Abstract:
A set of electrical connector pins for a thermocouple includes two materially similar conductor pairs, each conductor pair having conductors composed of a different material, and carried by an electrically insulating connector housing. The different materials of the conductor pairs provide a partial compensation to the thermocouple EMF developed between the hot junction and the cold junction when engaged thereto for the different type thermocouples. The conductors of each pair are operable to engage with two thermoelement conductors that form a thermocouple of differing types. The thermocouples provide a hot junction electrical interconnection therebetween at one end and are coupled to a cold junction at another end.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a divisional of U.S. patent application Ser. No. 10/463,135 filed on Jun. 17, 2003. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to thermocouples and more particularly to apparatus and systems for partially compensating the cold junction of a thermocouple system using low cost semi-compensated conductors.  
       BACKGROUND OF THE INVENTION  
       [0003]     Thermocouples are analog temperature sensors that utilize the thermoelectric properties of two dissimilar materials, typically metals, to generate an EMF in proportion to a temperature gradient across a material inhomogeneity. Common thermocouples used in temperature measurement comprise two metal wires of different thermoelectric properties called thermoelements connected at one end to form a “hot junction” also known as a “measuring junction”. The other ends of the wires are connected to instrumentation such as a voltmeter to measure the EMF produced by the thermocouple. The wires are connected to the instrumentation at a known reference temperature to form a “reference junction” or a “cold junction”. For the most precise measurements it is desirable that the only material inhomogeneity in the measurement circuit occurs at the measurement junction where the two dissimilar materials are joined.  
         [0004]     Because it is undesirable to have any other EMF sources between the measurement junction and the reference junction, it is important that there is a minimal temperature gradient across the thermoelectric material and the electrical instrumentation leads. Thermocouple materials are specialized alloys while electrical instruments typically utilize common metals such as copper, nickel, gold, beryllium copper, aluminum, and a variety of plating materials. This material inhomogeneity at the reference termination can lead to significant errors unless care is taken to minimize temperature gradients in this region or to accurately characterize the gradients that exist.  
         [0005]     In addition, thermocouple assemblies must use expensive hardware in the connection schemes at the termination end. Rather than using common contact materials such as copper, nickel, gold and others that are readily available, thermocouple connectors are made from more expensive thermocouple materials to minimize any inhomogeneity in the connector. A connector using thermocouple materials for the pins and sockets is referred to as a compensated connector. A compensated connector is designated to work only with a specific thermocouple type thus limiting the utility of the electronic instrumentation to only one type of sensor.  
         [0006]     In thermocouple temperature measurement it is important to accurately establish the temperature of the reference junction in order to determine the temperature of the measured junction. In industrial temperature measurement, a temperature sensor such as an RTD, thermistor, diode, transistor, or an IC chip type sensor measures the cold junction. In almost all instances there will exist a temperature gradient between the cold junction sensor location and the location of the thermocouple leadwire termination. This temperature gradient is usually traversed by non-thermocouple wires or circuit board traces that generate little or no EMF. The result of this is an error in the temperature measurement that is approximately equal to the size of the temperature gradient.  
         [0007]     A solution to the problem of a temperature gradient existing between the cold junction compensation (CJC) sensor and the thermocouple termination would be to use compensated materials for the lead connection and terminals. For example, a copper/constantan thermocouple (Type T) could use circuit board and terminals made from copper for the positive leg and constantan for the negative leg. This solution, however, has several negative aspects. The first and most obvious negative impact is the system is now only suitable for type T thermocouples because other types of thermocouples would experience an error from the different EMFs generated by the material differences. A second problem is a more practical problem of material availability. While copper is commonly available for terminals and printed circuit board traces, the other material, constantan, is not. Electrical hardware made from constantan or other common thermocouple alloys would be costly and would not be readily available.  
         [0008]     Accordingly, there is a need for compensating the cold junction of a thermocouple system using low cost materials for system components accommodating various thermocouple types.  
       SUMMARY OF THE INVENTION  
       [0009]     The following presents a simplified summary in order to provide a basic understanding of one or more aspects of the invention. This summary is not an extensive overview of the invention, and is neither intended to identify key or critical elements of the invention, nor to delineate the scope thereof. Rather, the primary purpose of the summary is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.  
         [0010]     The present invention is directed to a thermocouple system for partially compensating the cold junction of the system using low cost semi-compensated materially similar conductor pairs of system components, thereby enabling multiple thermocouple types to be universally applied to a single thermocouple monitoring system. The present invention further accommodates the application of a variety of conductor materials providing improved mechanical, electrical and thermal properties when used in connector terminals, pins, screws or other such system interconnection components while maintaining lower component costs and greater material availability.  
         [0011]     Current trends in electronics packages for thermocouples are leading toward a next generation thermocouple monitoring system capable of universally accommodating various types of thermocouple materials. Beneficially, the present invention takes a big step toward meeting this need in the thermocouple industry by establishing a system comprising interconnection conductors providing cold junction compensation compatible with multiple thermocouple material types.  
         [0012]     In conventional thermocouple systems, there are a number of interconnection junctions between the thermocouple and the monitoring instrumentation. For example, the thermocouple system may have junctions between the thermocouple leadwires and a pair of male connector pins, between the male connector pins and a pair of female connector pins, between the female connector pins and a printed circuit board, and potentially between the printed circuit board and the voltmeter.  
         [0013]     Each of these junctions offers an opportunity for producing a material inhomogeneity and an EMF (e.g., a voltage) corresponding to the thermal differential across the materials. Ideally, the EMF produced corresponds to that of the particular thermocouple. This problem is commonly addressed by either providing materials that generally match those of the thermocouple, called “fully compensated” system, or simply use a common unmatched conductor material throughout all the junctions after the thermocouple, forming a substantially “uncompensated” system. Generally speaking, all of the aforementioned junctions except the measuring junction are in the relative vicinity of the cold junction. Therefore it is the cold junction which is typically either fully compensated by matched material use or substantially uncompensated. The present invention addresses the benefits of semi-compensated conductors for a partially compensated thermocouple system having multiple thermocouple types.  
         [0014]     According to one aspect of the invention, a set of electrical connector pins for a thermocouple includes two materially similar conductor pairs, each conductor pair having conductors composed of a different material, and carried by an electrically insulating connector housing. The different materials of the conductor pairs provide a partial compensation to the thermocouple EMF developed between the hot junction and the cold junction when engaged thereto for the different type thermocouples. The conductors of each pair are operable to engage with two thermoelement conductors that form a thermocouple of differing types. The thermocouples provide a hot junction electrical interconnection therebetween at one end and are coupled to a cold junction at another end.  
         [0015]     According to another aspect of the invention, an electrical connector is configured for mating to a thermocouple. The electrical connector includes two materially similar elongated metallic conductor pairs, each conductor pair composed of two different metals. The different metals of each of the elongated metallic conductor pairs provide a partial compensation to the thermocouple EMF developed at the cold junction of the respective thermocouple when engaged thereto. The conductor pairs are operable to engage with two other mating pairs of connector conductors electrically connected to two different thermocouple types to provide a hot junction electrical interconnection therebetween at one end and couple to a cold junction at another end. Also included is an electrically insulating connector housing through which each conductor is carried with each conductor positioned to project from the connector housing.  
         [0016]     According to yet another aspect of the invention, an electrical connector is configured for mating to a thermocouple. The electrical connector includes two elongated metallic conductors. Each of the conductors is composed of a different material. The different metals of the conductors are adapted to provide a partial compensation to the thermocouple EMF developed at the cold junction of the thermocouple when engaged thereto. The conductors are operable to engage with two other mating connector conductors electrically connected to a thermocouple and provide a hot junction and electrical interconnection therebetween at one end and couple to a cold junction at another end. Also included is an electrically insulating connector housing. Each conductor is carried by the connector housing and is positioned to project from the connector housing.  
         [0017]     To the accomplishment of the foregoing and related ends, the following description and annexed drawings set forth in detail certain illustrative aspects and embodiments of the invention. These are indicative of but a few of the various ways in which the principles of the invention may be employed. Other aspects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]      FIG. 1  is a prior art diagram illustrating a conventional thermocouple device as provided by a thermocouple manufacturer such as may be used in a temperature monitoring system;  
         [0019]      FIG. 2  is an accompanying schematic symbol of the prior art thermocouple of  FIG. 1 , and the polarity of an EMF provided by the device;  
         [0020]      FIG. 3  is a chart of some of the properties of several thermocouple thermoelements such as may be used in the thermocouple system of the present invention;  
         [0021]      FIG. 4  is a diagram illustrating the temperature at various junctions of an exemplary fully compensated thermocouple system used for temperature monitoring, demonstrating the EMF detected using the thermoelements and conductors between each junction and the EMF produced by the CJC sensor;  
         [0022]      FIG. 5  is a diagram illustrating the temperature at various junctions of an exemplary uncompensated thermocouple system used for temperature monitoring, demonstrating the EMF detected using the thermoelements and conductors between each junction and the EMF produced by the CJC sensor;  
         [0023]      FIG. 6  is a diagram illustrating the temperature at various junctions of an exemplary semi-compensated thermocouple system for temperature monitoring in accordance with the present invention, demonstrating the EMF detected using the thermoelements and conductors between each junction and the EMF produced by the CJC sensor;  
         [0024]      FIG. 7  is a diagram illustrating the temperature at various junctions of another exemplary semi-compensated thermocouple system for temperature monitoring in accordance with the present invention, demonstrating the EMF detected using the thermoelements and conductors between each junction and the EMF produced by the CJC sensor;  
         [0025]      FIG. 8  is a chart of some of the properties and relative merits of several exemplary thermocouple system conductors such as may be used in a variety of connectors of the TC systems of the present invention for partially compensating the cold junction in accordance with several aspects of the present invention;  
         [0026]      FIGS. 9-10  illustrate several exemplary TC systems in accordance with various aspects of the present invention wherein the semi-compensating conductors of  FIG. 8  and other such conductor combinations may be used;  
         [0027]      FIGS. 11-13  illustrate a TC system comprising multiple TC types, having a semi-compensation portion with materially similar conductor pairs, in accordance with the present invention; and  
         [0028]      FIG. 14  is a diagram illustrating the temperature at various junctions of yet another exemplary semi-compensated thermocouple system for temperature monitoring using a screw terminal strip connector in accordance with the present invention, demonstrating the EMF detected using the thermoelements and conductors between each junction and the EMF produced by the CJC sensor.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]     The present invention will now be described with reference to the attached drawings, wherein like reference numerals are used to refer to like elements throughout. The invention relates to a thermocouple measurement system for partially compensating the cold junction of the system using materially similar pairs of system components comprising low cost conductors, thereby enabling multiple thermocouple types to be universally applied to a single thermocouple monitoring system.  
         [0030]     Conventionally, expensive thermoelements may be used to fully compensate the junctions of a TC system. Alternately, conventional systems may not use any cold junction compensation rather than absorb the high cost of thermoelement based connection hardware. The thermocouple system of the present invention, rather, strikes a midway approach to either of these extremes, and in the process further presents a solution that provides a thermocouple system that is equally suited to a variety of TC material types. In order to better appreciate one or more features of the invention, several exemplary implementations of the temperature monitoring system, the thermoelements, some of the semi-compensation conductors and the benefits of each are hereinafter illustrated and described with respect to the following figures.  
         [0031]      FIG. 1  illustrates a conventional thermocouple device  100 , such as may be provided by a thermocouple manufacturer and used in a temperature monitoring system, while  FIG. 2  illustrates an accompanying schematic symbol  200  of the thermocouple of  FIG. 1 . Most common thermocouples are temperature measuring devices or sensors comprising two dissimilar metals connected together at one end, called the hot junction. The two metals have a polarity with respect to each other and one of these is referred to as the positive leg and the other as the negative leg. The two free ends, called the cold end, generate a voltage (EMF) proportional to the temperature difference between the hot end and the cold end.  
         [0032]     Referring back to  FIG. 1 , the conventional thermocouple typically has a stainless steel sheath  110  for protection over the hot junction that may be potted therein (e.g., a ceramic, or epoxy potting material), together with a transition  120  (e.g., stainless steel) to protect the transition to a length of high temperature insulated leadwire  130 . The leadwire  130  may also have a length of heatshrink protection and a label  140  before it terminates in a mini-plug connector  145 .  
         [0033]      FIG. 3  illustrates a chart  300  of some of the properties of several thermocouple thermoelements such as may be used in a variety of thermocouple systems including the TC system of the present invention. Many of the more commonly used thermoelement combinations have been assigned letter designations (e.g., J, K, and T) for easy reference to their more complex material and elemental compositions shown. Each thermoelement material combination has a more positive and a more negative polarity based on the thermal characteristics of each element which provides an EMF, identified as the Seebeck Coefficient, as a function of the thermal differential between the hot and cold junction of each TC type. Each TC combination also has a useful operating temperature range, also based on the thermal and mechanical characteristics of the elemental compositions.  
         [0034]     For example, the K type thermocouple is comprised of a nickel-chrome (+) thermoelement (typically in the form of a wire) joined to a nickel-aluminum-silicon (−) thermoelement. Nickel-chrome is the more positively polarized type K thermoelement (KP) comprising Nickel and Chromium, while the more negatively polarized Nickel-aluminum-silicon thermoelement (KN) comprises Nickel, Aluminum and Silicon. This TC combination provides a Seebeck Coefficient of approximately 0.041 mV/° C. over a 0-1260° C. temperature range. This may best be appreciated in the following figures.  
         [0035]      FIGS. 4-7  illustrate several diagrams of the temperature at various junctions of several types of thermocouple systems used for temperature monitoring.  FIGS. 4-7  also illustrate the EMF detected using the thermoelements and conductors between each junction and the EMF produced by a CJC sensor that is typically located as close as possible to the cold junction for measuring the cold junction temperature.  
         [0036]      FIG. 4 , for example, illustrates a diagram of an exemplary fully compensated thermocouple system  400  used for temperature monitoring. As previously discussed, in current thermocouple systems, there are a number of interconnection junctions between the thermocouple and the monitoring instrumentation. In  FIG. 4 , for example, the thermocouple system  400  comprises a type K thermocouple measuring junction  405  and may have junctions  410   a,    410   b  in the type K positive (KP) leadwire  415   a  and negative (KN) leadwire  415   b,  respectively, between the thermocouple leadwires  415  and a pair of male connector pins KP  420   a  and KN  420   b.    
         [0037]     The KP notation on both sides of junction  410   a,  and the KN on both sides of junction  410   b  indicate that no material inhomogeneity has taken place at these junctions between the TC leadwire and the male connector pins. The fully compensated TC system  400  has another junction  425   a,    425   b  between the male connector pins KP  420   a  and KN  420   b  and a pair of female connector pins KP  430   a,  KN  430   b,  again with no material inhomogeneity. Finally, the fully compensated TC system  400  has a junction  435   a,    435   b  between the female connector pins KP  430   a,  KN  403   b  and a printed circuit board. The printed circuit board PCB typically has copper printed circuit traces  440   a,    440   b  that are eventually connected to a voltmeter  450 . This final female connector to PCB junction  435  is the only junction in the system with a material inhomogeneity or a material transition  455 .  
         [0038]     Although there is a material transition  455  at this junction  435   a,    435   b,  because a CJC sensor is utilized at this junction establishing a known reference temperature, the cold junction is said to be fully compensated to this point.  
         [0039]     In  FIGS. 4-7 , exemplary temperature zones (T 1 -T 4 ) are illustrated at four identified junctions of the systems and the EMFs produced by the dissimilar materials (thermoelements and conductors) between each junction and the EMF produced by the CJC sensor. The four identified junctions of the system also divide the system into four basic sections or portions, a TC portion  460 , a TC male connector  465 , a PC board female connector  470 , and the PC board CJC Portion  475 . The four temperature zones chosen are: a 100° C. measurement temperature  480  at the TC thermocouple junction (e.g.,  405  of  FIG. 4 ), a 30° C. temperature  485  at the TC to TC male connector junction (e.g.,  410   a,    410   b  of  FIG. 4 ), a 25° C. temperature  490  at the TC male to PCB female connector junction (e.g.,  425   a,    425   b  of  FIG. 4 ), and a 20° C. temperature  495  at the PCB female to PCB CJC portion junction (e.g.,  435   a,    435   b  of  FIG. 4 ).  
         [0040]     Given these temperature differentials and the TC materials used, the EMF produced in each section of the fully compensated system of  FIG. 4  is as follows:  
                                           Area   Material   Temp differential   EMF                   TC Portion   K   T1 = (100 − 30)° C. = 70° C.   =2.893 mV       TC Male Conn.   K   T2 = (30 − 25)° C. = 5° C.   =0.203 mV       PCB Female   K   T3 = (25 − 20)° C. = 5° C.   =0.202 mV       Conn.       PCB CJC Portion   CJC   T4 = (20 − 0)° C. = 20° C.   =0.798 mV               TOTAL =   =4.096 mV                  
 
 Since a type K thermocouple produces 4.096 mV at 100° C., there is no error produced by the fully compensated TC system having a single material inhomogeneity  455  after that of the TC measurement junction  405 , and then only at the cold junction. 
 
         [0041]     By contrast,  FIG. 5  illustrates an exemplary uncompensated thermocouple system  500  used for temperature monitoring. This TC system  500  is illustrated similar to that of  FIG. 4  except that the only thermoelements used in the system are the thermoelements KP  415   a,  KN  415   b  used in the type K thermocouple itself of the TC portion  460 . For example, a single conductor such as copper  520  is used throughout the rest of the system  500  from junction  510   a,    510   b,  to a connector junction  525   a,    525   b,  to the CJC junction  535   a,    535   b.  Therefore the uncompensated system  500  of  FIG. 5 , also has only one junction of material inhomogeneity  555  after that of the TC measurement junction  405 . As previously discussed, the problem here is that no EMF is generated across the homogenous material junctions to compensate the actual temperature differentials across those conductors.  
         [0042]     Given the same temperature differentials, and the TC materials used in accordance with the uncompensated system of  FIG. 5 , the EMF produced in each section is as follows:  
                                           Area   Material   Temp differential   EMF                   TC Portion   K   T1 = (100 − 30)° C. = 70° C.   =2.893 mV       TC Male Conn.   Cu   T2 = (30 − 25)° C. = 5° C.   =0.000 mV       PCB Female   Cu   T3 = (25 − 20)° C. = 5° C.   =0.000 mV       Conn.       PCB CJC Portion   CJC   T4 = (20 − 0)° C. = 20° C.   =0.798 mV               TOTAL =   =3.691 mV                  
 
 Since a type K thermocouple produced 3.691 mV due to the thermal EMFs representing 90° C. while the actual temperature is 100° C., there is an error of 10° C. produced by the uncompensated TC system of  FIG. 5 , having a single material inhomogeneity  545  after the TC measurement junction  405 , and does not reside at the cold junction. Although this system is much less expensive than that of the fully compensated system of  FIG. 4 , a significant error is also likely. 
 
         [0043]     A better solution to these extremes is the use of common materials to create semi-compensated terminations, for example, in the conductors or terminal pins of the connectors discussed. Semi-compensated electrical hardware of the present invention generate a portion of the EMF expected from common thermocouple types over any temperature gradient existing between the CJC sensor and the electrical termination. For instance, electrical hardware using copper for the positive leg connections and nickel for the negative leg connection yields a combination Cu/Ni Seebeck coefficient of:  
                                                       Cu =     0.0076 mV/° C.           Ni =   −0.0148 mV/° C.           Cu—Ni =     0.0224 mV/° C.                      
 
         [0044]     This Cu—Ni combination produces about half the EMF output of a type K thermocouple that produces roughly 0.041 mV/° C. near room temperature. Thus the semi-compensated materials would correct about ½ of the EMF of a type K thermocouple. While this is not a perfect compensation it has the advantage of being made from common materials and being applicable to a variety of other thermocouple types. A type J thermocouple has around 0.06 mV/° C. and so the semi-compensated conductors (e.g., pins, terminals, etc.) would recover around a third of any error associated with a temperature gradient across a junction or connector inhomogeneity.  
         [0045]      FIGS. 6 and 7 , for example, illustrate exemplary semi-compensated thermocouple systems  600  and  700 , respectively, for partially compensated temperature monitoring in accordance with the present invention.  FIGS. 6 and 7  provide junctions between each of the same four areas or portions of the system as identified previously in  FIGS. 4 and 5 , namely: the TC portion  460 , the TC male connector region  465 , the PC board female connector region  470 , and the PC board CJC portion  475 .  FIGS. 6 and 7  are also illustrated using the same four temperatures: 100° C. at  480 , 30° C. at  485 , 25° C. at  490 , and 20° C. at  495 , as used in  FIGS. 4 and 5 .  
         [0046]     By contrast to either the fully compensated or the uncompensated TC system, semi-compensation is provided by the choice of the conductors used between the TC portion  460  and the PC board CJC portion  475 , that is, in what is termed herein, the “semi-compensated portion”, or SC portion. The SC portion is further defined and bounded by at least two junctions having material inhomogeneities (e.g.,  645  and  655  of  FIG. 6 , or  745  and  755  of  FIG. 7 ).  
         [0047]     For example, in  FIG. 6 , junction  610   a,    610   b  transitions from KP/KN to Cu/Ni, respectively. Although  645  is a material inhomogeneity, an EMF is still produced traversing conductors  620 A,  620   b  and  630   a,    630   b  within the connectors  465  and  470  because the materials of conductors  620   a  and  620   b  are dissimilar, and because the materials of conductors  630   a  and  630   b  are dissimilar (e.g., Cu vs. Ni, respectively). Thus, the material inhomogeneities  645  and  655  of the exemplary TC system of  FIG. 6  define an SC portion for partially compensating the cold junction.  
         [0048]     Using the same temperature differentials as before, and the TC materials and conductor materials of the semi-compensated system of  FIG. 6 , the EMF produced in each section is as follows:  
                                           Area   Material   Temp differential   EMF                   TC Portion   K   T1 = (100 − 30)° C. = 70° C.   =2.893 mV       TC Male Conn.   Cu/Ni   T2 = (30 − 25)° C. = 5° C.   =0.112 mV       PCB Female   Cu/Ni   T3 = (25 − 20)° C. = 5° C.   =0.112 mV       Conn.       PCB CJC Portion   CJC   T4 = (20 − 0)° C. = 20° C.   =0.798 mV               TOTAL =   =3.915 mV                  
 
 Since a type K thermocouple produces 3.915 mV due to thermal EMFs representing 95° C. while the actual temperature is 100° C., there is an error of 5° C. produced by the semi-compensated TC system of  FIG. 6 , having at least two material inhomogeneities  645  and  655  after the TC measurement junction  405 . The semi-compensated system  600  is still much less expensive than that of the fully compensated system  400  of  FIG. 4 , but only produces half the error of the uncompensated system  500  of  FIG. 5 . In addition to providing the cost advantage, other mechanical, electrical, and thermal benefits of the Cu/Ni combination and other semi-compensating conductor combinations are obtained and will be discussed in more detail in association with  FIG. 8 . 
 
         [0049]     In another semi-compensation example of the present invention illustrated in  FIG. 7 , junction  710   a , 710   b  may retain the type K materials in the TC male connector  465  conductors KP  720   a  and KN  720   b,  then at junction  725   a  and Ni  730   b,  respectively, producing a material inhomogeneity  745 . Again, although  745  is a material inhomogeneity, an EMF is still produced traversing conductors  720   a,    720   b  and  730   a,    730   b  within the connectors  465  and  470  because the materials of conductors  720   a  and  720   b  are dissimilar, and because the materials of conductors  730   a  and  730   b  are dissimilar (e.g., Cu vs. Ni, respectively). Thus, the material inhomogeneities  745  and  755  of the exemplary TC system of  FIG. 7  define an SC portion for partially compensating the cold junction.  
         [0050]     Using the same temperature differentials as before, and the TC materials and conductor materials of the semi-compensated system of  FIG. 7 , the EMF produced in each section is as follows:  
                                           Area   Material   Temp differential   EMF                   TC Portion   K   T1 = (100 − 30)° C. = 70° C.   =2.893 mV       TC Male Conn.   K   T2 = (30 − 25)° C. = 5° C.   =0.203 mV       PCB Female   Cu/Ni   T3 = (25 − 20)° C. = 5° C.   =0.112 mV       Conn.       PCB CJC Portion   CJC   T4 = (20 − 0)° C. = 20° C.   =0.798 mV               TOTAL =   =4.006 mV                  
 
 Since a type K thermocouple produces 4.006 mV due to thermal EMFs representing 97.5° C. while the actual temperature of 100° C., there is an error of only 2.5° C. produced by the semi-compensated TC system of  FIG. 7 , having at least two material inhomogeneities  745  and  755  after the TC measurement junction  405 . The semi-compensated system  700  is still less expensive than that of the fully compensated system  400  of  FIG. 4 , but only produces one quarter of the error of the uncompensated system  500  of  FIG. 5 . 
 
         [0051]     Thus, several electrical and economic benefits of using common semi-compensating conductor materials for the junctions of a single TC type measurement system have been shown. However, further economic and user advantages are available in providing a TC monitoring system, in accordance with the present invention, wherein the same pair combination of conductor materials is used for a TC system having multiple TC types. In particular, it is advantageous for the user of the system to be able to plug any number of a list of thermocouples into the same thermocouple receptacles, as well as less expensive for the manufacturer to supply a connector, screws or pins, for example, with common and more readily available hardware materials.  
         [0052]     To avoid the electrical loss of uncompensated hardware, and the high cost and poor material availability of fully compensated hardware, the present invention attempts to provide a system using materially similar pairs of common conductor materials for receiving multiple TC types. For example, as will be further shown in association with the following figures, two various types (e.g., type J, T, K, N, S) of thermocouples may be both interconnected into a TC system using two pairs of Cu vs. Ni semi-compensating conductor hardware.  
         [0053]     There are a variety of material combinations for semi-compensated conductors or pins including aluminum vs. nickel with a Seebeck coefficient of around 0.019 mV/° C., or palladium vs. platinum at 0.006 mV/° C. Thus, a variety of semi-compensation levels are available to accommodate various requirements of the system as shown in the following figure.  
         [0054]      FIG. 8 , for example, illustrates a chart  800  of several exemplary semi-compensation conductor combinations that may be used for partially compensating the cold junction of the TC systems in accordance with several aspects of the present invention. The list of semi-compensation conductors is ordered from lowest to highest Seebeck coefficient. Chart  800  further compares some of the properties and relative merits of the exemplary semi-compensation conductor combinations such as may be applicable to a variety of pins, terminals, and screw connectors and terminal strips, however, copper and nickel appear to be one of the more preferred embodiments.  
         [0055]     In addition, the specific combination of semi-compensation conductors may be selected in accordance with an aspect of the present invention to best coordinate with the range of Seebeck coefficients of the thermocouples used, to provide a particular level of compensation desirable for the TC system application. If, for example, a TC System uses a type J and a type K thermocouple, another set of semi-compensated conductors could be selected for the TC system, which provided a Seebeck coefficient midway between that of the type J and K thermocouples, yet had good cost, mechanical, electrical and thermal properties similar to those of the Cu/Ni combination, a higher level of semi-compensation may be attained for the TC system at a low cost.  
         [0056]     For example, an Iron/Nickel combination would be the best choice from  FIG. 8  with the highest Seebeck coefficient output of 0.035 mV/° C. to coordinate with the type J and K thermocouple Seebeck coefficients of 0.06 mV/° C. and 0.041 mV/° C., respectively, but the Fe/Ni combination may have poor electrical and thermal properties compared to the use of Cu/Ni that may outweigh the EMF advantage of Fe/Ni in many applications. Although the Cu vs. Ni conductor combination has been shown and described in the examples and figures of the invention, a variety of other combinations of semi-compensation conductors including metals, alloys, and metal or alloy platings and depositions are also anticipated in the context of the present invention.  
         [0057]      FIGS. 9-14  illustrate several exemplary TC systems in accordance with various aspects of the present invention and  FIGS. 6 and 7 , wherein the semi-compensating conductors of  FIG. 8  and other such conductor combinations may be used to partially compensate a cold junction of the system. A variety of pins, terminals, and screws of connectors and terminal strips are used in the TC systems illustrated in the figures, wherein one or more semi-compensation conductor combinations may be utilized.  FIGS. 11-13  illustrate a TC system comprising multiple TC types, having a semi-compensation portion with materially similar conductor pairs, in accordance with the present invention. Although  FIGS. 9, 10  and  14  illustrate only one conductor pair of a multiple TC type system, it should be appreciated that other such TC types will also be coupleable to the conductor pair illustrated together with other conductor pairs, whereby semi-compensation of the system is accomplished.  
         [0058]      FIG. 9  illustrates an exemplary semi-compensated TC system  900 . TC system  900  uses a type K thermocouple sensor  905  having a male plug  910 . The male plug  910  engages a female connector  915  affixed to a printed circuit board (PCB)  920 . The positive KP (TC+) and negative KN (TC−) leadwires of the type K TC  905  are connected to a pair of male pins  925   a  and  925   b,  respectively, mounted in an insulative plug housing  930  of the male plug  910 . A junction  935   a,    935   b  having a material inhomogeneity is formed where the leadwires KP/KN join the male pins  925   a,    925   b  (e.g., Cu/Ni pins), respectively, mounted in an insulative receptacle housing  945  of the female receptacle  915 . Another junction is formed where the male pins  925   a,    925   b  engage the female pins  940   a,    940   b,  respectively. Typically, this junction will not, but may or may not have a material inhomogeneity.  
         [0059]     Another junction terms a cold junction  950   a,    950   b  having a material inhomogeneity is formed where the female pins  940   a,    940   b  (e.g., Cu/Ni pins) attach to the traces  955   a,    955   b  (e.g., typically copper traces), respectively, of the PCB  920 . Near, and usually between the junctions  950   a , 950   b,  where the female pins  940   a,    940   b  join the PCB  920 , a cold junction compensation CJC sensor  960  (e.g., an RTD, thermistor, diode, transistor, or an IC chip type sensor) is mounted to detect the temperature of the cold junction  950   a,    950   b  for CJC temperature correction of the TC system. PCB traces  965  attach to the CJC sensor  960  for external detection of the ambient temperature at the cold junction  950   a,    950   b.  Knowing the CJC temperature is usually critical to the accurate ambient temperature compensation of the system, so CJC sensor  960  may also be potted or otherwise thermally bonded near the cold junctions  950   a,    950   b.    
         [0060]     Thus, in the example of  FIG. 9 , two junctions ( 935   a,    935   b  and  950   a,    950   b ) having material inhomogeneities in accordance with the invention are present in the semi-compensated TC system  900 . TC system  900  utilizes semi-compensated conductor material combinations (e.g., Pd/Pt, Cu/Ni, Al/Ni, Au/Ni, and Fe/Ni) in the form of male and female pins  925   a,    925   b  and  940   a,    940   b,  respectively. The male and female pins in this example form the semi-compensated portion (SC portion) of the system  900  referred to in the system  600  of  FIG. 6 . If in this example Cu/Ni were used for the semi-compensation materials for these conductors, the error produced by the system would correspond to that of system  600  of  FIG. 6 . Alternately, if the male pins  925   a,    925   b  were comprised of KP/KN material, and only the female pins  940   a,    940   b  were comprised of the Cu/Ni semi-compensation conductor materials, the error produced by the system would correspond to that of system  700  of  FIG. 7 .  
         [0061]     Although a male plug/pins has been shown and described in the examples and figures of the invention in association with a thermocouple, and a female receptacle/pins has been used in association with a PCB, a female plug/pins used in association with the thermocouple, and a male receptacle/pins used in association with the PCB or wiring to another such circuit is also anticipated in the context of the present invention.  
         [0062]      FIG. 10  illustrates another exemplary semi-compensated TC system  1000 . TC system  1000  is similar to that of TC system  900  of  FIG. 9  in many ways and therefore need not be described again in detail except where the systems differ. For example, system  1000  again is illustrated using a type K thermocouple sensor  1005  attached to a plug  1010  that engages a receptacle  1015  affixed to a printed circuit board (PCB)  1020 . In this example, the plug  1010  and receptacle  1015  are configured as PCB mounted pin/socket header type connectors. The positive and negative leadwires KP/KN of the type K TC  1005  are connected to a pair of female pins  1025   a  and  1025   b  this time, respectively, mounted in an insulative plug housing  1030  of the plug  1010 . A junction  1035   a,    1035   b  having a material inhomogeneity is formed where the KP/KN leadwires join the female pins  1025   a,    1025   b  (e.g., Al/Ni pins), respectively. The female pins  1025   a,    1025   b  engage male pins  1040   a,    1040   b  (e.g., Al/Ni pins), respectively, mounted in an insulative receptacle housing  1045  of the receptacle  1015 . Another junction is formed where the male pins  1025   a,    1025   b  engage the female pins  1040   a,    1040   b,  respectively.  
         [0063]     A cold junction  1050   a,    1050   b  having the second material inhomogeneity is formed where the male pins  1040   a,    1040   b  (e.g., Al/Ni pins) attached to the traces  1055  (e.g., typically copper traces) of the PCB  1020 . A cold junction compensation CJC sensor  1060  (e.g., an RTD, thermistor, diode, transistor, or an IC chip type sensor) is mounted near the PCB junctions  1050   a,    1050   b  of the male pins  1040   a,    1040   b  to detect the temperature of the cold junction  1050   a,    1050   b  for CJC temperature correction of the TC system  1000 .  
         [0064]     Thus, in the example of  FIG. 10 , two junctions ( 1035   a,    1035   b  and  1050   a,    1050   b ) having material inhomogeneities in accordance with the invention are formed in the semi-compensated TC system  1000 . Again, the TC system  1000  utilizes semi-compensated conductor material combinations (e.g., Pd/Pt, Cu/Ni, Al/Ni, Au/Ni or Fe/Ni) in the form of female and male pins  1025   a,    1025   b  and  1040   a,    1040   b,  respectively, thus forming the SC portion of the system  1000  similar to that of system  600  of  FIG. 6  or system  700  of  FIG. 7 .  
         [0065]     The pin headers of  FIG. 10  may provide an additional benefit, where multiple TCs are to be interconnected to a single PCB, as each pair of pins/sockets of the mating headers offering an additional opportunity to engage another TC in a compact layout. The small conductor lengths of the male and female pins also tend to minimize thermal differentials in the exemplary TC system.  
         [0066]      FIG. 11  illustrates an exemplary TC system  1100  comprising multiple TC types, in accordance with the present invention. TC system  1100  comprises a TC portion  1110  having two or more TC types (e.g., 4 types) for example, TC 1  is a type J thermocouple  1111 , TC 2  is a type T thermocouple  1112 , TC 3  is a type K thermocouple  1113 , and TC 4  is a type S thermocouple  1114 . System  1100  further comprises a semi-compensation portion  1120  having materially similar conductor pairs  1121 , for example, comprising semi-compensating conductor pairs (e.g., Au/Ni, Cu/Ni, Pd/Pt)  1121  that are materially similar for all the TC types used in the system.  
         [0067]     Each TC of the multiple TC type system  1100  is coupled to one of the materially similar conductor pairs  1121 , wherein one of the conductors of each pair  1121  is composed of a material different than the thermoelectric materials of the TC portion  1110 . System  1100  also comprises a cold junction compensation portion CJC  1130  using the same conductor material throughout all the conductor pairs, for example, conductor pairs  1131  all comprise one material type (e.g., Cu, Ag, Au). The CJC portion  1130  further comprises one or more thermal sensors (not shown) near the junction of the semi-compensation portion  1120  and the CJC portion conductor pairs  1131 , wherein multiple semi-compensated temperature measurement outputs  1140  may be provided.  
         [0068]     For example,  FIG. 12  illustrates an exemplary TC system  1200  comprising multiple TC types, in accordance with the present invention and TC system  1100  of  FIG. 11 , which is similar to that of  FIG. 12 , and as such need not be described again in full detail except where noted. TC system  1200  also comprises a TC portion  1210  having, for example, four TC types  1210   a,  TC 1  is a type J thermocouple  1211 , TC 2  is a type T thermocouple  1212 , TC 3  is a type K thermocouple  1213 , and TC 4  is a type S thermocouple  1214 . Although four different TC types are illustrated in  FIG. 12 , any number or combination of each TC type or other such TC types may be used as desired.  
         [0069]     System  1200  further comprises a semi-compensation portion  1220  having materially similar conductor pairs, for example, a pair of Cu and Ni conductors  1221  comprise the semi-compensating conductor pairs (e.g., Au/Ni, Cu/Nl, Pd/Pt) that are materially similar for al the TC types  1210   a  used in the system  1200 . Each TC of the multiple TC type system  1200  is coupled at junction  1222  to one of the materially similar conductor pairs  1221 , wherein one of the conductors of each pair  1221  is composed of a material different than the thermoelectric materials of the TC portion  1210 . In the illustration, the SC portion  1220  also exemplifies a TC male connector  1220   a  and TC female connector  1220   b  having metallic conductors, or other such conductive hardware for engaging forming a junction  1225  therebetween.  
         [0070]     System  1200  also comprises a cold junction compensation portion CJC  1230  using the same conductor material throughout all the conductor pairs, for example, conductor pairs  1231  all comprise one material type e.g., Cu, Ag, Au). The CJC portion  1230  further comprises one or more thermal sensors (not shown) near the junction  1235  of the semi-compensation portion  1220  and the CJC portion conductor pairs  1231 , wherein multiple semi-compensated temperature measurement outputs  1240  may be provided. For example, the multiple semi-compensated outputs  1240  maybe coupled to a multiplexing analog to digital converter ADC  1250  for further measurement processing, output, or display. The connector configuration of  FIG. 10 , for example, illustrates one element of such a multiple TC type system. Connector bodies  1030  and  1045 , for example, maybe PCB mounted headers manufactured using any one of a variety of common semi-compensating conductor pairs (e.g.,  1025   a,    1025   b,  and  1040   a,    1040   b ) for interconnecting the TC types to the cold junctions.  
         [0071]      FIG. 13  illustrates another exemplary semi-compensated TC system  1300 . TC system  1000  is somewhat different from the TC systems of  FIGS. 9 and 10 . A screw terminal strip mounted to a PC board replaces plugs and receptacles, while a screw and terminal conductors replace the male and female pin conductors. By eliminating the plug from the TC system, the screw terminal strip also benefits thee system by eliminating one junction, namely, the leadwire to plug junction (e.g.,  935  of  FIG. 9 , or  1035  of  FIG. 10 ). This is because the screw head presses the TC+/TC− leadwires directly into the terminal conductor, without an additional plug junction. Similar to the header configuration of  FIG. 10 , the terminal strip of  FIG. 13  offers an in-line configuration suitable for multiple TC connections, as shown.  
         [0072]     In one example, the semi-compensated TC system  1300  of  FIG. 13  comprises a type J thermocouple TC 1   1305 , and a type T thermocouple TC 2   1310 , whose thermoelement leadwires are wired to a screw terminal trip having screw and terminal conductor pairs comprising semi-compensating conductor material combinations (e.g., Pd/Pt, Cu/Ni, Al/Ni, Au/Ni, and Fe/Ni). For example, the TC+ lead wires may be retained by Au or Au plated screws  1315   a  and  1320   a  and terminal conductors  1325   a  and  1320   a,  while the TC-lead wires may be retained by Ni or Ni plated screws  1315   b  and  1320   b  and terminal conductors  1325   b  and  1320   b  to the terminal strip  1335 , respectively. The terminal strip  1335  is attached with conventional screw hardware  1340  to the PCB  1345 .  
         [0073]     From this point, the terminal conductors  1325   a,    1325   b  and  1330   a,    1330   b  are joined to conductive traces  1350   a,    1350   b  and  1355   a,    1355   b  of the PCB  1345 . Once the terminal conductor is joined to the PCB conductive traces, the remaining portion of the system may be described similar to that of  FIGS. 9 and 10 , therefore need not be described again in detail except where the systems differ. CJC temperature sensors  1360  and  1365  are located near the cold junction terminals  1370  of the TC 1  type J  1305  and the TC 2  type T  1310  thermocouples, respectively. PCB traces  1370   a,    1370   b  and  1375   a,    1375   b  attach to the CJC sensors  1360  and  1365 , respectively, for external detection of the ambient temperature at the cold junctions  1370 .  
         [0074]      FIG. 14  illustrates a diagram  1400  of the exemplary semi-compensated thermocouple system  1300  of  FIG. 13 , using a screw terminal strip in accordance with the present invention.  FIG. 14  is illustrated and may be described similar to that of the TC system  700  of  FIG. 7 , and as such need not be fully described again for the sake of brevity. System  1400  demonstrates that the EMF detected from type K thermocouple  405  at 100° C.  480  is conveyed over leadwires KP/KN  415   a,    415   b  directly to a junction  1425   a,    1425   b  at 25° C.  490 , having a first material inhomogeneity  1427 , to a semi-compensating conducting material combination (e.g., Cu/Ni, or Au/Ni) comprising the screws and terminal conductors  1430   a,    1430   b.  The screws and terminal conductors  1430   a,    1430   b  terminate into a PC board forming another junction  1435   a,    1435   b  having a second inhomogeneity  1437  transitioning to conductive copper traces  1440   a,    1440   b  on the PCB, wherein the temperature is determined by voltmeter  450 .  
         [0075]     The TC system  1400  of  FIG. 14 , for example, like the system  1300  of  FIG. 13  uses a screw terminal strip comprising semi-compensating conductive material combinations in the screws and terminal conductors to compensate the cold junction of the TC system. In this exemplary system  1400 , three portions exist: a TC portion  1460 , a screw terminal conductor portion  1470 , and a PC board CJC portion  1475 .  
         [0076]     Using the temperature differentials indicated as before, and the TC materials and conductor materials of the semi-compensated system of  FIG. 14 , the EMF produced in each section is as follows:  
                                           Area   Material   Temp differential   EMF                   TC Portion   K   T1 + T2 = (100 − 25)° C. = 75° C.   =3.096 mV       Screw TS   Cu/Ni   T3 = (25 − 20)° C. = 5° C.   =0.112 mV       Conductor       PCB CJC   CJC   T4 = (20 − 0)° C. = 20° C.   =0.798 mV       Portion                           TOTAL =   =4.006 mV                  
 
 Since a type K thermocouple produces 4.006 mV due to thermal EMFs representing 97.5° C. while the actual temperature is 100° C., there is an error of only 2.5° C. produced by the semi-compensated TC system of  FIG. 14  (which is the same as in  FIG. 7 ), having at least two material inhomogeneities  1427  and  1437  after the TC measurement junction  405 . The semi-compensated system  1400  is still less expensive than that of the full compensated system  400  of  FIG. 4 , or that of system  700  of  FIG. 7 , but only produces one quarter of the error of the uncompensated system  500  of  FIG. 5  
 
         [0077]     Although the invention has been illustrated and described with respect to one or more embodiments, implementations, equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described components (assemblies, devices, circuits, systems, etc.), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (e.g., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary implementations of the invention. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.”