invention. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     An inventory of the drawing items bearing numerals: 
     
       
         
               
               
             
           
               
                   
               
               
                 Item 
                 Description 
               
               
                   
               
             
             
               
                  10 
                 prior art thermocouple 
               
               
                  12 
                 shield 
               
               
                  14 
                 wire 
               
               
                  16 
                 wire 
               
               
                  18 
                 connection of wires 
               
               
                  19 
                 large end of sleeve 
               
               
                  20 
                 seal 
               
               
                  22 
                 insulation within thermocouple 
               
               
                 100 
                 thermocouple suitable to practice the method of this invention 
               
               
                 112 
                 shield 
               
               
                 114 
                 wire 
               
               
                 116 
                 wire 
               
               
                 117 
                 connection of wire to shield 
               
               
                 117a 
                 clamp 
               
               
                 118 
                 connection of wire to shield 
               
               
                 119 
                 large end of shield 
               
               
                 120 
                 seal 
               
               
                 122 
                 space within thermocouple 
               
               
                 123 
                 coating 
               
               
                 124 
                 coating 
               
               
                 200 
                 thermocouple formed of two concentric cylinders 
               
               
                 212 
                 outer cylinder 
               
               
                 212a 
                 wire 
               
               
                 214 
                 inner cylinder 
               
               
                 214a 
                 wire 
               
               
                 218 
                 connector between cylinders 
               
               
                 230 
                 insulated spacers between cylinders 
               
               
                 232 
                 base support elements 
               
               
                 300 
                 alternate cylindrical thermocouple 
               
               
                 312 
                 double wall cylinder 
               
               
                 312a 
                 outer cylinder of double wall cylinder 
               
               
                 312b 
                 closed end of double wall cylinder 
               
               
                 312c 
                 inner cylinder of double wall cylinder 
               
               
                 312d 
                 wire lead of double wall cylinder 
               
               
                 314 
                 single cylinder within double wall cylinder 
               
               
                 314a 
                 pointed contact element on the end of cylinder 314 
               
               
                 314b 
                 contact of 314a and 312b 
               
               
                 314d 
                 wire lead of single cylinder 314 
               
               
                 400 
                 alternate thermocouple of this invention 
               
               
                 412 
                 element formed of first of two thermocouple metals 
               
               
                 414 
                 coating of second of two thermocouple metals 
               
               
                 416 
                 where element 412 and coating 414 are in contact 
               
               
                 418 
                 lead wire 
               
               
                 418a 
                 connection of 414 and 418 
               
               
                 419 
                 lead wire 
               
               
                 419a 
                 connection of 412 and 419 
               
               
                 420 
                 non electrical conductive coating 
               
               
                 422 
                 protective coating 
               
               
                   
               
             
          
         
       
     
     Those skilled in the art will be well aware of the heretofore known construction and operation of thermocouples. The following description is not intended to be a complete description of the operation of thermocouples, but only a sufficient mention of the features to enable those interested to understand and practice my new invention. 
     FIG. 1 illustrates the construction of a basic thermocouple of the art prior to my present invention. The thermocouple normally consists of a hollow, bullet shaped, metallic (stainless steel or the like) shield  12  with two dissimilar metallic wires  14  and  16  connected at  18 . A seal  20  of glass or the like seals around the end  19  of the shield and also seals around the wires  14  and  16 . The dissimilar wires  14  and  16  will be, for example, Chromel (nickel chromium alloy) and Alumel (a nickel alloy with aluminum, manganese, silicon and constantan {nickel copper alloy]). Insulation material  22  fills the interior of the shield. The insulation is necessary to prevent the wires  14  and  16  touching or otherwise electrically discharging to each other at positions other than their joinder at  18 . 
     There are many other thermocouples with added features, but the basic sensing arrangement is normally the same as that shown in FIG.  1 . 
     FIG. 2 is a view similar to FIG. 1 showing a basic thermocouple sensing apparatus utilizing the features of my present invention. The shield  112  is formed of one of the two dissimilar metals such as the metals described above. The wire  114  is formed of the other metal such as described above. The wire  114  is welded or otherwise attached to the shield at  118 . A lead wire  116  is welded or otherwise attached to the shield at  117 . Alternately, as shown in FIG. 3, the shield  112  could extend through the seal and wire  116  could be clamped to the shield by a clamp  117   a  as will be understood by those skilled in the art The two wires  114  and  116  will then lead to instrumentation to convert potential differences to temperature readings as is known to those skilled in the art. The wire  114  can be stretched by means known to those skilled in the art to prevent sagging when subjected to heat in order to further enhance accuracy in operation. In FIG. 2 the shield  112  is shown as having two coatings  123  and  124 . These coatings, or one of them, may be used or not. They may be plated, or otherwise applied, in a manner known to those skilled in the art to reduce the possibility of corrosion and contamination, to enhance heat transfer, to lower electrical resistance or one of many other purposes which may occur to those skilled in the art. 
     FIGS. 4 and 5 show another totally unique and valuable thermocouple using the basic premise of this invention. In this case the conductor shield  212  is in the form of a cylinder constructed of the first of the two dissimilar metals. The inner conductor cylinder  214  is made of the second of the two dissimilar metals. Lead wires  212   a  and  214   a  are attached at  212   b  and  214   b  to cylinders  212  and  214  respectively. The lead wires will go the instrumentation as is known to those skilled in the are. A series of insulator spacers  230 , or other means known to those skilled in the art will maintain the two cylinders separated from each other. A pair of insulator base supports  232  will support this embodiment of the thermocouple either directly within a furnace, kiln, or the like or within a thermowell associated with the device for which the temperature values are being detected or other means known to those skilled in the will be used to maintain the thermocouple sensing device in the desired position. 
     FIGS. 6,  7 ,  8 , and  8   a  show another version of the thermocouple with the two dissimilar metals in the shape of concentric cylinders  300 . 
     In this form, one cylinder  312  is a double cylinder formed of the first of two dissimilar thermocouple metals. Outer cylinder element  312   a  has a closed end at  312   b  with its other end being open. Inner cylinder  312   c  is formed integrally with end  312   b  and outer cylinder  312   a  or is welded or otherwise connected to end  312   b.    
     Cylinder  314  is located between cylinder elements  312   a  and  312   c . Cylinder  314  is in contact with end  312   b  of the double cylinder  312  at  314   b  by one or more pointed tip element(s)  314   a  or the like. Cylinder  314  is held so that it is not in contact with cylinder element  312   a  and  321   c  by being welded or otherwise firmly connected at point  314   b  or by insulating spacers or other means which will be understood by those skilled in the art. Leads  312   d  and  314   d  are connected to cylinders  312  and  314  respectively by clamps or the like not visible, but understood by those skilled in the art). 
     FIG. 9 shows a most useful and valuable embodiment of a thermocouple sensing device  400  to practice the method of this invention, In this embodiment a member  412  (a wire or the like) formed of the first of two dissimilar thermocouple metals is coated with a layer or skin of non electrical conducting material  420 . This layer or skin  420  is then covered by a skin  414  of the second of the two dissimilar thermocouple metals. Finally, a layer or skin  422  of a corrosion resistant material such as platinum or the like is applied over the skin  414 . A pair of leads  418  and  419  are connected to skin  414  and element  412  at  418   a  and  419   a  by means known to those skilled in the art. 
     The application of the various layers or skins over the element  412  and over succeeding layers or skins will be by plating, dipping, spraying, powder coating and other means known to those skilled in the art. In the application of the very first layer or skin  420  of non electrical conducting material over the element  412  a small area  416  at the end, or some other location on element  412  will not be coated, or the coating will be removed at that area  416  before applying coating  414  of the second of the two dissimilar thermocouple materials. This will make the connection between metals  412  and  414 . The layer or skin  422  can be of one material such as platinum or the like, or it may be a multi-layered skin of more than one coating. 
     In the various embodiments of this invention it is to be understood that normally lead wires and connections to the dissimilar metallic elements will normally be of the same metals as the respective elements. Also, where the lead wires or the like may pass through an electrically conductive shield or coating of material appropriate electrical insulation will be provided. These features will be clear to those skilled in the art. 
     In the claims which follow I may inadvertently fail to claim certain patentable features of this invention. In that event such failure to claim will be strictly unintentional and must not be interpreted as an intent to abandon or dedicate such features. In the event I shall discover that I have failed to claim any such features, I shall immediately seek to claim such features by re-issue or other appropriate means. 
     While the embodiments shown and described are fully capable of achieving the objects and advantages desired, such embodiments are for purposes of illustration and not for purposes of limitation.