Modular heater assembly with interchangeable auxiliary sensing junctions

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.

FIELD

The present disclosure relates to resistive heaters and to temperature sensing devices such as thermocouples.

BACKGROUND

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

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.

DETAILED DESCRIPTION

Referring toFIG.1, a heater according to the teachings of the present disclosure is illustrated and generally indicated by reference numeral20. The heater20in 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 heater20comprises a resistive heating element22having two end portions24and26, and the resistive heating element22is in the form of a metal wire, such as a nichrome material by way of example. The resistive heating element22is wound or disposed around a non-conductive portion (or core in this form)28. The core28defines a proximal end30and a distal end32and further defines first and second apertures34and36extending through at least the proximal end30.

The heater20further comprises a first power pin40that is made of a first conductive material and a second power pin42that is made of a second conductive material that is dissimilar from the first conductive material of the first power pin40. Further, the resistive heating element22is made of a material that is different from the first and second conductive materials of the first and second power pins40,42and forms a first junction50at end24with the first power pin40and a second junction52at its other end26with the second power pin42. Because the resistive heating element22is a different material than the first power pin40at junction50and is a different material than the second power pin42at junction52, a thermocouple junction is effectively formed and thus changes in voltage at the first and second junctions50,52are detected (as set forth in greater detail below) to determine an average temperature of the heater20without the use of a separate/discrete temperature sensor.

In one form, the resistive heating element22is a nichrome material, the first power pin40is a Chromel® nickel alloy, and the second power pin42is an Alumel® nickel alloy. Alternately, the first power pin40could be iron, and the second power42could 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 element22, the first power pin40, and the second power pin42, as long as the three materials are different and a thermocouple junction is effectively formed at junctions50and52. 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 heater20may 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 heater20and a possible premature failure.

As further shown, the heater20includes a sheath60surrounding the non-conductive portion28and a sealing member62disposed at the proximal end30of the non-conductive portion28and extending at least partially into the sheath60to complete the heater assembly. Additionally, a dielectric fill material64is disposed between the resistive heating element22and the sheath60. 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 toFIG.2, the present disclosure further includes a controller70in communication with the power pins40,42and configured to measure changes in voltage at the first and second junctions50,52. More specifically, the controller70measures millivolt (mV) changes at the junctions50,52and then uses these changes in voltage to calculate an average temperature of the heater20. In one form, the controller70measures changes in voltage at the junctions50,52without interrupting power to the resistive heating element22. 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 controller70switches from a heating mode to a measuring mode to measure the changes in voltage. Once the average temperature is determined, the controller70switches 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 heater20, 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 inFIG.3, a FET72is 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 resistors73,74, and75are used to form a protective circuit for the measurement circuit76. 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 toFIG.2, a pair of lead wires80are connected to the first power pin40and the second power pin42. In one form, the lead wires80are both the same material such as, by way of example, copper. The lead wires80are provided to reduce the length of power pins needed to reach the controller70, while introducing another junction by virtue of the different materials at junctions82and84. In this form, in order for the controller70to determine which junction is being measured for changes in voltage, signal wires86and88may be employed such that the controller70switches between the signal wires86and88to identify the junction being measured. Alternately, the signal wires86and88may be eliminated and the change in voltage across the lead wire junctions82and84can be negligible or compensated through software in the controller70.

Referring now toFIG.4, the teachings of the present disclosure may also be applied to a heater20′ having a plurality of zones90,92and94. Each of the zones includes its own set of power pins40′,42′ and resistive heating element22′ as described above (only one zone90is illustrated for purposes of clarity). In one form of this multi-zone heater20′, the controller70(not shown) would be in communication with the end portions96,98, and100of each of the zones in order to detect voltage changes and thus determine an average temperature for that specific zone. Alternately, the controller70could be in communication with only the end portion96to determine the average temperature of the heater20′ 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 toFIG.5, the teachings of the present disclosure may also be applied to a plurality of separate heaters100,102,104,106, and108, 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 heater100,102,104,106, and108can be determined by a controller70as set forth above. In another form, each of the heaters100,102,104,106, and108has 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 toFIGS.6and7, a pitch of the resistive heating element110may be varied in accordance with another form of the present disclosure in order to provide a tailored heat profile along the heater120. In one form (FIG.5), the resistive heating element110defines a continuously variable pitch along its length. More specifically, the resistive heating element110has a continuously variable pitch with the ability to accommodate an increasing or decreasing pitch P4-P9on the immediately adjacent next 360 degree coil loop. The continuously variable pitch of resistive heating element110provides gradual changes in the flux density of a heater surface (e.g., the surface of a sheath112). Although the principle of this continuously variable pitch is shown as applied to a tubular heater having filled insulation114, 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 pin122is made of a first conductive material, the second power pin124is made of a second conductive material that is dissimilar from the first conductive material of the first power pin122, while the resistive heating element110is made of a material that is different from the first and second conductive materials of the first and second power pins122,124so that changes in voltage at the first and second junctions126,128are detected to determine an average temperature of the heater120.

In another form (FIG.7), the resistive heating element130has pitches P1, P2, and P3in zones A, B, and C, respectively. P3is greater than P1, and P1is greater than P2. The resistive heating element130has a constant pitch along the length of each zone as shown. Similarly, the first power pin132is made of a first conductive material, the second power pin134is made of a second conductive material that is dissimilar from the first conductive material of the first power pin132, while the resistive heating element130is made of a material that is different from the first and second conductive materials of the first and second power pins132,134so that changes in voltage at the first and second junctions136,138are detected to determine an average temperature of the heater120.

Referring toFIG.8, the heater and dual purpose power pins as described herein have numerous applications, including by way of example a heat exchanger140. The heat exchanger140may include one or a plurality of heating elements142, and each of the heating elements142may 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 inFIG.9, the teachings of the present disclosure may also be applied to other types of heaters such as a layered heater150. Generally, the layered heater150includes a dielectric layer152that is applied to a substrate154, a resistive heating layer156applied to the dielectric layer152, and a protective layer158applied over the resistive heating layer156. A junction160is formed between one end of a trace the resistive layer158and a first lead wire162(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 heater150. 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 toFIG.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

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 inFIGS.11-13, wherein a heater for use in fluid immersion heating is illustrated and generally indicated by reference numeral200. The heater200comprises a heating portion202configured for immersion into a fluid, the heating portion202comprising a plurality of resistive heating elements204, and at least two non-heating portions206,208contiguous with the heating portion202(only one non-heating portion206is shown inFIG.11). Each non-heating portion206,208defines a length and comprises a corresponding plurality of sets of power pins electrically connected to the plurality of heating elements204. More specifically, each set of power pins comprises a first power pin212made of a first conductive material and a second power pin214made of a second conductive material that is dissimilar from the first conductive material of the first power pin212. The first power pins212are electrically connected to the second power pins214within the non-heating portions206,208to form junctions220,230, and240. As further shown, the second power pins214extend into the heating portion202and are electrically connected to the corresponding resistive heating elements204. Further, the second power pins214define a cross-sectional area that is larger than the corresponding resistive heating element204so as to not create another junction or measurable amount of heat at the connection between the second power pins24and the resistive heating elements204.

As further shown, a termination portion250is contiguous with the non-heating portion206, and the plurality of first power pins212exit the non-heating portion206and extend into the termination portions250for electrical connection to lead wires and a controller (not shown). Similar to the previous description, each of the resistive heating elements204are made of a material that is different from the first and second conductive materials of the first and second power pins212,214, and wherein each of the junctions220,230, and240of the first power pin212to the second power pin214is disposed at a different location along the lengths of the non-heating portions206,208. More specifically, and by way of example, junction220is at a distance L1, junction230is at a distance L2, and junction240is at a distance L3.

As shown inFIG.13, with temperature of the junctions220,230, and240over time “t,” the junction220is submerged in the fluid F, the junction230is submerged but not as deep in the fluid, and the junction240is not submerged. Accordingly, detecting changes in voltage at each of the junctions220,230, and240can provide an indication of the fluid level relative to the heating portion202. It is desirable, especially when the fluid is oil in a cooking/fryer application, that the heating portion202not be exposed to air during operation so as to not cause a fire. With the junctions220,230, and240according to the teachings of the present disclosure, a controller can determine if the fluid level is too close to the heating portion202and thus disconnect power from the heater200.

Although three (3) junctions220,230, and240are 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 portion202.

Referring now toFIG.14, yet another form of the present disclosure includes a plurality of heater cores300arranged in zones of a heater system270as shown. The heater cores300in 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 core300includes a plurality of power pins301,302,303,304, and305as shown. Similar to the forms described above, the power pins are made of different conductive materials, and more specifically, power pins301,304, and305are made of a first conductive material, power pins302,303, and306are made of a second conductive material that is dissimilar from the first conductive material. As further shown, at least one jumper320is connected between dissimilar power pins, and in this example, power pin301and power pin303, in order to obtain a temperature reading proximate the location of the jumper320. The jumper320may be, for example, a lead wire or other conductive member sufficient to obtain the millivolt signal indicative of temperature proximate the location of the jumper320, which is also in communication with the controller70as illustrated and described above. Any number of jumpers320may be used across dissimilar power pins, and another location is illustrated at jumper322between power pin303and power pin305, between ZONE3and ZONE4.

In this exemplary form, power pins301,303, and305are neutral legs of heater circuits between adjacent power pins302,304, and306, respectively. More specifically, a heater circuit in ZONE1would be between power pins301and302, with the resistive heating element (e.g., element22shown inFIG.1) between these power pins. A heater circuit in ZONE2would be between power pins303and304, with the resistive heating element between these two power pins. Similarly, a heater circuit in ZONE3would be between power pins305and306, 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 toFIG.1. Any number and configurations of heater circuits with multiple heater cores300and 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 toFIG.15, in one form, a heater400is configured to include a primary sensing junction that can be arranged within the heater400or outside the heater400for measuring temperature. The heater400includes a resistive heating element402, a first power pin404, and a second power pin406. The resistive heating element402has a first end and a second end. The first power pin402is connected to the first end of the resistive heating element402to form a first junction408, and the second power pin406is connected to the second end of the resistive heating element402to form a second junction410. The first power pin404and the second power pin406are operable to supply power to the heating element402by way of the controller.

The second power pin406includes a first lead wire412and a second lead wire414. The first lead wire412is connected to the second end of the resistive heating element402to form the second junction410, and the second lead wire414is connected to the first lead wire412to form a primary sensing junction416at a first reference area. The second lead wire414is configured to connect the resistive heating element402to the controller by way of the first lead wire412.

In one form, the first lead wire412and the second lead wire414are 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 wire412and the second lead wires414is represented by the different style lines inFIG.15(e.g., dash line for the second lead wire414and dashed-dotted line for first lead wire412). Since the materials are different, the primary sensing junction416is 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 junctions408and410for connecting to the resistive heating element402is separated from a sensing location. Thus, the heater400is not restricted to detecting temperature at the ends of the heating element402, and a temperature measurement may be detected at various locations within the heater400. Furthermore, in one form, the first lead wire412and the second lead wire414are configured to have the primary sensing junction416outside of the heater400.

As discussed with respect toFIG.2, the controller (not shown inFIG.15) is in communication with the first power pin404and the second power pin406and is configured to supply power to the resistive heater element402via the power pins404and406. The controller is also configured to calculate the temperature at the first reference area based on the voltage change created by the sensing junction416using the Seebeck coefficients of the materials.

In one form, the resistive heating element402, the first power pin404, and the first lead wire412of the second power pin406are 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 junction408and the second junction410is substantially zero, and the temperature measurement determined by the controller is based on the voltage change created by the primary sensing junction416.

In another form, the resistive heating element402, the first power pin404, and/or the first lead wire412of the second power pin406are made of different conductive materials. With such configurations, the material of the second lead wire414is selected such that the Seebeck coefficient of the second lead wire414is the most dissimilar from that of the resistive heating element402, the first power pin404, and the first lead wire412of the second power pin406. Accordingly, the primary sensing junction416is provided as the largest contributor to overall temperature measurement, and any temperature measurement from the first and second junctions408and410are 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 junction416to determine the temperature at the reference area.

Referring toFIG.16, in one form, a heater420includes two sensing junctions in proximity to each other to detect a temperature at a virtual point between the two sensing junctions. Here, the heater420comprises a resistive heating element422, a second power pin424, and a first power pin426. The resistive heating element422comprises a first end and a second end. The first power pin426forms a first junction428with the first end of the heating element422, and the second power pin424forms a second junction430with the second end of the heating element422. The second power pin424is configured in a similar manner as the second power pin406ofFIG.15, and thus, includes a first lead wire432that is connected to the resistive heating element422to form the second junction430, and a second lead wire434that is connected to the first lead wire432to form a first primary sensing junction440at a first reference area within the heater420.

In this form, the first power pin426is configured in a similar manner as the second power pin424, and comprises two lead wires (i.e., a third lead wire436and a fourth lead wire438) to form a sensing junction. More particularly, the third lead wire436is connected to the first end of the resistive heating element422to form the first junction428, and the fourth lead wire438forms a second primary sensing junction442with the third lead wire436at a second reference area. The second primary sensing junction442is provided at a second reference area of the heater420that is adjacent and proximate to the first reference area having the first primary sensing junction440. While the sensing junctions440and442are provided as within the heater420, the sensing junctions440and442can also be provided outside the heater420.

Similar to the second power pin424, the third lead wire436is made of a different conductive material than that of the fourth lead wire438, and is of different conductive material as that of the second lead wire434of the second power pin424. Accordingly, the second primary sensing junction442is 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 element422, the first lead wire432of the second power pin424, and the third lead wire436of the first power pin426are made of the same conductive material or of materials with similar Seebeck properties, such that a voltage change created by the first junction428and the second junction430is substantially zero, and the temperature measurement determined by the controller is based on the voltage changes at the sensing junctions440and442.

The controller (not shown inFIG.16) is configured to supply power to the heating element422via the first power pin426and the second power pin424, and to measure a temperature at a virtual point between the two sensing junctions440and442based on the voltage changes created by the junctions440and442. 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 toFIG.17AandFIG.17B, 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.17Aillustrates a cartridge heater450that includes a resistive heating element452in the form of a metal wire, a first power pin454, and a second power pin456. The cartridge heater450is configured to include two sensing junctions provided outside of the heater450to measure a temperature at a virtual point between the two sensing junctions.

More particularly, in one form, the resistive heating element452is wound or disposed around a non-conductive portion (or a core in this form) as discussed with respect toFIG.1. The first power pin454comprises a first lead wire458and a second lead wire460. The first lead wire458is connected to the first end of the resistive heating element452to form a first junction462, and the second lead wire460forms a first primary sensing junction464with the first lead wire458at a first reference area outside the heater450. The second power pin456comprises a third lead wire466and a fourth lead wire468. The third lead wire466is connected to the resistive heating element452to form a second junction470. The fourth lead wire468is connected to the third lead wire466to form a second primary sensing junction472at a second reference area outside the heater450. The first and second primary sensing junctions464and472are positioned adjacent and in proximity to one another.

In one form, the resistive heating element452, the first lead wire458of the first power pin454, and the third lead wire466of the second power pin456are made of the same material or of materials having similar Seebeck properties, and are different from the material of the second lead wire460of the first power pin454and the fourth lead wire468of the second power pin456. In addition, the material of the second lead wire460of the first power pin454is different from the material of the fourth lead wire468of the second power pin456. Accordingly, the first and second primary junctions464and472operate as thermocouples to detect a temperature at a virtual point between the two junctions464and472.

FIG.17Billustrates a cartridge heater480having one primary sensing junction located within the heater. The cartridge heater480includes a resistive heating element482having two ends, a first power pin484, and a second power pin486. The first power pin484forms a first junction488with a first end of the heating element482and the second power pin486forms a second junction490with a second end of the heating element482. Similar to the heater ofFIG.15, the second power pin486includes a first lead wire492and a second lead wire494, which are made of different material (i.e., have different Seebeck coefficients). The first lead wire492is connected to the second end of the resistive heating element482to form the second junction490, and the second lead wire494is connected to the first lead wire492to form a primary sensing junction496at a first reference area within the heater480. Accordingly, the primary sensing junction490is operable as a thermocouple to measure a temperature at the first reference area.

In one form, the resistive heating element482, the first power pin484, and the first lead wire492of the second power pin486are made of the same conductive material or of materials having similar Seebeck properties. Accordingly, a voltage change created by the first junction488and the second junction490is substantially zero, and the temperature measurement determined by the controller is based on the voltage change created by the primary sensing junction490.

Referring toFIG.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 heater500is operable to heat a fluid (e.g., a gas) following through a tube, and comprises a resistive heating (i.e., thermal) element502(shown with phantom lines), a first power pin504, and a second power pin506. While not fully illustrated inFIG.18, the resistive heating element502is configured to extend through the heater500, and is protected by a cover. The first power pin504and the second power pin506extend into the cover of the heater500to form a first junction with a first end of the heating element502and a second junction with a second end of the heating element502, respectively.

The resistive heating element502is 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 element502is made of a high temperature coefficient of resistance (TCR) material. A controller (not shown inFIG.18) is in communication with the first and second power pins504and506, and configured to measure voltage (i.e., mV) changes across the power pins504and506. Using the voltage change, the controller calculates an average temperature of the resistive heating element502(e.g., about R1).

The first power pin504includes a first lead wire508and a second lead wire510, which are made of different materials (i.e., have different Seebeck coefficients). The first lead wire508forms the second junction with the heating element502, and the second lead wire510forms a primary sensing junction512with the first lead wire508at a second reference area that is along an outer surface (i.e., R2) of the heater500(i.e., along a plane that is different than that of the heating element502). Accordingly, the primary sensing junction512is operable as a thermocouple to measure a temperature at the second reference area based on a voltage change created by the sensing junction512. The resistive heating element502, the second power pin506, and the first lead wire508of the first power pin504are 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 heater500based on the temperature measurement of the heating element502, the temperature at the primary sensing junction512, and power delivered to the heater500from 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 pins506and504, 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 junction512and the Seebeck coefficient of the first and second lead wire508and510. 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 heater500(e.g., any location within the heater). In addition, if the geometry of the heater500is known, the controller can also be configured to determine a heat flux between the inner surface and the outer surface of the heater500. 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 heater500is 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 heater500is energized, the heater500is substantially at room temperature, such that the primary sensing junction512is at the same or substantially the same temperature as the high TCR element wire (i.e., the heating element502). The controller is configured to measure the temperature using the primary sensing junction512, and further measure the resistance of the heating element502. The controller associates the resistance of the heater500with the temperature measured by the primary sensing junction512, and uses this baseline value to covert other resistances to a temperature, thereby calibrating the heater element502.

Referring toFIG.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 junction550is formed by a first lead wire552and a second lead wire554that are made of different materials. The sensing junction550has a planar shape (i.e., flat) and is surrounded by a heat diffuser556that 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 toFIG.20, a heater system700including a power control system600and a plurality of heaters602,604,606,608connected and controlled by the power control system600is shown. The power control system600includes a controller610, a wire harness612, and a plurality sets of auxiliary wires632,634,636connected to and extending from the plurality of heaters. The wire harness612and the plurality sets of auxiliary wires632,634,636connect the controller610to the plurality of heaters602,604,606,608. The plurality of heaters include a first heater602, a second heater604, a third heater606, and a fourth heater608. The wire harness612may be used to connect some or all of the plurality of heaters602,604,606, and608in 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 harness612, and the heaters may be any type of heaters without departing from the scope of the present disclosure. The controller610is configured to supply power to the plurality of heaters602,604,606,608, determine temperatures of the plurality of heaters602,604,606,608based on temperature signals transmitted from the heaters, and control the temperatures of the plurality of heaters602,604,606,608based on the measured temperatures and target temperatures.

The wire harness612includes a plurality of connectors614,616,618,620and a plurality of electrical wires for connecting the controller610to the plurality of heaters602,604,606,608. In one form, the plurality of connectors614,616,618,620may 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 ofFIG.20, the number of the plurality of connectors614,616,618,620is equal to the number of the plurality of heaters602,604,606,608such that each of the heaters is connected to another heater(s) or the controller610via a corresponding connector.

In the illustrative example ofFIG.20, the plurality of electrical wires include a main power supply wire622, a main power return wire624, and a plurality of connecting wires626,628,630. The main power supply wire622and the main power return wire624are directly connected to the controller610for routing electric current to and out of the plurality of heaters602,604,606,608, respectively. The plurality of connecting wires include a first connecting wire426, a second connecting wire428, and a third connecting wire430for connecting one of the connectors614,616,618,620to another one of the connectors614,616,618,620. The plurality sets of auxiliary wires are disposed between the connectors614,616,618,620and the plurality of heaters602,604,606,608. 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 toFIG.21A, 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 junction635, which is also joined to an end of a resistive heating element637of the heater602. More specifically, each set of auxiliary wires includes a temperature sensing wire432, an auxiliary power supply wire634, and an auxiliary power return wire636. The temperature sensing wire632is made of a first conductive material (as shown in dashed line), whereas the auxiliary power supply wire634and the auxiliary power return wire634are made of a second conductive material (as shown in solid lines) different from the first conductive material.

The temperature sensing wire632(made of the first conductive material) is joined to one of the auxiliary power supply wire634and the auxiliary power return wire634(made of the second conductive material) to form a thermocouple junction635therebetween. As shown inFIG.21A, the temperature sensing wire632of each set of auxiliary wires is joined to the auxiliary power supply wire634and joined to one of a pair of terminal areas of a resistive heating element637to form a thermocouple junction635therebetween. The auxiliary power return wire636is connected to the other one of the terminal areas of the resistive heating element637. As such, electric current flows from the temperature sensing wire632, through the resistive heating element637, to the auxiliary power return wire636. The three wires may be fixed to the terminal areas of a resistive heating element637of 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 connectors614,616,618,620each including a first connector part and a second connector part. For example, as shown inFIG.21A, the connector614includes a first connector part614aand a second connector part614b. 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 controller610via connecting wire(s), the main power supply wire, or the main power return wire. As shown inFIG.21Ain conjunction withFIG.20, the temperature sensing wire632and the auxiliary power return wire636for the first heater602are used to carry electric current and the auxiliary power supply wire634is bypassed. As clearly shown inFIG.20, the auxiliary power supply wires634and the auxiliary power return wires636for the other heaters604,606,608are used to carry electric current and the temperature sensing wires632are bypassed. The thermocouple junction635on the first heater602measures the temperature of the first heater, and the temperature sensing wire632and the auxiliary power return wire636for the first heater602transmit a signal relating to the temperature of the heater to the controller610.

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 toFIG.21B, each of the connectors614,616,618,620may include a first connector part and a mating second connector part (which may be a socket and plug assembly, for example). For example, the connector614may include a first connector part614aand a second connector part614b. The heater602and the corresponding set of auxiliary wires (i.e., the temperature sensing wire632, the auxiliary power supply wire634, and the auxiliary power return wire636) are attached to the first connector part614ato form a modular heater unit603. The modular heater unit603can be easily connected to other electrical components, such as another modular heater unit or the controller610, 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 ofFIG.20, the second, third and fourth heaters604,606,608are connected by the wire harness612in 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 heaters604,606,608, the auxiliary power supply wires634and the auxiliary power return wires636are selectively used to form a part of the electric circuit, whereas the temperature sensing wires632are bypassed. The first heater602is used as both a heater and a temperature sensor by selectively using the temperature sensing wire632and the auxiliary power supply wire634to form a part of the electric circuit, and by bypassing the auxiliary power supply wire634. During the temperature sensing mode, the thermocouple junction635on the first heater602is used to measure a temperature of the heater, and the temperature sensing wire632and the auxiliary power return wire636for the first heater and other wires in the electric circuit are used to transmit a temperature signal to the controller610.

Referring toFIG.22, an electric diagram illustrating the electric circuit of the heater system700including the power control system600and the plurality of heaters ofFIG.20is shown. The plurality of heaters602,604,606, and608are connected in series in this order to form a first modular heater assembly. The main power supply wire622is made of the same first conductive material of the temperature sensing wires632as shown in dashed line. The main power return wire624and the connecting wires626,628,630are made of the same second conductive material of the auxiliary power supply wire634and the auxiliary power return wire636as 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 system600is in the power mode, the power is supplied from CH2+ of the controller610through the main power supply wire622, the temperature sensing wire632and the auxiliary power return wire636of the first heater602, the connecting wire626, the auxiliary power supply wire634and the auxiliary power return wire636of the second heater604, the connecting wire628, the auxiliary power supply wire634and the auxiliary power return wire636of the third heater606, the connecting wire630, the auxiliary power supply wire634and the auxiliary power return wire636of the fourth heater608. The electric current returns to CH2− of the controller610through the main power return wire624.

When the control system600is in the temperature sensing mode, the electric current path is the same as that in the power supply mode. The thermocouple junction635of the first heater602is used to measure a temperature of the first heater602. The temperature of the first heater602is 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 controller610via the temperature sensing wire632and the auxiliary power return wire636of the first heater602and the other wires forming the circuit.

Only one of the thermocouple junctions635in the first modular heater assembly is used for temperature sensing. In the first modular heater assembly, the thermocouple junction635in the first heater602that is directly connected to the controller610by the main power supply wire622is used for temperature sensing. The main power supply wire622is made of the same first conductive material of the temperature sensing wire632and may be considered an extension of the temperature sensing wire in the first modular heater assembly.

Referring toFIG.23, a heater system702including a power control system600and a plurality of heaters602,604,606,608connected and controlled by the power control system600is shown. The power control system600includes a wire harness612′, which routes the plurality of heaters602,604,606,608in 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 heater604, the first heater602, the third heater606, and the fourth heater608are connected in series in this order to form a second modular heater assembly and the power is supplied to the second heater604first. In this wiring connection, only the second heater604is used as both a heater and a temperature sensor by selectively using the temperature sensing wire632and the auxiliary power return wire636for the second heater to form a part of the electric circuit. The other heaters602,606,608are used to perform only the function of heaters by selectively using the auxiliary power supply wires634and the auxiliary power return wires636to form a part of the circuit and by bypassing the temperature sensing wires. Only the thermocouple junction635of the second heater604is used for temperature sensing of the second modular heater assembly. Like the first modular heater assembly ofFIG.20, the main power supply wire622and the temperature sensing wires632are 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 wire622may be considered an extension of the temperature sensing wire632for the second heater604for temperature sensing purposes.

Referring toFIG.24, a heater system704including a power control system600and a plurality of a heaters602,604,606,608connected and controlled by the power control system600is shown. The power control system600includes a wire harness612″, which routes the plurality of heaters602,604,606and608in a third series connection. In this wiring connection, the third heater606, the second heater604, the first heater602, and the fourth heater608are connected in series in this order to form a third modular heater assembly and the power is supplied to the third heater606first. In this wiring connection, only the third heater606is used to perform the function of both a heater and a temperature sensor and the thermocouple junction635of the third heater606is used for temperature sensing. The other heaters602,604,608are used as heaters only by bypassing the temperature sensing wires632associated with these heaters. Similarly, the main power supply wire622and the temperature sensing wires632are 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 wire622may be considered an extension of the temperature sensing wire632for the third heater606for temperature sensing purposes.

Referring toFIGS.25and26, a heater system706including a power control system600′ and a plurality of a heaters602,604,606,608connected and controlled by the power control system600is shown. The power control system600′ includes a wire harness720, which includes two sets of main power supply wires622and main power return wires624for routing one of the heaters (i.e., the fourth heater608) as a stand-alone heater, and the remaining ones of the heaters (i.e., the first, second and third heaters602,604,606) in a series connection.

The first set of main power supply and return wires connect the first heater602, the second heater604, the third heater608in series in this order to form a fourth modular heater assembly and the power is supplied from the controller610to the first heater602first. The second set of main power supply and return wires directly connect the fourth heater608to the controller610such that the fourth heater408becomes a stand-alone heater. The fourth heater608is controlled independently from the fourth modular heater assembly.

In this fourth modular heater assembly, only the first heater602is used as both a heater and a temperature sensor and the thermocouple junction635of the first heater602is 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 junction635of the fourth heater is also used for measuring temperature of the fourth heater608.

Similarly, the two main power supply wires622and the temperature sensing wires632are made of the first conductive material (such as Constantan), and the remaining wires are made of the second conductive material (such as Chromel®).

Referring toFIG.27, a heater system708including a power control system600″ and a plurality of heaters650,652,654,656connected and controlled by the power control system600″ is shown. The power control system600″ includes a plurality sets of auxiliary wires632′,634′,636′,660,662attached to the plurality of heaters650,652,654,656, and a wire harness722for connecting the plurality sets of auxiliary wires to the controller610. The wire harness722includes two sets of main power supply wires622and main power return wires624for routing one of the heaters (e.g., the fourth heater656) as a stand-alone heater, and the remaining ones of the heaters (i.e., the first, second and third heaters650,652,654) in a series connection. The first heater650, the second heater652, and the third heater654are 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 wire632′, an auxiliary power supply wire634′, an auxiliary power return wire636′, a first routing wire660, and a second routing wire662. The structure and function of the temperature sensing wire632′, the auxiliary power supply wire634′ and the auxiliary power return wire636′ are the same as that of the temperature sensing wire632, the auxiliary power supply wire634, and the auxiliary power return wire636and thus the detailed description thereof is omitted herein for clarity. The first routing wire660and the second routing wire662in 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 wire622and main power return wire624are connected to the fifth modular heater assembly. In the fifth modular heater assembly, the third heater654is the master control heater whose thermocouple junction635and temperature sensing wire632are used for temperature sensing. The third heater654functions as both a heater and a temperature sensor by selectively using the temperature sensing wire632′ for the third heater654to form a part of the electric circuit. The temperature sensing wires632of the first and second heaters650,652are bypassed and the first and second heaters perform the function of a heater only. The second set of main power supply wire622and the main power return wire624connect only one heater, i.e., the fourth heater656, to the controller610. The thermocouple junction635and the temperature sensing wire632of the fourth heater656are also used for measuring temperature of the fourth heater656.

Unlike the wire harness612,612′,612″,720in the first to fourth modular heater assembly, the wire harness722of the present form includes a plurality pairs of connectors614,614′,616,616′,618,618′,620,620′ corresponding to the plurality of heaters650,652,654,656. 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 wire636′ and a temperature sensing wire632′ in each of the sets of auxiliary wires. The temperature sensing wires632′ and the main power return wires624′ 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 wires624′ are considered extensions of the temperature sensing wires632′ for temperature sensing purposes.

Referring toFIG.28, a heater system710including a power control system600′″ and a plurality of heaters650,652,654,656connected and controlled by the power control system600′″ is shown. The power control system600′″ includes a wire harness720, which includes two sets of main power supply wires622and main power return wires624for routing one of the heaters (i.e., the fourth heater656) as a stand-alone heater, and the remaining ones of the heaters (i.e., the first, second and third heaters650,652,654) in a series connection. The first, second and third heaters650,652,654are connected in series in this order to form a sixth modular heater assembly. In the sixth modular heater assembly, the second heater652is the master control heater whose thermocouple junction635and temperature sensing wire632′ 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 wire622and main power return wire624are connected to the sixth modular heater assembly. The second set of main power supply wire622and the main power return wire624connect only the fourth heater656to the controller610such that the fourth heater becomes a stand-alone heater.

Three connectors and six auxiliary wires are used for connecting the second heater652to the controller610, to the first heater650, and the third heater654. Two connectors and five auxiliary wires are used for connecting each of the first heater650and the third heater654to another heater. Two connectors and five auxiliary wires are used for connecting the fourth heater656to the controller610. Each set of the auxiliary wires for the first heater650, the third heater654and the fourth heater656includes five wires, including a temperature sensing wire632′, an auxiliary power supply wire634′, an auxiliary power return wire636′, a first routing wire660, and a second routing wire662, similar to that ofFIG.27. However, the set of auxiliary wires for the second heater652, which is used as the main control heater, includes six wires. The six wires include a temperature sensing wire632′, an auxiliary power supply wire634′, and four routing wires664. All of the six wires are used in each mode of heater operation.

In the present form, the thermocouple junction635for the second heater652is formed between the temperature sensing wire632′ and the resistive heating element637. The thermocouple junctions635for the first and third heaters650,654are formed between the temperature sensing wires632′, the auxiliary power supply wires634′, and the resistive heating elements637. The thermocouple junction635for the fourth heater656is formed between the temperature sensing wire632′, the auxiliary power return wire636′, and the resistive heating element637. All of the temperature sensing wires632′ and the two main power return wires624are made of the first conductive material (Material A, such as Constantan), whereas the remaining wires (including the two main power supply wires622, the connecting wires640connecting to the same or adjacent connectors, the auxiliary power supply wires634′, the auxiliary power return wires636′ and the routing wires660,662) are made of a second conductive material (Material B, such as Chromel®).

In summary, the power control system600,600′,600″, or600′″ constructed in accordance with the teachings of the present disclosure include a wire harness612,612′,612″,720,722, or724that 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.