Patent Publication Number: US-2023134684-A1

Title: Modular heater assembly with interchangeable auxiliary sensing junctions

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. Serial application Ser. No. 16/840,766, filed Apr. 6, 2020 and titled “Modular Heater Assembly With Interchangeable Auxiliary Sensing Junctions”, which is a continuation-in-part application of U.S. Serial application Ser. No. 15/950,358, filed Apr. 11, 2018 and titled “Resistive Heater with Temperature Sensing Power Pins and Auxiliary Sensing Junction”, which is a continuation-in-part application of U.S. Serial application Ser. No. 14/725,537, filed May 29, 2015 and titled “Resistive Heater with Temperature Sensing Power Pins,” the content of which are incorporated herein by reference in their entirety. 
    
    
     FIELD 
     The present disclosure relates to resistive heaters and to temperature sensing devices such as thermocouples. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Resistive heaters are used in a variety of applications to provide heat to a target and/or environment. One type of resistive heater known in the art is a cartridge heater, which generally consists of a resistive wire heating element wound around a ceramic core. A typical ceramic core defines two longitudinal bores with power/terminal pins disposed therein. A first end of the resistive wire is electrically connected to one power pin and the other end of the resistive wire electrically connected to the other power pin. This assembly is then inserted into a tubular metal sheath of a larger diameter having an open end and a closed end, or two open ends, thus creating an annular space between the sheath and the resistive wire/core assembly. An insulative material, such as magnesium oxide (MgO) or the like, is poured into the open end of the sheath to fill the annular space between the resistive wire and the inner surface of the sheath. 
     The open end of the sheath is sealed, for example by using a potting compound and/or discrete sealing members. The entire assembly is then compacted or compressed, as by swaging or by other suitable process, to reduce the diameter of the sheath and to thus compact and compress the MgO and to at least partially crush the ceramic core so as to collapse the core about the pins to ensure good electrical contact and thermal transfer. The compacted MgO provides a relatively good heat transfer path between the heating element and the sheath and it also electrically insulates the sheath from the heating element. 
     In order to determine the proper temperature at which the heaters should be operating, discrete temperature sensors, for example thermocouples, are placed on or near the heater. Adding discrete temperature sensors to the heater and its environment can be costly and add complexity to the overall heating system. 
     SUMMARY 
     This section provides a general summary of the disclosure and is not a comprehensive disclosure of its full scope or all of its features. 
     In one form, a heater system is provided, which includes a plurality of heaters, a controller for supplying power to the plurality of heaters, a plurality sets of auxiliary wires extending from the plurality of heaters, and a wire harness for connecting the plurality sets of auxiliary wires to the controller. Each set of auxiliary wires includes three wires, two of the three wires being made of different materials and being joined to form a thermocouple junction, such that each of the plurality of heaters is operable to function as both a heater and a temperature sensor. 
     In other features, one of the at least three wires is made of a first conductive material, and the remaining ones of the wires are made of a second conductive material. The first conductive material is a copper-nickel alloy and the second conductive material is a nickel-chromium alloy. The plurality sets of auxiliary wires each include a temperature sensing wire, an auxiliary power supply wire, and an auxiliary power return wire, wherein the temperature sensing wire is joined to one of the auxiliary power supply wire and the auxiliary power return wire to form a thermocouple junction. The thermocouple junction is also joined to an end of a resistive heating element of each heater. The wire harness further includes a main power supply wire and a main power return wire directly connected to the controller, wherein one of the main power supply wire and the main power return wire is made of a same material of the temperature sensing wires. 
     In still other features, the heater system further includes a plurality of connectors directly connected to the plurality sets of auxiliary wires. The wire harness further includes a main power supply wire and a main power return wire, wherein the main power supply wire and the main power return wire are selectively connected to a same connector to route one of heaters as a stand-alone heater or selectively connected to different connectors such that at least some of the heaters are connected in series. 
     In another form, a power control system for controlling at least one heater is provided, which includes: a controller; a main power supply wire and a main power return wire directly connected to the controller; a first wire and a second wire connecting the at least one heater to the main power supply wire and the main power return wire. The main power supply wire and the first wire are connected and are made of a first conductive material. The main power return wire and the second wire are connected and are made of a second conductive material different from the first conductive material. 
     In other features, the first conductive material is a copper-nickel alloy, and the second conductive material is a nickel-chromium alloy. The power control system further includes at least one connector for connecting the main power supply wire and the main power return wire to the at least one heater. 
     In still other features, the power control system further includes a wire harness including a plurality of main power supply wires, a plurality of main power return wires, and a plurality of connectors corresponding to a plurality of heaters. The wire harness connects the controller to the plurality of heaters such that the plurality of heaters are connected in a series connection or as stand-alone heaters. The wire harness further includes a plurality of connecting wires for connecting the plurality of connectors such that the plurality of heaters are connected in series in different orders. 
     In still another form, a modular heater unit is provided, which includes a heater and a set of three wires extending from the heater. Two of the three wires are made of different materials and are joined to form a thermocouple junction. 
     In other features, the at least three wires include a temperature sensing wire made of a first conductive material, an auxiliary power supply wire and an auxiliary power return wire made of a second conductive material different from the first conductive material. The temperature sensing wire is joined to one of the auxiliary power supply wire and the auxiliary power return wire. The first conductive material is a copper-nickel alloy, and the second conductive material is a nickel-chromium alloy. The heater includes a resistive heating element, and the thermocouple junction is joined to an end of the resistive heating element. 
     In still other features, the modular heater unit further includes a connector part connected to the set of at least three wires. The connector part is configured to be connected to another connector part directly or via connecting wires. Only two of the set of at least three wires are connected to another electrical component to form a part of an electric circuit. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which: 
         FIG.  1    is a side cross-sectional view of a resistive heater with dual purpose power pins constructed in accordance with the teachings of the present disclosure; 
         FIG.  2    is a perspective view of the resistive heater of  FIG.  1    and a controller with lead wires constructed in accordance with the teachings of the present disclosure; 
         FIG.  3    is a circuit diagram illustrating a switching circuit and measurement circuit constructed in accordance with one form of the present disclosure; 
         FIG.  4    is a side cross-sectional view of an alternate form of the heater having a plurality of heating zones and constructed in accordance with the teachings of the present disclosure; 
         FIG.  5    is a side elevational view of an alternate form of the present disclosure illustrating a plurality of heaters connected in sequence and constructed in accordance with the teachings of the present disclosure; 
         FIG.  6    is a side cross-sectional view of another form of the heater having a resistive element with a continuously variable pitch and constructed in accordance with the teachings of the present disclosure; 
         FIG.  7    is a side cross-sectional view of another form of the heater having a resistive element with different pitches in a plurality of heating zones and constructed in accordance with the teachings of the present disclosure; 
         FIG.  8    is a side cross-sectional view of a heat exchanger employing a heater and constructed in accordance with the teachings of the present disclosure; 
         FIG.  9    is a side cross-sectional view illustrating a layered heater employing the dual purpose power pins and constructed in accordance with the teachings of the present disclosure; 
         FIG.  10    is a flow diagram illustrating a method in accordance with the teachings of the present disclosure; 
         FIG.  11    is a perspective view of a heater for use in fluid immersion heating and constructed in accordance with the teachings of the present disclosure; 
         FIG.  12    is a side cross-sectional view of a portion of the heater of  FIG.  11    in accordance with the teachings of the present disclosure; 
         FIG.  13    is a graph illustrating exemplary differences in temperature at the various junctions of the heater of  FIG.  10    in accordance with the teachings of the present disclosure; 
         FIG.  14    is a perspective view of another form of the present disclosure having a plurality of heater cores in zones and constructed in accordance with the teachings of the present disclosure; 
         FIG.  15    illustrates a heater having a primary sensing junction in accordance with the teaching of the present disclosure; 
         FIG.  16    illustrates a heater having two primary sensing junctions in accordance with the teachings of the present disclosure; 
         FIGS.  17 A and  17 B  are perspective views of cartridge heaters having primary sensing junctions in accordance with teachings of the present disclosure; 
         FIG.  18    is a perspective via tubular heater having a primary sensing junction and a two-wire heating element in accordance with teachings of the present disclosure; 
         FIG.  19    illustrates a primary sensing junction with enhanced temperature measurement features in accordance with teachings of the present disclosure; 
         FIG.  20    is a schematic diagram of a heater system including a plurality of heaters and a power control system constructed in accordance with the teachings of the present disclosure, wherein the power control system includes a wire harness that connects the plurality of heaters in a first series connection to form a first modular heater assembly; 
         FIG.  21 A  is an enlarged view of portion A of  FIG.  20   ; 
         FIG.  21 B  is schematic diagram of a modular heater unit including a heater, a three-wire mechanism extending from the heater, and a connector part; 
         FIG.  22    is an electric diagram of  FIG.  20   ; 
         FIG.  23    is a schematic diagram of a heater system including a plurality of heaters and a power control system constructed in accordance with the teachings of the present disclosure, wherein the power control system includes a wire harness that connects the plurality of heaters in a second series connection to form a second modular heater assembly; 
         FIG.  24    is a schematic diagram of a heater system including a plurality of heaters and a power control system constructed in accordance with the teachings of the present disclosure, wherein the power control system includes a wire harness that connects the plurality of heaters in a third series connection to form a third modular heater assembly; 
         FIG.  25    is a schematic diagram of a heater system including a plurality of heaters and a power control system constructed in accordance with the teachings of the present disclosure, wherein the power control system includes a wire harness that connects the plurality of heaters into a stand-alone heater and a fourth modular heater assembly; 
         FIG.  26    is an electric diagram of  FIG.  25   ; 
         FIG.  27    is an electric diagram of a heater system including a plurality of heaters and a power control system constructed in accordance with the teachings of the present disclosure, wherein the power control system includes a wire harness that connects the plurality of heaters into a stand-alone heater and a fifth modular heater assembly; and 
         FIG.  28    is an electric diagram of a heater system including a plurality of heaters and a power control system constructed in accordance with the teachings of the present disclosure, wherein the power control system includes a wire harness that connects the plurality of heaters into a stand-alone heater and a sixth modular heater assembly. 
     
    
    
     The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
     Referring to  FIG.  1   , a heater according to the teachings of the present disclosure is illustrated and generally indicated by reference numeral  20 . The heater  20  in this form is a cartridge heater, however, it should be understood that the teachings of the present disclosure may be applied to other types of heaters as set forth in greater detail below while remaining within the scope of the present disclosure. As shown, the heater  20  comprises a resistive heating element  22  having two end portions  24  and  26 , and the resistive heating element  22  is in the form of a metal wire, such as a nichrome material by way of example. The resistive heating element  22  is wound or disposed around a non-conductive portion (or core in this form)  28 . The core  28  defines a proximal end  30  and a distal end  32  and further defines first and second apertures  34  and  36  extending through at least the proximal end  30 . 
     The heater  20  further comprises a first power pin  40  that is made of a first conductive material and a second power pin  42  that is made of a second conductive material that is dissimilar from the first conductive material of the first power pin  40 . Further, the resistive heating element  22  is made of a material that is different from the first and second conductive materials of the first and second power pins  40 ,  42  and forms a first junction  50  at end  24  with the first power pin  40  and a second junction  52  at its other end  26  with the second power pin  42 . Because the resistive heating element  22  is a different material than the first power pin  40  at junction  50  and is a different material than the second power pin  42  at junction  52 , a thermocouple junction is effectively formed and thus changes in voltage at the first and second junctions  50 ,  52  are detected (as set forth in greater detail below) to determine an average temperature of the heater  20  without the use of a separate/discrete temperature sensor. 
     In one form, the resistive heating element  22  is a nichrome material, the first power pin  40  is a Chromel® nickel alloy, and the second power pin  42  is an Alumel® nickel alloy. Alternately, the first power pin  40  could be iron, and the second power  42  could be constantan. It should be appreciated by those skilled in the art that any number of different materials and their combinations can be used for the resistive heating element  22 , the first power pin  40 , and the second power pin  42 , as long as the three materials are different and a thermocouple junction is effectively formed at junctions  50  and  52 . The materials described herein are merely exemplary and thus should not be construed as limiting the scope of the present disclosure. 
     In one application, the average temperature of the heater  20  may be used to detect the presence of moisture. If moisture is detected, moisture management control algorithms can then be implemented via a controller (described in greater detail below) in order to remove the moisture in a controlled manner rather than continuing to operate the heater  20  and a possible premature failure. 
     As further shown, the heater  20  includes a sheath  60  surrounding the non-conductive portion  28  and a sealing member  62  disposed at the proximal end  30  of the non-conductive portion  28  and extending at least partially into the sheath  60  to complete the heater assembly. Additionally, a dielectric fill material  64  is disposed between the resistive heating element  22  and the sheath  60 . Various constructions and further structural and electrical details of cartridge heaters are set forth in greater detail in U.S. Pat. Nos. 2,831,951 and 3,970,822, which are commonly assigned with the present application and the contents of which are incorporated herein by reference in their entirety. Therefore, it should be understood that the form illustrated herein is merely exemplary and should not be construed as limiting the scope of the present disclosure. 
     Referring now to  FIG.  2   , the present disclosure further includes a controller  70  in communication with the power pins  40 ,  42  and configured to measure changes in voltage at the first and second junctions  50 ,  52 . More specifically, the controller  70  measures millivolt (mV) changes at the junctions  50 ,  52  and then uses these changes in voltage to calculate an average temperature of the heater  20 . In one form, the controller  70  measures changes in voltage at the junctions  50 ,  52  without interrupting power to the resistive heating element  22 . This may be accomplished, for example, by taking a reading at the zero crossing of an AC input power signal. In another form, power is interrupted and the controller  70  switches from a heating mode to a measuring mode to measure the changes in voltage. Once the average temperature is determined, the controller  70  switches back to the heating mode, which is described in greater detail below. More specifically, in one form, a triac is used to switch AC power to the heater  20 , and temperature information is gathered at or near the zero-cross of the power signal. Other forms of AC switching devices may be employed while remaining within the scope of the present disclosure, and thus the use of a triac is merely exemplary and should not be construed as limiting the scope of the present disclosure. 
     Alternately, as shown in  FIG.  3   , a FET  72  is used as a switching device and means of measuring voltage during an off-period of the FET with a DC power supply. In one form, three (3) relatively large resistors  73 ,  74 , and  75  are used to form a protective circuit for the measurement circuit  76 . It should be understood that this switching and measurement circuit is merely exemplary and should not be construed as limiting the scope of the present disclosure. 
     Referring back to  FIG.  2   , a pair of lead wires  80  are connected to the first power pin  40  and the second power pin  42 . In one form, the lead wires  80  are both the same material such as, by way of example, copper. The lead wires  80  are provided to reduce the length of power pins needed to reach the controller  70 , while introducing another junction by virtue of the different materials at junctions  82  and  84 . In this form, in order for the controller  70  to determine which junction is being measured for changes in voltage, signal wires  86  and  88  may be employed such that the controller  70  switches between the signal wires  86  and  88  to identify the junction being measured. Alternately, the signal wires  86  and  88  may be eliminated and the change in voltage across the lead wire junctions  82  and  84  can be negligible or compensated through software in the controller  70 . 
     Referring now to  FIG.  4   , the teachings of the present disclosure may also be applied to a heater  20 ′ having a plurality of zones  90 ,  92  and  94 . Each of the zones includes its own set of power pins  40 ′,  42 ′ and resistive heating element  22 ′ as described above (only one zone  90  is illustrated for purposes of clarity). In one form of this multi-zone heater  20 ′, the controller  70  (not shown) would be in communication with the end portions  96 ,  98 , and  100  of each of the zones in order to detect voltage changes and thus determine an average temperature for that specific zone. Alternately, the controller  70  could be in communication with only the end portion  96  to determine the average temperature of the heater  20 ′ and whether or not moisture may be present as set forth above. Although three (3) zones are shown, it should be understood that any number of zones may be employed while remaining within the scope of the present disclosure. 
     Turning now to  FIG.  5   , the teachings of the present disclosure may also be applied to a plurality of separate heaters  100 ,  102 ,  104 ,  106 , and  108 , which may be cartridge heaters, and which are connected in sequence as shown. Each heater comprises first and second junctions of the dissimilar power pins to the resistive heating element as shown and thus the average temperature of each heater  100 ,  102 ,  104 ,  106 , and  108  can be determined by a controller  70  as set forth above. In another form, each of the heaters  100 ,  102 ,  104 ,  106 , and  108  has its own power supply pin and a single power return pin is connected to all of the heaters in order to reduce the complexity of this multiple heater form. In this form with cartridge heaters, each core would include passageways to accommodate power supply pins for each successive heater. 
     Referring now to  FIGS.  6  and  7   , a pitch of the resistive heating element  110  may be varied in accordance with another form of the present disclosure in order to provide a tailored heat profile along the heater  120 . In one form ( FIG.  5   ), the resistive heating element  110  defines a continuously variable pitch along its length. More specifically, the resistive heating element  110  has a continuously variable pitch with the ability to accommodate an increasing or decreasing pitch P 4 -P 9  on the immediately adjacent next 360 degree coil loop. The continuously variable pitch of resistive heating element  110  provides gradual changes in the flux density of a heater surface (e.g., the surface of a sheath  112 ). Although the principle of this continuously variable pitch is shown as applied to a tubular heater having filled insulation  114 , the principles may also be applied to any type of heater, including without limitation, the cartridge heater as set forth above. Additionally, as set forth above, the first power pin  122  is made of a first conductive material, the second power pin  124  is made of a second conductive material that is dissimilar from the first conductive material of the first power pin  122 , while the resistive heating element  110  is made of a material that is different from the first and second conductive materials of the first and second power pins  122 ,  124  so that changes in voltage at the first and second junctions  126 ,  128  are detected to determine an average temperature of the heater  120 . 
     In another form ( FIG.  7   ), the resistive heating element  130  has pitches P 1 , P 2 , and P 3  in zones A, B, and C, respectively. P3 is greater than P1, and P1 is greater than P2. The resistive heating element  130  has a constant pitch along the length of each zone as shown. Similarly, the first power pin  132  is made of a first conductive material, the second power pin  134  is made of a second conductive material that is dissimilar from the first conductive material of the first power pin  132 , while the resistive heating element  130  is made of a material that is different from the first and second conductive materials of the first and second power pins  132 ,  134  so that changes in voltage at the first and second junctions  136 ,  138  are detected to determine an average temperature of the heater  120 . 
     Referring to  FIG.  8   , the heater and dual purpose power pins as described herein have numerous applications, including by way of example a heat exchanger  140 . The heat exchanger  140  may include one or a plurality of heating elements  142 , and each of the heating elements  142  may further include zones or variable pitch resistive heating elements as illustrated and described above while remaining within the scope of the present disclosure. It should be understood that the application of a heat exchanger is merely exemplary and that the teachings of the present disclosure may be employed in any application in which heat is being provided while also requiring a temperature measurement, whether that temperature be absolute or for another environmental condition such as the presence of moisture as set forth above. 
     As shown in  FIG.  9   , the teachings of the present disclosure may also be applied to other types of heaters such as a layered heater  150 . Generally, the layered heater  150  includes a dielectric layer  152  that is applied to a substrate  154 , a resistive heating layer  156  applied to the dielectric layer  152 , and a protective layer  158  applied over the resistive heating layer  156 . A junction  160  is formed between one end of a trace the resistive layer  158  and a first lead wire  162  (only one end is shown for purposes of clarity), and similarly a second junction is formed at another end, and following the principles of the present disclosure as set forth above, voltage changes at these junctions are detected in order to determine the average temperature of the heater  150 . Such layered heaters are illustrated and described in greater detail in U.S. Pat. No. 8,680,443, which is commonly assigned with the present application and the contents of which are incorporated herein by reference in their entirety. 
     Other types of heaters rather than, or in addition to the cartridge, tubular, and layered heaters as set forth above may also be employed according to the teachings of the present disclosure. These additional types of heaters may include, by way of example, a polymer heater, a flexible heater, heat trace, and a ceramic heater. It should be understood that these types of heaters are merely exemplary and should not be construed as limiting the scope of the present disclosure. 
     Referring now to  FIG.  10   , a method of controlling at least one heater in accordance with the teachings of the present disclosure is shown. The method comprises the steps of: 
     (A) activating a heating mode to supply power to a power supply pin, the power supply pin made of a first conductive material, and to return the power through a power return pin, the power return pin made of a conductive material that is dissimilar from the first conductive material; 
     (B) supplying power to the power supply pin, to a resistive heating element having two ends and made of a material that is different from the first and second conductive materials of the power supply and return pins, the resistive heating element forming a first junction at one end with the power supply pin and a second junction at its other end with the power return pin, and further supplying the power through the power return pin; 
     (C) measuring changes in voltage at the first and second junctions to determine an average temperature of the heater; 
     (D) adjusting the power supplied to the heater as needed based on the average temperature determined in step (C); and 
     (E) repeating steps (A) through (D). 
     In another form of this method, as shown by the dashed lines, step (B) is interrupted while the controller switches to a measuring mode to measure the change in voltage, and then the controller is switched back to the heating mode. 
     Yet another form of the present disclosure is shown in  FIGS.  11 - 13   , wherein a heater for use in fluid immersion heating is illustrated and generally indicated by reference numeral  200 . The heater  200  comprises a heating portion  202  configured for immersion into a fluid, the heating portion  202  comprising a plurality of resistive heating elements  204 , and at least two non-heating portions  206 ,  208  contiguous with the heating portion  202  (only one non-heating portion  206  is shown in  FIG.  11   ). Each non-heating portion  206 ,  208  defines a length and comprises a corresponding plurality of sets of power pins electrically connected to the plurality of heating elements  204 . More specifically, each set of power pins comprises a first power pin  212  made of a first conductive material and a second power pin  214  made of a second conductive material that is dissimilar from the first conductive material of the first power pin  212 . The first power pins  212  are electrically connected to the second power pins  214  within the non-heating portions  206 ,  208  to form junctions  220 ,  230 , and  240 . As further shown, the second power pins  214  extend into the heating portion  202  and are electrically connected to the corresponding resistive heating elements  204 . Further, the second power pins  214  define a cross-sectional area that is larger than the corresponding resistive heating element  204  so as to not create another junction or measurable amount of heat at the connection between the second power pins  24  and the resistive heating elements  204 . 
     As further shown, a termination portion  250  is contiguous with the non-heating portion  206 , and the plurality of first power pins  212  exit the non-heating portion  206  and extend into the termination portions  250  for electrical connection to lead wires and a controller (not shown). Similar to the previous description, each of the resistive heating elements  204  are made of a material that is different from the first and second conductive materials of the first and second power pins  212 ,  214 , and wherein each of the junctions  220 ,  230 , and  240  of the first power pin  212  to the second power pin  214  is disposed at a different location along the lengths of the non-heating portions  206 ,  208 . More specifically, and by way of example, junction  220  is at a distance L 1 , junction  230  is at a distance L 2 , and junction  240  is at a distance L 3 . 
     As shown in  FIG.  13   , with temperature of the junctions  220 ,  230 , and  240  over time “t,” the junction  220  is submerged in the fluid F, the junction  230  is submerged but not as deep in the fluid, and the junction  240  is not submerged. Accordingly, detecting changes in voltage at each of the junctions  220 ,  230 , and  240  can provide an indication of the fluid level relative to the heating portion  202 . It is desirable, especially when the fluid is oil in a cooking/fryer application, that the heating portion  202  not be exposed to air during operation so as to not cause a fire. With the junctions  220 ,  230 , and  240  according to the teachings of the present disclosure, a controller can determine if the fluid level is too close to the heating portion  202  and thus disconnect power from the heater  200 . 
     Although three (3) junctions  220 ,  230 , and  240  are illustrated in this example, it should be understood that any number of junctions may be employed while remaining within the scope of the present disclosure, provided that the junctions are not in the heating portion  202 . 
     Referring now to  FIG.  14   , yet another form of the present disclosure includes a plurality of heater cores  300  arranged in zones of a heater system  270  as shown. The heater cores  300  in this exemplary form are cartridge heaters as described above, however, it should be understood that other types of heaters as set forth herein may also be employed. Accordingly, the cartridge heater construction in this form of the present disclosure should not be construed as limiting the scope of the present disclosure. 
     Each heater core  300  includes a plurality of power pins  301 ,  302 ,  303 ,  304 , and  305  as shown. Similar to the forms described above, the power pins are made of different conductive materials, and more specifically, power pins  301 ,  304 , and  305  are made of a first conductive material, power pins  302 ,  303 , and  306  are made of a second conductive material that is dissimilar from the first conductive material. As further shown, at least one jumper  320  is connected between dissimilar power pins, and in this example, power pin  301  and power pin  303 , in order to obtain a temperature reading proximate the location of the jumper  320 . The jumper  320  may be, for example, a lead wire or other conductive member sufficient to obtain the millivolt signal indicative of temperature proximate the location of the jumper  320 , which is also in communication with the controller  70  as illustrated and described above. Any number of jumpers  320  may be used across dissimilar power pins, and another location is illustrated at jumper  322  between power pin  303  and power pin  305 , between ZONE  3  and ZONE  4 . 
     In this exemplary form, power pins  301 ,  303 , and  305  are neutral legs of heater circuits between adjacent power pins  302 ,  304 , and  306 , respectively. More specifically, a heater circuit in ZONE  1  would be between power pins  301  and  302 , with the resistive heating element (e.g., element  22  shown in  FIG.  1   ) between these power pins. A heater circuit in ZONE  2  would be between power pins  303  and  304 , with the resistive heating element between these two power pins. Similarly, a heater circuit in ZONE  3  would be between power pins  305  and  306 , with the resistive heating element between these two power pins. It should be understood that these heater circuits are merely exemplary and are constructed according to the teachings of a cartridge heater described above and with reference to  FIG.  1   . Any number and configurations of heater circuits with multiple heater cores  300  and zones may be employed while remaining within the scope of the present disclosure. The illustration of four (4) zones and a cartridge heater construction is merely exemplary and it should be understood that the dissimilar power pins and jumpers may be employed with other types of heaters and in a different number and/or configuration of zones while remaining within the scope of the present disclosure. 
     Referring now to  FIG.  15   , in one form, a heater  400  is configured to include a primary sensing junction that can be arranged within the heater  400  or outside the heater  400  for measuring temperature. The heater  400  includes a resistive heating element  402 , a first power pin  404 , and a second power pin  406 . The resistive heating element  402  has a first end and a second end. The first power pin  402  is connected to the first end of the resistive heating element  402  to form a first junction  408 , and the second power pin  406  is connected to the second end of the resistive heating element  402  to form a second junction  410 . The first power pin  404  and the second power pin  406  are operable to supply power to the heating element  402  by way of the controller. 
     The second power pin  406  includes a first lead wire  412  and a second lead wire  414 . The first lead wire  412  is connected to the second end of the resistive heating element  402  to form the second junction  410 , and the second lead wire  414  is connected to the first lead wire  412  to form a primary sensing junction  416  at a first reference area. The second lead wire  414  is configured to connect the resistive heating element  402  to the controller by way of the first lead wire  412 . 
     In one form, the first lead wire  412  and the second lead wire  414  are made of dissimilar conductive materials or more particularly, materials having different Seebeck coefficients. For example, various combinations of nickel alloys, iron, constantan, Alumel® or the like may be used. The difference in material of the first lead wire  412  and the second lead wires  414  is represented by the different style lines in  FIG.  15    (e.g., dash line for the second lead wire  414  and dashed-dotted line for first lead wire  412 ). Since the materials are different, the primary sensing junction  416  is effectively a thermocouple to generate a voltage change that is measured to determine a temperature at the first reference area. Accordingly, in this form, the junctions  408  and  410  for connecting to the resistive heating element  402  is separated from a sensing location. Thus, the heater  400  is not restricted to detecting temperature at the ends of the heating element  402 , and a temperature measurement may be detected at various locations within the heater  400 . Furthermore, in one form, the first lead wire  412  and the second lead wire  414  are configured to have the primary sensing junction  416  outside of the heater  400 . 
     As discussed with respect to  FIG.  2   , the controller (not shown in  FIG.  15   ) is in communication with the first power pin  404  and the second power pin  406  and is configured to supply power to the resistive heater element  402  via the power pins  404  and  406 . The controller is also configured to calculate the temperature at the first reference area based on the voltage change created by the sensing junction  416  using the Seebeck coefficients of the materials. 
     In one form, the resistive heating element  402 , the first power pin  404 , and the first lead wire  412  of the second power pin  406  are made of the same conductive material or of materials with similar Seebeck properties (i.e., substantially the same Seebeck coefficients). Accordingly, a voltage change created by the first junction  408  and the second junction  410  is substantially zero, and the temperature measurement determined by the controller is based on the voltage change created by the primary sensing junction  416 . 
     In another form, the resistive heating element  402 , the first power pin  404 , and/or the first lead wire  412  of the second power pin  406  are made of different conductive materials. With such configurations, the material of the second lead wire  414  is selected such that the Seebeck coefficient of the second lead wire  414  is the most dissimilar from that of the resistive heating element  402 , the first power pin  404 , and the first lead wire  412  of the second power pin  406 . Accordingly, the primary sensing junction  416  is provided as the largest contributor to overall temperature measurement, and any temperature measurement from the first and second junctions  408  and  410  are minimized. 
     As discussed above, the temperature can be detected at the zero-crossing of the power signal. Alternatively, the controller is configured to switch between a heating mode for directing power to the resistive heating element and a measuring mode for measuring changes in voltage at the primary sensing junction  416  to determine the temperature at the reference area. 
     Referring to  FIG.  16   , in one form, a heater  420  includes two sensing junctions in proximity to each other to detect a temperature at a virtual point between the two sensing junctions. Here, the heater  420  comprises a resistive heating element  422 , a second power pin  424 , and a first power pin  426 . The resistive heating element  422  comprises a first end and a second end. The first power pin  426  forms a first junction  428  with the first end of the heating element  422 , and the second power pin  424  forms a second junction  430  with the second end of the heating element  422 . The second power pin  424  is configured in a similar manner as the second power pin  406  of  FIG.  15   , and thus, includes a first lead wire  432  that is connected to the resistive heating element  422  to form the second junction  430 , and a second lead wire  434  that is connected to the first lead wire  432  to form a first primary sensing junction  440  at a first reference area within the heater  420 . 
     In this form, the first power pin  426  is configured in a similar manner as the second power pin  424 , and comprises two lead wires (i.e., a third lead wire  436  and a fourth lead wire  438 ) to form a sensing junction. More particularly, the third lead wire  436  is connected to the first end of the resistive heating element  422  to form the first junction  428 , and the fourth lead wire  438  forms a second primary sensing junction  442  with the third lead wire  436  at a second reference area. The second primary sensing junction  442  is provided at a second reference area of the heater  420  that is adjacent and proximate to the first reference area having the first primary sensing junction  440 . While the sensing junctions  440  and  442  are provided as within the heater  420 , the sensing junctions  440  and  442  can also be provided outside the heater  420 . 
     Similar to the second power pin  424 , the third lead wire  436  is made of a different conductive material than that of the fourth lead wire  438 , and is of different conductive material as that of the second lead wire  434  of the second power pin  424 . Accordingly, the second primary sensing junction  442  is effectively a thermocouple used in conjunction with the first primary sensing junction to determine a temperature between the first and second reference areas. Furthermore, the resistive heating element  422 , the first lead wire  432  of the second power pin  424 , and the third lead wire  436  of the first power pin  426  are made of the same conductive material or of materials with similar Seebeck properties, such that a voltage change created by the first junction  428  and the second junction  430  is substantially zero, and the temperature measurement determined by the controller is based on the voltage changes at the sensing junctions  440  and  442 . 
     The controller (not shown in  FIG.  16   ) is configured to supply power to the heating element  422  via the first power pin  426  and the second power pin  424 , and to measure a temperature at a virtual point between the two sensing junctions  440  and  442  based on the voltage changes created by the junctions  440  and  442 . In one form, the temperature at the first and second reference areas are presumed to be substantially the same, and thus, the temperature detected by the controller is associated with a virtual point between the first and second reference areas. 
     Referring to  FIG.  17 A  and  FIG.  17 B , in one form, the primary sensing junction is provided in a cartridge heater for measuring a temperature at a virtual point outside of the heater or at a reference area within the heater.  FIG.  17 A  illustrates a cartridge heater  450  that includes a resistive heating element  452  in the form of a metal wire, a first power pin  454 , and a second power pin  456 . The cartridge heater  450  is configured to include two sensing junctions provided outside of the heater  450  to measure a temperature at a virtual point between the two sensing junctions. 
     More particularly, in one form, the resistive heating element  452  is wound or disposed around a non-conductive portion (or a core in this form) as discussed with respect to  FIG.  1   . The first power pin  454  comprises a first lead wire  458  and a second lead wire  460 . The first lead wire  458  is connected to the first end of the resistive heating element  452  to form a first junction  462 , and the second lead wire  460  forms a first primary sensing junction  464  with the first lead wire  458  at a first reference area outside the heater  450 . The second power pin  456  comprises a third lead wire  466  and a fourth lead wire  468 . The third lead wire  466  is connected to the resistive heating element  452  to form a second junction  470 . The fourth lead wire  468  is connected to the third lead wire  466  to form a second primary sensing junction  472  at a second reference area outside the heater  450 . The first and second primary sensing junctions  464  and  472  are positioned adjacent and in proximity to one another. 
     In one form, the resistive heating element  452 , the first lead wire  458  of the first power pin  454 , and the third lead wire  466  of the second power pin  456  are made of the same material or of materials having similar Seebeck properties, and are different from the material of the second lead wire  460  of the first power pin  454  and the fourth lead wire  468  of the second power pin  456 . In addition, the material of the second lead wire  460  of the first power pin  454  is different from the material of the fourth lead wire  468  of the second power pin  456 . Accordingly, the first and second primary junctions  464  and  472  operate as thermocouples to detect a temperature at a virtual point between the two junctions  464  and  472 . 
       FIG.  17 B  illustrates a cartridge heater  480  having one primary sensing junction located within the heater. The cartridge heater  480  includes a resistive heating element  482  having two ends, a first power pin  484 , and a second power pin  486 . The first power pin  484  forms a first junction  488  with a first end of the heating element  482  and the second power pin  486  forms a second junction  490  with a second end of the heating element  482 . Similar to the heater of  FIG.  15   , the second power pin  486  includes a first lead wire  492  and a second lead wire  494 , which are made of different material (i.e., have different Seebeck coefficients). The first lead wire  492  is connected to the second end of the resistive heating element  482  to form the second junction  490 , and the second lead wire  494  is connected to the first lead wire  492  to form a primary sensing junction  496  at a first reference area within the heater  480 . Accordingly, the primary sensing junction  490  is operable as a thermocouple to measure a temperature at the first reference area. 
     In one form, the resistive heating element  482 , the first power pin  484 , and the first lead wire  492  of the second power pin  486  are made of the same conductive material or of materials having similar Seebeck properties. Accordingly, a voltage change created by the first junction  488  and the second junction  490  is substantially zero, and the temperature measurement determined by the controller is based on the voltage change created by the primary sensing junction  490 . 
     Referring to  FIG.  18   , the primary sensing junction of the present disclosure may also be used as part of a heat flux sensor to estimate a temperature between inner surface of a heater and an outer surface of the heater. More particularly, in one form, a heater  500  is operable to heat a fluid (e.g., a gas) following through a tube, and comprises a resistive heating (i.e., thermal) element  502  (shown with phantom lines), a first power pin  504 , and a second power pin  506 . While not fully illustrated in  FIG.  18   , the resistive heating element  502  is configured to extend through the heater  500 , and is protected by a cover. The first power pin  504  and the second power pin  506  extend into the cover of the heater  500  to form a first junction with a first end of the heating element  502  and a second junction with a second end of the heating element  502 , respectively. 
     The resistive heating element  502  is a “two-wire” heating element such that it functions as a heater and as a temperature sensor. Such two-wire capability is disclosed in, for example, U.S. Pat. No. 7,196,295, which is commonly assigned with the present application and incorporated herein by reference in its entirety. Generally, for a two-wire system, the heating element  502  is made of a high temperature coefficient of resistance (TCR) material. A controller (not shown in  FIG.  18   ) is in communication with the first and second power pins  504  and  506 , and configured to measure voltage (i.e., mV) changes across the power pins  504  and  506 . Using the voltage change, the controller calculates an average temperature of the resistive heating element  502  (e.g., about R1). 
     The first power pin  504  includes a first lead wire  508  and a second lead wire  510 , which are made of different materials (i.e., have different Seebeck coefficients). The first lead wire  508  forms the second junction with the heating element  502 , and the second lead wire  510  forms a primary sensing junction  512  with the first lead wire  508  at a second reference area that is along an outer surface (i.e., R2) of the heater  500  (i.e., along a plane that is different than that of the heating element  502 ). Accordingly, the primary sensing junction  512  is operable as a thermocouple to measure a temperature at the second reference area based on a voltage change created by the sensing junction  512 . The resistive heating element  502 , the second power pin  506 , and the first lead wire  508  of the first power pin  504  are made of the same material or made of materials having similar Seebeck properties. 
     In one form, the controller is configured to estimate a temperature at a virtual point between an inner surface (i.e., first reference area) and an outer surface (a second reference area) of the heater  500  based on the temperature measurement of the heating element  502 , the temperature at the primary sensing junction  512 , and power delivered to the heater  500  from the controller. More particularly, the controller determines the average temperature of the heating element at the first reference area using the voltage change across the power pins  506  and  504 , as described with respect to the two-wire system. The controller further determines the temperature at the second reference area based on the voltage change created by the primary sensing junction  512  and the Seebeck coefficient of the first and second lead wire  508  and  510 . Using the two measurements, the power being provided, and the heater geometry, the controller may calculate a temperature at a third reference area at a desired location in the heater  500  (e.g., any location within the heater). In addition, if the geometry of the heater  500  is known, the controller can also be configured to determine a heat flux between the inner surface and the outer surface of the heater  500 . The heat flux can be used to, for example, detect entry areas of cold fluid, adjust temperature set-points, and/or other suitable system controls. While the heater  500  is illustrated as a tube, the heater may be configured in other suitable shapes (e.g., a flat plate) and still be within the scope of the present disclosure. 
     Furthermore, in one form, before the heater  500  is energized, the heater  500  is substantially at room temperature, such that the primary sensing junction  512  is at the same or substantially the same temperature as the high TCR element wire (i.e., the heating element  502 ). The controller is configured to measure the temperature using the primary sensing junction  512 , and further measure the resistance of the heating element  502 . The controller associates the resistance of the heater  500  with the temperature measured by the primary sensing junction  512 , and uses this baseline value to covert other resistances to a temperature, thereby calibrating the heater element  502 . 
     Referring to  FIG.  19   , a primary sensing junction can be configured in various suitable ways to improve temperature measurement along a surface. For example, in one form, a primary sensing junction  550  is formed by a first lead wire  552  and a second lead wire  554  that are made of different materials. The sensing junction  550  has a planar shape (i.e., flat) and is surrounded by a heat diffuser  556  that is a thermally conductive material (e.g., copper) to improve thermal contact with the surface and to diffuse heat coming from the heating element. 
     The primary sensing junction of the present disclosure operates as a thermocouple to enables temperature measurements at different locations within and even, outside of the heater. Accordingly, temperature measurement is not restricted to the ends of the heating element. In addition, the heater no longer requires a discrete temperature sensor, thereby reducing the complexity of the heater. 
     Referring to  FIG.  20   , a heater system  700  including a power control system  600  and a plurality of heaters  602 ,  604 ,  606 ,  608  connected and controlled by the power control system  600  is shown. The power control system  600  includes a controller  610 , a wire harness  612 , and a plurality sets of auxiliary wires  632 ,  634 ,  636  connected to and extending from the plurality of heaters. The wire harness  612  and the plurality sets of auxiliary wires  632 ,  634 ,  636  connect the controller  610  to the plurality of heaters  602 ,  604 ,  606 ,  608 . The plurality of heaters include a first heater  602 , a second heater  604 , a third heater  606 , and a fourth heater  608 . The wire harness  612  may be used to connect some or all of the plurality of heaters  602 ,  604 ,  606 , and  608  in series to form different modular heater assemblies or as stand-alone heaters, or a combination thereof, which will be described in more detail below. Any number of heaters may be connected by the wire harness  612 , and the heaters may be any type of heaters without departing from the scope of the present disclosure. The controller  610  is configured to supply power to the plurality of heaters  602 ,  604 ,  606 ,  608 , determine temperatures of the plurality of heaters  602 ,  604 ,  606 ,  608  based on temperature signals transmitted from the heaters, and control the temperatures of the plurality of heaters  602 ,  604 ,  606 ,  608  based on the measured temperatures and target temperatures. 
     The wire harness  612  includes a plurality of connectors  614 ,  616 ,  618 ,  620  and a plurality of electrical wires for connecting the controller  610  to the plurality of heaters  602 ,  604 ,  606 ,  608 . In one form, the plurality of connectors  614 ,  616 ,  618 ,  620  may be circular plastic connectors (CPC), which include built-in pins and sockets to allow for a wide range of power and signal transmission options, and which are structurally designed to allow for easy and quick connect/disconnect between the connectors and the electrical wires. In the illustrative example of  FIG.  20   , the number of the plurality of connectors  614 ,  616 ,  618 ,  620  is equal to the number of the plurality of heaters  602 ,  604 ,  606 ,  608  such that each of the heaters is connected to another heater(s) or the controller  610  via a corresponding connector. 
     In the illustrative example of  FIG.  20   , the plurality of electrical wires include a main power supply wire  622 , a main power return wire  624 , and a plurality of connecting wires  626 ,  628 ,  630 . The main power supply wire  622  and the main power return wire  624  are directly connected to the controller  610  for routing electric current to and out of the plurality of heaters  602 ,  604 ,  606 ,  608 , respectively. The plurality of connecting wires include a first connecting wire  426 , a second connecting wire  428 , and a third connecting wire  430  for connecting one of the connectors  614 ,  616 ,  618 ,  620  to another one of the connectors  614 ,  616 ,  618 ,  620 . The plurality sets of auxiliary wires are disposed between the connectors  614 ,  616 ,  618 ,  620  and the plurality of heaters  602 ,  604 ,  606 ,  608 . It should be understood that three (3) connecting wires and four (4) heaters are merely exemplary and the illustrations and descriptions herein should not be construed as limiting the scope of the present disclosure. It is also understood that the plurality sets of auxiliary wires may be alternatively configured to be in the form of conductive pins without departing from the scope of the present disclosure. 
     Referring to  FIG.  21 A , each set of auxiliary wires fora corresponding heater includes three wires, wherein two of the three wires are made of different materials and are joined to form a thermocouple junction  635 , which is also joined to an end of a resistive heating element  637  of the heater  602 . More specifically, each set of auxiliary wires includes a temperature sensing wire  432 , an auxiliary power supply wire  634 , and an auxiliary power return wire  636 . The temperature sensing wire  632  is made of a first conductive material (as shown in dashed line), whereas the auxiliary power supply wire  634  and the auxiliary power return wire  634  are made of a second conductive material (as shown in solid lines) different from the first conductive material. 
     The temperature sensing wire  632  (made of the first conductive material) is joined to one of the auxiliary power supply wire  634  and the auxiliary power return wire  634  (made of the second conductive material) to form a thermocouple junction  635  therebetween. As shown in  FIG.  21 A , the temperature sensing wire  632  of each set of auxiliary wires is joined to the auxiliary power supply wire  634  and joined to one of a pair of terminal areas of a resistive heating element  637  to form a thermocouple junction  635  therebetween. The auxiliary power return wire  636  is connected to the other one of the terminal areas of the resistive heating element  637 . As such, electric current flows from the temperature sensing wire  632 , through the resistive heating element  637 , to the auxiliary power return wire  636 . The three wires may be fixed to the terminal areas of a resistive heating element  637  of a heater to become a part of the heater. 
     While three wires extend from each heater and are connected to the corresponding connector, only two of the three wires are used to carry electric current and the remaining one of the three wires is bypassed during each mode of heater operation. Which one of the three wires is bypassed depends on how the heaters are connected by the wire harness, particularly by the connectors  614 ,  616 ,  618 ,  620  each including a first connector part and a second connector part. For example, as shown in  FIG.  21 A , the connector  614  includes a first connector part  614   a  and a second connector part  614   b . All three wires are connected to a first connector part of a specific connector, but the second connector part of the specific connector connects only two of the three wires to a second connector part of another connector or the controller  610  via connecting wire(s), the main power supply wire, or the main power return wire. As shown in  FIG.  21 A  in conjunction with  FIG.  20   , the temperature sensing wire  632  and the auxiliary power return wire  636  for the first heater  602  are used to carry electric current and the auxiliary power supply wire  634  is bypassed. As clearly shown in  FIG.  20   , the auxiliary power supply wires  634  and the auxiliary power return wires  636  for the other heaters  604 ,  606 ,  608  are used to carry electric current and the temperature sensing wires  632  are bypassed. The thermocouple junction  635  on the first heater  602  measures the temperature of the first heater, and the temperature sensing wire  632  and the auxiliary power return wire  636  for the first heater  602  transmit a signal relating to the temperature of the heater to the controller  610 . 
     As an example, the first conductive material may be a copper-nickel alloy such as Constantan, and the second conductive material may be a nickel-chromium alloy such as Chromel®. Any combination of first and second conductive materials suitable for forming a thermocouple junction for temperature sensing purposes may be used without departing from the scope of the present disclosure. 
     Referring to  FIG.  21 B , each of the connectors  614 ,  616 ,  618 ,  620  may include a first connector part and a mating second connector part (which may be a socket and plug assembly, for example). For example, the connector  614  may include a first connector part  614   a  and a second connector part  614   b . The heater  602  and the corresponding set of auxiliary wires (i.e., the temperature sensing wire  632 , the auxiliary power supply wire  634 , and the auxiliary power return wire  636 ) are attached to the first connector part  614   a  to form a modular heater unit  603 . The modular heater unit  603  can be easily connected to other electrical components, such as another modular heater unit or the controller  610 , by using mating connector parts and proper connecting wires to achieve various wiring connections, all variations of which should be construed as falling within the scope of the present disclosure. 
     The set of auxiliary wires extending from the corresponding heater constitutes a three-wire mechanism to allow the heater to be used as both a heater and a temperature sensor. In the first modular heater assembly of  FIG.  20   , the second, third and fourth heaters  604 ,  606 ,  608  are connected by the wire harness  612  in a way such that the second, third and fourth heaters are used as heaters only to generate a desired heat output. In the second, third and fourth heaters  604 ,  606 ,  608 , the auxiliary power supply wires  634  and the auxiliary power return wires  636  are selectively used to form a part of the electric circuit, whereas the temperature sensing wires  632  are bypassed. The first heater  602  is used as both a heater and a temperature sensor by selectively using the temperature sensing wire  632  and the auxiliary power supply wire  634  to form a part of the electric circuit, and by bypassing the auxiliary power supply wire  634 . During the temperature sensing mode, the thermocouple junction  635  on the first heater  602  is used to measure a temperature of the heater, and the temperature sensing wire  632  and the auxiliary power return wire  636  for the first heater and other wires in the electric circuit are used to transmit a temperature signal to the controller  610 . 
     Referring to  FIG.  22   , an electric diagram illustrating the electric circuit of the heater system  700  including the power control system  600  and the plurality of heaters of  FIG.  20    is shown. The plurality of heaters  602 ,  604 ,  606 , and  608  are connected in series in this order to form a first modular heater assembly. The main power supply wire  622  is made of the same first conductive material of the temperature sensing wires  632  as shown in dashed line. The main power return wire  624  and the connecting wires  626 ,  628 ,  630  are made of the same second conductive material of the auxiliary power supply wire  634  and the auxiliary power return wire  636  as shown in solid lines. As an example, the first conductive material may be Constantan, and the second conductive material may be Chromel®. 
     When the control system  600  is in the power mode, the power is supplied from CH2+ of the controller  610  through the main power supply wire  622 , the temperature sensing wire  632  and the auxiliary power return wire  636  of the first heater  602 , the connecting wire  626 , the auxiliary power supply wire  634  and the auxiliary power return wire  636  of the second heater  604 , the connecting wire  628 , the auxiliary power supply wire  634  and the auxiliary power return wire  636  of the third heater  606 , the connecting wire  630 , the auxiliary power supply wire  634  and the auxiliary power return wire  636  of the fourth heater  608 . The electric current returns to CH2- of the controller  610  through the main power return wire  624 . 
     When the control system  600  is in the temperature sensing mode, the electric current path is the same as that in the power supply mode. The thermocouple junction  635  of the first heater  602  is used to measure a temperature of the first heater  602 . The temperature of the first heater  602  is also the temperature of the first modular heater assembly because the first, second, third and fourth heater are connected in series. The signal relating to the temperature measurement is transmitted to the controller  610  via the temperature sensing wire  632  and the auxiliary power return wire  636  of the first heater  602  and the other wires forming the circuit. 
     Only one of the thermocouple junctions  635  in the first modular heater assembly is used for temperature sensing. In the first modular heater assembly, the thermocouple junction  635  in the first heater  602  that is directly connected to the controller  610  by the main power supply wire  622  is used for temperature sensing. The main power supply wire  622  is made of the same first conductive material of the temperature sensing wire  632  and may be considered an extension of the temperature sensing wire in the first modular heater assembly. 
     Referring to  FIG.  23   , a heater system  702  including a power control system  600  and a plurality of heaters  602 ,  604 ,  606 ,  608  connected and controlled by the power control system  600  is shown. The power control system  600  includes a wire harness  612 ′, which routes the plurality of heaters  602 ,  604 ,  606 ,  608  in a second series connection. In the following, like elements will be designated by like reference numerals and the description thereof will be omitted for clarify. 
     In this wiring connection, the second heater  604 , the first heater  602 , the third heater  606 , and the fourth heater  608  are connected in series in this order to form a second modular heater assembly and the power is supplied to the second heater  604  first. In this wiring connection, only the second heater  604  is used as both a heater and a temperature sensor by selectively using the temperature sensing wire  632  and the auxiliary power return wire  636  for the second heater to form a part of the electric circuit. The other heaters  602 ,  606 ,  608  are used to perform only the function of heaters by selectively using the auxiliary power supply wires  634  and the auxiliary power return wires  636  to form a part of the circuit and by bypassing the temperature sensing wires. Only the thermocouple junction  635  of the second heater  604  is used for temperature sensing of the second modular heater assembly. Like the first modular heater assembly of  FIG.  20   , the main power supply wire  622  and the temperature sensing wires  632  are made of the first conductive material (such as Constantan), and the remaining wires are made of the second conductive material (such as Chromel®). The main power supply wire  622  may be considered an extension of the temperature sensing wire  632  for the second heater  604  for temperature sensing purposes. 
     Referring to  FIG.  24   , a heater system  704  including a power control system  600  and a plurality of a heaters  602 ,  604 ,  606 ,  608  connected and controlled by the power control system  600  is shown. The power control system  600  includes a wire harness  612 ″, which routes the plurality of heaters  602 ,  604 ,  606  and  608  in a third series connection. In this wiring connection, the third heater  606 , the second heater  604 , the first heater  602 , and the fourth heater  608  are connected in series in this order to form a third modular heater assembly and the power is supplied to the third heater  606  first. In this wiring connection, only the third heater  606  is used to perform the function of both a heater and a temperature sensor and the thermocouple junction  635  of the third heater  606  is used for temperature sensing. The other heaters  602 ,  604 ,  608  are used as heaters only by bypassing the temperature sensing wires  632  associated with these heaters. Similarly, the main power supply wire  622  and the temperature sensing wires  632  are made of the first conductive material (such as Constantan), and the remaining wires are made of the second conductive material (such as Chromel®). The main power supply wire  622  may be considered an extension of the temperature sensing wire  632  for the third heater  606  for temperature sensing purposes. 
     Referring to  FIGS.  25  and  26   , a heater system  706  including a power control system  600 ′ and a plurality of a heaters  602 ,  604 ,  606 ,  608  connected and controlled by the power control system  600  is shown. The power control system  600 ′ includes a wire harness  720 , which includes two sets of main power supply wires  622  and main power return wires  624  for routing one of the heaters (i.e., the fourth heater  608 ) as a stand-alone heater, and the remaining ones of the heaters (i.e., the first, second and third heaters  602 ,  604 ,  606 ) in a series connection. 
     The first set of main power supply and return wires connect the first heater  602 , the second heater  604 , the third heater  608  in series in this order to form a fourth modular heater assembly and the power is supplied from the controller  610  to the first heater  602  first. The second set of main power supply and return wires directly connect the fourth heater  608  to the controller  610  such that the fourth heater  408  becomes a stand-alone heater. The fourth heater  608  is controlled independently from the fourth modular heater assembly. 
     In this fourth modular heater assembly, only the first heater  602  is used as both a heater and a temperature sensor and the thermocouple junction  635  of the first heater  602  is used for temperature sensing. The fourth heater, which is a stand-alone heater, also functions as both a heater and a temperature sensor and the thermocouple junction  635  of the fourth heater is also used for measuring temperature of the fourth heater  608 . 
     Similarly, the two main power supply wires  622  and the temperature sensing wires  632  are made of the first conductive material (such as Constantan), and the remaining wires are made of the second conductive material (such as Chromel®). 
     Referring to  FIG.  27   , a heater system  708  including a power control system  600 ″ and a plurality of heaters  650 ,  652 ,  654 ,  656  connected and controlled by the power control system  600 ″ is shown. The power control system  600 ″ includes a plurality sets of auxiliary wires  632 ′,  634 ′,  636 ′,  660 ,  662  attached to the plurality of heaters  650 ,  652 ,  654 ,  656 , and a wire harness  722  for connecting the plurality sets of auxiliary wires to the controller  610 . The wire harness  722  includes two sets of main power supply wires  622  and main power return wires  624  for routing one of the heaters (e.g., the fourth heater  656 ) as a stand-alone heater, and the remaining ones of the heaters (i.e., the first, second and third heaters  650 ,  652 ,  654 ) in a series connection. The first heater  650 , the second heater  652 , and the third heater  654  are connected in series in this order to form a fifth modular heater assembly. 
     Each set of the auxiliary wires is attached to a corresponding heater and includes five wires, including a temperature sensing wire  632 ′, an auxiliary power supply wire  634 ′, an auxiliary power return wire  636 ′, a first routing wire  660 , and a second routing wire  662 . The structure and function of the temperature sensing wire  632 ′, the auxiliary power supply wire  634 ′ and the auxiliary power return wire  636 ′ are the same as that of the temperature sensing wire  632 , the auxiliary power supply wire  634 , and the auxiliary power return wire  636  and thus the detailed description thereof is omitted herein for clarity. The first routing wire  660  and the second routing wire  662  in each set are connected to each other and are used to help connect the first, second and third heater in a desired order. In each set of five wires, only four of the five wires in each set of auxiliary wires are used in each mode of heater operation and one of the five wires in each set is bypassed. 
     The first set of main power supply wire  622  and main power return wire  624  are connected to the fifth modular heater assembly. In the fifth modular heater assembly, the third heater  654  is the master control heater whose thermocouple junction  635  and temperature sensing wire  632  are used for temperature sensing. The third heater  654  functions as both a heater and a temperature sensor by selectively using the temperature sensing wire  632 ′ for the third heater  654  to form a part of the electric circuit. The temperature sensing wires  632  of the first and second heaters  650 ,  652  are bypassed and the first and second heaters perform the function of a heater only. The second set of main power supply wire  622  and the main power return wire  624  connect only one heater, i.e., the fourth heater  656 , to the controller  610 . The thermocouple junction  635  and the temperature sensing wire  632  of the fourth heater  656  are also used for measuring temperature of the fourth heater  656 . 
     Unlike the wire harness  612 ,  612 ′,  612 ″,  720  in the first to fourth modular heater assembly, the wire harness  722  of the present form includes a plurality pairs of connectors  614 ,  614 ′,  616 ,  616 ′,  618 ,  618 ′,  620 ,  620 ′ corresponding to the plurality of heaters  650 ,  652 ,  654 ,  656 . Each heater is connected to a pair of connectors. Moreover, the temperature sensing wire is attached to the auxiliary power return wire, not the auxiliary power supply wire, in each set of the auxiliary wires extending from the heater. Therefore, the thermocouple junction is formed between the auxiliary power return wire  636 ′ and a temperature sensing wire  632 ′ in each of the sets of auxiliary wires. The temperature sensing wires  632 ′ and the main power return wires  624 ′ are made of the first conductive material (e.g., Constantan), and the remaining wires are made of the second conductive material (e.g., Chromel®). The main power return wires  624 ′ are considered extensions of the temperature sensing wires  632 ′ for temperature sensing purposes. 
     Referring to  FIG.  28   , a heater system  710  including a power control system  600 ′″ and a plurality of heaters  650 ,  652 ,  654 ,  656  connected and controlled by the power control system  600 ′″ is shown. The power control system  600 ′″ includes a wire harness  720 , which includes two sets of main power supply wires  622  and main power return wires  624  for routing one of the heaters (i.e., the fourth heater  656 ) as a stand-alone heater, and the remaining ones of the heaters (i.e., the first, second and third heaters  650 ,  652 ,  654 ) in a series connection. The first, second and third heaters  650 ,  652 ,  654  are connected in series in this order to form a sixth modular heater assembly. In the sixth modular heater assembly, the second heater  652  is the master control heater whose thermocouple junction  635  and temperature sensing wire  632 ′ are used for temperature measurement and temperature signal transmission. The master control heater is disposed in the center of the sixth modular heater assembly. The first set of main power supply wire  622  and main power return wire  624  are connected to the sixth modular heater assembly. The second set of main power supply wire  622  and the main power return wire  624  connect only the fourth heater  656  to the controller  610  such that the fourth heater becomes a stand-alone heater. 
     Three connectors and six auxiliary wires are used for connecting the second heater  652  to the controller  610 , to the first heater  650 , and the third heater  654 . Two connectors and five auxiliary wires are used for connecting each of the first heater  650  and the third heater  654  to another heater. Two connectors and five auxiliary wires are used for connecting the fourth heater  656  to the controller  610 . Each set of the auxiliary wires for the first heater  650 , the third heater  654  and the fourth heater  656  includes five wires, including a temperature sensing wire  632 ′, an auxiliary power supply wire  634 ′, an auxiliary power return wire  636 ′, a first routing wire  660 , and a second routing wire  662 , similar to that of  FIG.  27   . However, the set of auxiliary wires for the second heater  652 , which is used as the main control heater, includes six wires. The six wires include a temperature sensing wire  632 ′, an auxiliary power supply wire  634 ′, and four routing wires  664 . All of the six wires are used in each mode of heater operation. 
     In the present form, the thermocouple junction  635  for the second heater  652  is formed between the temperature sensing wire  632 ′ and the resistive heating element  637 . The thermocouple junctions  635  for the first and third heaters  650 ,  654  are formed between the temperature sensing wires  632 ′, the auxiliary power supply wires  634 ′, and the resistive heating elements  637 . The thermocouple junction  635  for the fourth heater  656  is formed between the temperature sensing wire  632 ′, the auxiliary power return wire  636 ′, and the resistive heating element  637 . All of the temperature sensing wires  632 ′ and the two main power return wires  624  are made of the first conductive material (Material A, such as Constantan), whereas the remaining wires (including the two main power supply wires  622 , the connecting wires  640  connecting to the same or adjacent connectors, the auxiliary power supply wires  634 ′, the auxiliary power return wires  636 ′ and the routing wires  660 ,  662 ) are made of a second conductive material (Material B, such as Chromel®). 
     In summary, the power control system  600 ,  600 ′,  600 ″, or  600 ′″ constructed in accordance with the teachings of the present disclosure include a wire harness  612 ,  612 ′,  612 ″,  720 ,  722 , or  724  that allows the various wires to be routed via connectors to achieve various wiring connections. Some or all of a plurality of heaters may be connected in series in different orders, while the other heaters may be routed as stand-alone heaters and controlled independently from other heaters. While not shown in any of the forms, it is understood that the wire harness may include a plurality sets of main power supply wires and main power return wires corresponding to the plurality of heaters. Each set of main power supply wire and main power return wire connects only one heater to the controller such that each heater becomes a stand-alone heater and is controlled independently. 
     Moreover, the power control system includes a plurality sets of auxiliary wires disposed between the plurality of connectors and the heaters. The auxiliary wires may be always attached to the heaters and adjacent connector part (whether a male part or a female part) of the connectors to form a plurality of modular heater units. The plurality of modular heater units may be easily connected in series in any order or as stand-alone heaters by connecting the connector parts to another connector parts via proper wiring. Therefore, the wire harness improves modularity of the plurality of heaters. 
     Further, in some forms, each of the plurality sets of auxiliary wires includes three wires including a temperature sensing wire, an auxiliary power supply wire, and an auxiliary power return wire. Two of the three wires are joined to form a thermocouple junction. One of the two wires that are joined is selected to form a part of the electric circuit depending on whether the associate heater is used as a heater only or as both a heater and a temperature sensor in the electric circuit. The three-wire mechanism extending from each heater allows each heater to selectively function as both a heater and a temperature sensor, thereby eliminating the use of additional temperature sensors in the heater system and providing a heater system with a simpler design. 
     In other forms, the sets of auxiliary wires may include five wires or six wires. In addition to the temperature sensing wire, the auxiliary power supply wire, and the auxiliary power return wire, additional routing wires may be included in each set of auxiliary wires to increase the routing options in order to connect these heaters in different orders and to use any one of the heaters as the master control heater, which is used as both a heater and a temperature sensor. 
     In the figures, the direction of an arrow, as indicated by the arrowhead, generally demonstrates the flow of information (such as data or instructions) that is of interest to the illustration. For example, when element A and element B exchange a variety of information, but information transmitted from element A to element B is relevant to the illustration, the arrow may point from element A to element B. This unidirectional arrow does not imply that no other information is transmitted from element B to element A. Further, for information sent from element A to element B, element B may send requests for, or receipt acknowledgements of, the information to element A. 
     In this application, the term “module” and/or “controller” may refer to, be part of, or include: an Application Specific Integrated Circuit (ASIC); a digital, analog, or mixed analog/digital discrete circuit; a digital, analog, or mixed analog/digital integrated circuit; a combinational logic circuit; a field programmable gate array (FPGA); a processor circuit (shared, dedicated, or group) that executes code; a memory circuit (shared, dedicated, or group) that stores code executed by the processor circuit; other suitable hardware components that provide the described functionality; or a combination of some or all of the above, such as in a system-on-chip. 
     The term memory is a subset of the term computer-readable medium. The term computer-readable medium, as used herein, does not encompass transitory electrical or electromagnetic signals propagating through a medium (such as on a carrier wave); the term computer-readable medium may therefore be considered tangible and non-transitory. Non-limiting examples of a non-transitory, tangible computer-readable medium are nonvolatile memory circuits (such as a flash memory circuit, an erasable programmable read-only memory circuit, or a mask read-only circuit), volatile memory circuits (such as a static random access memory circuit or a dynamic random access memory circuit), magnetic storage media (such as an analog or digital magnetic tape or a hard disk drive), and optical storage media (such as a CD, a DVD, or a Blu-ray Disc). 
     The apparatuses and methods described in this application may be partially or fully implemented by a special purpose computer created by configuring a general-purpose computer to execute one or more particular functions embodied in computer programs. The functional blocks, flowchart components, and other elements described above serve as software specifications, which can be translated into the computer programs by the routine work of a skilled technician or programmer. 
     Unless otherwise expressly indicated herein, all numerical values indicating mechanical/thermal properties, compositional percentages, dimensions and/or tolerances, or other characteristics are to be understood as modified by the word “about” or “approximately” in describing the scope of the present disclosure. This modification is desired for various reasons including industrial practice; material, manufacturing, and assembly tolerances; and testing capability. 
     As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A OR B OR C), using a non-exclusive logical OR, and should not be construed to mean “at least one of A, at least one of B, and at least one of C.” 
     The description of the disclosure is merely exemplary in nature and, thus, variations that do not depart from the substance of the disclosure are intended to be within the scope of the disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure.