Patent Publication Number: US-8115147-B2

Title: Induction heating system output control based on induction heating device

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to induction heating and, particularly, to a system for controlling the output of an induction heating power source based on the induction heating device coupled to the induction heating power source. 
     Induction heating is a method of heating that utilizes a varying magnetic field to heat a work piece. This varying magnetic field is produced by transmitting an alternating current through an induction heating device. A work piece located inside or in close proximity to the induction heating device is exposed to the varying magnetic field, inducing movement of electrons and causing a flow of eddy currents within the work piece. These eddy currents and resistance to current flow within the work piece cause the temperature of the work piece to rise. Thus, the amount of heat induced in the work piece may be controlled by changing the magnetic field strength as a result of varying the amount of alternating current flowing through the induction heating device. 
     An induction heating system typically comprises an induction heating power source and an induction heating device that is coupled to the induction heating power source. Again, alternating electrical current flowing from the induction heating power source and through the induction device produces the varying magnetic field. In traditional induction heating systems, several different kinds of induction heating devices may be coupled to the same induction heating power source. For example, a given induction heating power source may supply power to an air-cooled induction heating device or, alternatively, a liquid-cooled induction heating device, for example. 
     Different induction heating devices, however, present different operating limits. That is, certain operating parameters that may be appropriate for one kind of induction device may lead to damage of a second kind of induction device. Indeed, different induction heating devices may have varying limits with respect to the amount of electrical current that may flow through the given induction heating device before damage is a concern. Thus, although the same induction heating power source may be used to operate these different induction heating devices, the induction heating power source may be operable to produce an output undesirable to the coupled induction heating device, potentially causing damage to the induction heating device. Therefore, a technique to mitigate the likelihood of the operating limits of an induction heating device from being exceeded is desirable. 
     SUMMARY OF THE INVENTION 
     In accordance with certain exemplary embodiments, the present invention provides systems and methods for inductively heating a work piece. In one exemplary embodiment, the induction heating system includes an induction heating power source. The induction heating power source is operable to identify the type of induction heating device coupled to the induction heating power source. Additionally, the induction heating power source is operable to automatically impose limits on the output parameters to the induction heating device based on the identity of the induction heating device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: 
         FIG. 1  is a diagrammatic illustration of an induction heating system, according to an exemplary embodiment of the present technique; 
         FIG. 2  is a diagram of the process of inducing heat in a work piece using a varying magnetic field, according to an exemplary embodiment of the present technique; 
         FIGS. 3   a ,  3   b ,  3   c , and  3   d  are elevation views of a rear portion of the induction heating system of  FIG. 1 ,  FIG. 3   a  illustrating a pair of power source output connectors,  FIG. 3   b  illustrating the pair of power source output connectors with a protective cover on one connector,  FIG. 3   c  illustrating a pair of fluid-cooled extension cables coupled to the power source output connectors, and  FIG. 3   d  illustrating a pair of air-cooled extension cables coupled to the power source output connectors; 
         FIG. 4  is an elevation view of a work piece and a plurality of temperature feedback devices disposed on the work piece, according to an exemplary embodiment of the present technique; 
         FIG. 5  is an elevation view of the control panel of the induction heating system of  FIG. 1 , according to an exemplary embodiment of the present technique; 
         FIG. 6  is a schematic diagram of a temperature controller, according to an exemplary embodiment of the present technique; 
         FIG. 7  is a schematic diagram of a power source controller, according to an exemplary embodiment of the present technique; 
         FIG. 8  is a schematic diagram of the induction heating system, according to an exemplary embodiment of the present technique; 
         FIG. 9  is an elevation view of an induction heating power source connector and an induction heating fluid-cooled extension cable connector, according to an exemplary embodiment of the present technique; 
         FIG. 10  is a front elevation view of the induction heating power source connector of  FIG. 9 ; 
         FIG. 11  is a front elevation view of the induction heating fluid-cooled extension cable connector of  FIG. 9 ; 
         FIG. 12  is an elevation view of an induction heating air-cooled extension cable connector, according to an exemplary embodiment of the present technique; 
         FIG. 13  is a front elevation view of the air-cooled induction heating extension cable connector of  FIG. 12 ; 
         FIG. 14  illustrates a liquid-cooled extension cable, according to an exemplary embodiment of the present technique; 
         FIG. 15  illustrates a liquid-cooled induction heating device, according to an exemplary embodiment of the present technique; 
         FIG. 16  illustrates an air-cooled extension cable, according to an exemplary embodiment of the present technique. 
         FIG. 17  illustrates an air-cooled heating blanket, according to an exemplary embodiment of the present technique; and 
         FIG. 18  illustrates an air-cooled induction heating cable, according to an exemplary embodiment of the present technique. 
     
    
    
     DETAILED DESCRIPTION 
     Referring generally to  FIG. 1 , a system  20  for inductively heating a work piece  22  is illustrated. In  FIG. 1 , the work piece  22  is a pipe comprising two circular pipe sections welded together and surrounded by a protective thermal blanket  38 . However, it is worth noting that the induction heating system  20  is operable to inductively heat a variety of different work pieces. In the illustrated embodiment, the induction heating system  20  comprises an induction heating power source  24 , a fluid cooling unit  36 , a fluid-cooled extension cable  25 , and a fluid-cooled induction heating cable  26 . The fluid-cooled induction heating cable  26  is flexible to enable the fluid-cooled induction heating cable  26  to be wrapped around the work piece  22  to form a coil. Alternatively, the induction heating system  20  may comprise an induction heating power source  24 , an air-cooled extension cable, and an air-cooled induction heating cable or an air-cooled induction heating blanket, which are discussed further below. (See  FIGS. 16-18 ). 
     As illustrated in  FIG. 2 , the induction heating power source  24  is operable to produce an alternating electrical current  28  that is conducted through the fluid-cooled extension cable  25  to the fluid-cooled induction heating cable  26 . The alternating electrical current  28  flowing through the fluid-cooled induction heating cable  26  produces a varying magnetic field  30  that induces a flow of eddy currents  32  in the work piece  22  and that, in turn, heats the work piece  22 . Accordingly, controlling the level of the alternating electrical current from the induction heating power source  24  changes the strength of the magnetic field, thereby controlling the amount of heat generated in the work piece  22 . 
     Referring generally to  FIGS. 3   a ,  3   b ,  3   c  and  3   d , these figures respectively illustrate an induction heating power source  24  with no connectors mated, with a protective plug disposed thereon, with fluid-cooled extension cables coupled thereto, and with air-cooled extension cables coupled thereto. Again, the extension cables (air or fluid-cooled) facilitate coupling of the induction heating power source  24  and induction heating device. As illustrated in  FIG. 3   c , each of the fluid-cooled extension cables  25  has a connector  42  that is connected to a corresponding connector  44  on the induction heating power source  24 . The connectors  42  conduct electricity from the power source  24  to the fluid-cooled extension cables  25 . External to the connectors  42 , cooling fluid from the fluid cooling unit  36  is provided to the fluid-cooled induction heating cable  26  via hoses  46 . The connectors  44  also enable an air-cooled induction extension cable to be connected to the induction heating power source  24 . As will be discussed in more detail below, the induction heating power source  24  is operable to identify each type of extension cable connected to each connector  44 . In addition, the induction heating power source  24  limits the output power of the induction heating power source  24  based on the types of extension cable connected to the connectors  44 . In one embodiment, as shown in  FIG. 3   b , a protective plug  48  is provided to cover an unused connector  44 . The induction heating power source  24  is also able to identify when a cover  48  is placed over a connector  44 . 
     Referring generally to  FIGS. 1 and 4 , the induction heating system  20  is operable to receive temperature feedback from a plurality of temperature feedback sensors  50 , such as thermocouples, resistance temperature detectors (RTD&#39;s), or infrared sensors. These temperature feedback sensors  50  facilitate heating of the work piece  22  to a desired temperature and/or at a desired rate of temperature change. The exemplary thermocouples  50  are secured to the work piece  22  by spot welding and are coupled to the induction heating power source  24  by a thermocouple extension cable  52 . As illustrated, the thermocouples are located about and proximate to a weld joint “W” extending circumferentially around the work piece  22 . 
     Referring generally to  FIG. 5 , the illustrated induction heating power source  24  has a control panel  54  that enables a user to program the induction heating power source  24  to perform a variety of heating operations. For example, the control panel  54  may be used to program the induction heating power source  24  to heat the work piece  22  at a desired heat-up rate. In addition, the induction heating power source  24  may be programmed to maintain the work piece  22  at an elevated temperature for a desired period of time. The induction heating power source  24  may also be programmed to reduce the work piece temperature from an elevated temperature at a desired cool-down rate. It is worth noting that a number of operating programs having varied heating profiles are envisaged, and the foregoing techniques are merely examples. 
     To facilitate controlled operations of the induction heating power source  24  and the magnetic field created by the induction heating device  26 , the exemplary embodiment includes the control panel  54 , as discussed above. This control panel  54  has four temperature displays  56 , one for each of four thermocouples  50  operable to control operation of the induction heating power source  24 . The exemplary control panel  54  also has four control lights  58 , one for each of the thermocouples  50  used to control temperature, to indicate which of the four control thermocouples  50  is controlling the operation of the system  20  at that point in time. In addition, the illustrated control panel  54  has a main display  60  to facilitate the programming of the induction heating power source  24  and for monitoring system parameters, such as the output power, output voltage and current and output frequency. Additionally, the display  60  is capable of providing program status information as well as diagnostic information should a problem arise. In this embodiment, the control panel  54  has a cursor button  62  that may be used in cooperation with the main display  60  to program the induction heating power source  24 . In addition, the illustrated control panel  54  has an up arrow button  64  and a down arrow button  66  to enable a user to input data, such as a desired heat-up rate, a desired temperature, a desired time, and a desired cool-down rate. 
     The illustrated control panel  54  also has a run button  68 , a hold button  70 , and a stop button  72  that may be used to control the operation of the induction heating system  20 . The run button  68  enables a user to initiate operation of the induction heating system  20 . The hold button  70  enables a user to pause operation of the induction heating system  20  temporarily and maintain workpiece temperature. Operation restart of the induction heating system  20  in accordance with the programming instructions is achieved by pressing the run button  68 . The stop button  72  halts operation of the system  20  completely. The control panel  54  may also have a light  74  to provide an indication to a user that a fault condition exists. Another light  76  may be provided to indicate to a user when an operating limit, such as output voltage or current, has been reached. Finally, a light  78  may be provided to indicate when power is being applied to the induction heating cables  26 . 
     Referring generally to  FIG. 6 , the induction heating power source  24  has a temperature control circuit  80  that includes a thermocouple interface board  81  and the control panel  54  for operator interface. The temperature control circuit  80  utilizes a processor  82 , located on the operator interface  54 , to direct operation of the induction heating system  20  in response to programming instructions received from the control panel  54  and temperature data received from the thermocouples  50  connected to the thermocouple interface board  81 . The illustrated induction heating system  20  has six thermocouple inputs  84  to enable each of the six thermocouples  50  to be connected to the induction heating power source  24 . Each of the thermocouple inputs  84  is coupled to an analog-to-digital converter (ADC)  86  that converts the analog temperature data from the thermocouples  50  into a digital temperature signal. Each ADC  86  is coupled to an optoisolator  88 . Each optoisolator  88  couples the digital temperature signal from an ADC  86  to the processor  82  while maintaining electrical isolation of the processor  82  from each ADC  86 . It is worth noting that multi-channel optoisolators are envisaged as well. 
     In this embodiment, the processor  82  receives digital temperature data from each ADC  86  sequentially. A number of circuit paths are provided to enable the processor  82  to communicate with each ADC  86  and a decoder  92 . A first signal bus  90  is provided to couple the digital temperature data from each of ADC  86  to the processor  82 . The decoder  92  is provided to control each ADC  86  to transmit the digital temperature data sequentially to the processor  82 . A second signal bus  94  is provided to couple the decoder  92  to each ADC  86 . A third signal bus  96  is provided to enable the processor  82  to communicate to each ADC  86 . Each ADC  86  transmits its temperature data to the processor  82  when queued by the decoder  92  and the processor  82 . A fourth signal bus  98  is provided to transmit calibration data to each ADC  86 . A digital-to-analog converter (DAC)  100  is provided to couple the temperature data to a chart recorder via a chart recorder interface  102 . In addition, a memory device  104  is provided to store calibration data. 
     The processor  82  is operable to receive programming instructions from the various programming buttons  106  disposed on the control panel  54 . However, other methods of programming the processor  82  may be used. The programming buttons  106  comprises the cursor button,  62 , the up arrow button,  64 , the down arrow button,  66 , the run button  68 , the hold button,  70 , the stop button  72 , etc. The processor  82  may also provide signals to the temperature displays  56  and the main display  60 . The processor  82  produces an output signal that is coupled to a power source controller interface  108 . 
     Referring generally to  FIG. 7 , the power source controller interface  108  couples the control signal from the temperature controller circuit  80  to an induction heating power source controller  110 . The induction heating power source controller  110  has a processor  112  that provides a command signal  114  that controls the output of the induction heating power unit based on the control signal received from the processor  82  in the temperature controller circuit  80 . The processor  112  also receives inputs from a multiplexer  116 . As will be discussed in more detail below, the multiplexer  116  receives a thermocouple input  123  from the fluid cooling unit  36  and thermistor inputs  143 ,  145 , and  147  from a plurality of thermistors  142 ,  144  and  148 , respectively, disposed within the induction heating power source  24  (see  FIG. 8 ). In addition, the multiplexer  116  receives an identifier signal  120   a  or  120   b  representative of the type of induction heating extension cable employed from the induction heating power source connectors  44  illustrated in  FIGS. 3   a - 3   d . Each type of induction heating extension cable (air-cooled or fluid-cooled) that may be connected to the induction heating power source  24  has its own unique identifier. The processor  112  is programmed to adjust or limit power to the induction heating device based on its type. Additionally, the processor  112  is programmed to not permit operation if the induction heating device types are different or if an unused output connection does not have a protective plug in place to signify it as an unused connection. In addition to control based on input from temperature control circuit  80 , the power source controller  110  is operable to control power from the induction heating power source  24  based on the heatsink thermistor inputs  143 ,  145  and  147 , the extension cable connector identifier inputs  120   a  or  120   b , and the coolant temperature input  123 . 
     Referring generally to  FIG. 8 , an electrical schematic of the induction heating system  20  is illustrated. The temperature controller  80  receives the temperature feedback from the plurality of temperature feedback devices  50 . The temperature controller  80  compares the actual temperature of the work piece  22 , represented by the temperature feedback, to a desired temperature based on programming instructions stored in the temperature controller  80 . The temperature controller  80  provides a signal  108  to the power source controller  110  that is representative of a desired output of the induction heating power source  24  to make the actual temperature of the work piece  22  equal to the desired temperature. The power source controller  110  controls the operation of the induction heating power source  24  to provide the desired output. As will be discussed in more detail below, the power source controller  110  controls the output of the induction heating power source  24  by controlling the opening and closing of electronic switches in a pair of inverter circuits. By selectively increasing or decreasing the frequency that the electronic switches  130  are opened and closed, the output of the induction heating power source  24  may be increased or decreased as desired. 
     In the illustrated embodiment three-phase AC input power is coupled to the induction heating power source  24 . A rectifier  124  is used to convert the AC power into DC power. A filter  126  is used to condition the rectified DC power signals. A first inverter circuit  128  is used to invert the DC power into desired AC output power. In the illustrated embodiment, the first inverter circuit  128  comprises a plurality of electronic switches  130 , such as IGBTs. The electronic switches  130  are opened and closed by command signals  114  from the power source controller  110 . The power source controller  110  controls the operation of the electronic switches  130  to provide the desired output of the induction heating power source  24 . A step-down transformer  132  is used to couple the AC output from the first inverter circuit  128  to a second rectifier circuit  134 , where the AC is converted again to DC. An inductor  136  is used to smooth the rectified DC output from the second rectifier  134 . The output of the second rectifier  134  is coupled to a second inverter circuit  138 . The second inverter circuit  138  converts the DC output into high-frequency AC signals. The electronic switches  130  of the second inverter circuit  138  also are opened and closed by command signals  114  from the power source controller  110 . The power source controller  110  controls the operation of the electronic switches  130  to provide the desired output of the induction heating power source. A tank capacitor  140  is coupled in parallel with the output connectors  44 . As illustrated, the fluid-cooled induction heating cable  26  is connected to connectors  44 . However, an air-cooled induction heating device may be coupled to connectors  44 . 
     The coiled fluid-cooled induction heating cable  26  is represented on the schematic as an inductor. The inductance of the induction heating cable  26  and the tank capacitor  140  form a resonant tank circuit. The inductance and capacitance of the resonant tank circuit establishes the frequency of the AC current flowing through the fluid-cooled induction heating cable  26 . The inductance of the fluid-cooled induction heating cable  26  is influenced by the number of turns of the induction heating cable  26  around the work piece  22 . As discussed above, the current flowing through the fluid-cooled induction heating cable  26  produces the magnetic field that induces eddy current flow, and, thus, heat in the work piece  22 . 
     A large amount of electrical current may flow through the various components of the induction heating power source  24  and the induction heating cable  26 . This current produces heat within the power source  24  that may damage the components. Solid-state components, such as the IGBTs  130  and the rectifiers, are particularly susceptible to heat damage. In the illustrated embodiment, the power source  24  is adapted to control output power to prevent heat damage to certain components. One or more temperature feed back devices, such as thermistor, are disposed within the induction heating power source  24  to provide temperature signals to the power source controller  110 . A thermistor  142  is disposed adjacent to the first inverter  128  to provide a signal representative of the temperature of the first inverter  128  to the power source controller  110 . Another thermistor  144  is disposed adjacent to the second inverter  138  to provide a signal representative of the temperature of the second inverter  138  to the power source controller  110 . Yet another thermistor  148  is provided to provide a signal representative of the temperature of the rectifier  134  to the power source controller  110 . 
     In addition to the signal  108  from the temperature controller  80  that is representative of a desired output of the induction heating power source  24 , the power source controller  110  also receives signals from other sources that are used to control the output of the induction heating power source  24 . For example, temperature signals from the first thermistor  142 , the second thermistor  144 , the third thermistor  148 , and a coolant temperature signal  123  from the fluid-cooling unit (illustrated in  FIG. 7 ), and an identifier signal  120   a  or  120   b  representative of the type of induction heating extension cable connected to the induction heating power source  24  are provided to the power source controller  110 . The power source controller  110  receives a command signal from the temperature controller  80  to produce a desired output. However, if any of the parameters of the desired output are above the limits for the induction heating device connected to the induction heating power source  24 , the power source controller  110  limits output power to the limits for the specific induction heating device. Similarly, if the temperature signals from thermistors  142 ,  144 ,  148  from the various induction heating system components is above a setpoint, or coolant temperature feedback is above a setpoint, the power source controller  110  limits or reduces power from the induction heating power source  24 . However, a variety of control schemes may be used to control the output of the induction heating power source  24  based on the temperature signals from the induction heating system components and the type of induction heating devices connected to the induction heating power source  24 . The foregoing are merely examples of control schemes, and a host of various control schemes are envisaged, although not discussed for clarity. Indeed, the system may be responsive to any combination or permutation of inputs from the signal producing devices, such as thermistors or the thermocouples, for instance, located throughout the system. 
     As noted above, the power source controller  110  is programmed to limit the signal  108  from the temperature controller  80  so that the induction heating power source  24  is not driven to produce additional power when a specified induction heating system component temperature is reached. The power source controller  110  is also programmed to reduce the amount of power produced by the induction heating power source  24  when a specified induction heating system component temperature limit threshold is reached. Additionally, the power source controller  110  is programmed to stop operation of the induction heating power source  24  if a specified component maximum temperature threshold is reached or exceeded. Limiting or reducing the desired output of the induction heating power source  24  reduces the amount of heat produced within the system  20 , thereby, protecting induction heating system components from heat damage. 
     In addition, as noted above, the power source controller  110  is programmed to automatically limit the output power from the induction heating power source  24  based on the specific induction heating extension cable connected to the induction heating power source  24 . In the illustrated embodiment, two different kinds of induction heating extension cables  25  may be electrically coupled to the induction heating power source  24 . For example, a fluid-cooled induction heating extension cable or an air-cooled induction heating extension cable may be coupled to the induction heating power source  24 . To prevent damage, when multiple extension cables are connected, the induction heating extension cables must be of the same type, or the power source will not deliver output. Each of these induction heating extension cables is operable to provide a signal representative of the specific type to the induction heating power source  24 . Thus, the induction heating system intelligently determines appropriate output power or if power should be provided at all. As will be explained in more detail, the fluid-cooled extension cable is designed to accommodate only fluid-cooled induction heating devices and the air-cooled extension cable is designed to accommodate only air-cooled induction heating devices. 
     Referring generally to  FIGS. 9-11 , a fluid-cooled induction heating extension cable  25  may be connected to the induction heating power source  24 . The illustrated fluid-cooled induction heating extension cable connector  42  has a pair of fluid connectors  152  for coupling cooling fluid to and from the fluid-cooled induction heating extension cable  25 . In addition, the fluid-cooled induction heating extension cable connector  42  has a pair of high power contacts  154  that are inserted into a corresponding pair of high power contacts  156  on the induction heating power source connector  44  to couple power from the induction heating power source  24  to the fluid-cooled induction heating extension cable  25 . The induction heating extension cable connector  42  also has a second pair of low power contacts  158 . An electrical resistor  160  housed within the connector  42  is connected between the two low power contacts  158  and serves as an identifier for the fluid-cooled induction heating extension cable  25 . In addition, the induction heating power source connector  44  has a second pair of low power contacts  162  that receive the two low power contacts  158  when the fluid-cooled induction heating extension cable connector  42  is connected to the induction heating power source connector  44 . The second pair of low power contacts  162  couple the resistance of the electrical resistor  160 , i.e., the source of the identifier  120   a  or  120   b , to the power source controller  110  of  FIGS. 7 and 8  via lead  164 . The power source controller  110  receives the unique identifier  120   a  or  120   b  from the fluid-cooled induction heating extension cable  25  and limits the output of the induction heating power source  24  based on the unique identifier. The value of the electrical resistance of the electrical resistor  160  may correspond to the operating limit of the induction heating device. 
     Referring generally to  FIGS. 12 and 13 , an air-cooled induction heating extension cable connector  166  is illustrated. The air-cooled induction heating extension cable connector  166  also has a resistor  168  coupled between a pair of identifier contacts  158 . However, the value of the electrical resistance of the resistor  168  in the air-cooled induction heating extension cable connector  166  is different than the value of the electrical resistance of the resistor  160  in the fluid-cooled induction heating extension cable connector  42 . The unique resistance signal  120   a  and  120   b  is transmitted from the air-cooled induction heating extension cable connector  166  to the power source controller  110  of  FIG. 8 . The power source controller  110  of  FIG. 8  receives the unique resistance signal  120   a  or  120   b  and limits the output of the induction heating power source to a second operational limit. Thus, the induction heating power source  24  is operable to limit output of the induction heating power source  24  specifically for each induction heating device electrically coupled to the induction heating power source  24 . 
     Turning to  FIG. 14 , this figure illustrates the heating device end of a liquid-cooled extension cable  25   a . As illustrated, the device end is located opposite the end of the liquid-cooled extension cable  25   a  that is proximately coupled to the controller  54  and power source  24 , and cooling unit  36 . The device end of the liquid-cooled extension cable  25  includes a pair of male connectors  170   a , and these male connectors  170   a  are configured to engage with corresponding female connectors  180   a  of the liquid-cooled induction heating cable  26   a  illustrated in  FIG. 15 . In the illustrated embodiment, the male connectors  170   a  and the female connectors  180   a  are configured such that only appropriately corresponding extension cables and induction heating cables may be coupled to one another. That is, as is illustrated in  FIGS. 14 and 15 , the male connectors  170   a  and the female connectors  180   a  ensure that only a liquid-cooled induction heating cable  26   a  may be coupled to the liquid-cooled extension cable  25   a . Thus, the output parameters of the induction system  20  are limited for effective operation of the liquid cooled induction heating cable  26   a.    
     Similarly, the air-cooled extension cable  25   b  illustrated in  FIG. 16  includes female connectors  170   b  that are configured to mate with corresponding male connectors  180   b  of the air-cooled induction heating blanket  26   b  of  FIG. 17 , or with male connectors  180   c  of the air-cooled induction heating cable  26   c  of  FIG. 18 . These connectors  170   b ,  180   b , and  180   c  are constructed in such a manner as to ensure that only air-cooled induction heating devices (e.g., air-cooled heating blanket  26   b  and air-cooled induction heating cable  26   c ) can be coupled to the air-cooled extension cable  25   b . Moreover, the configuration specific genders of the extension cables and induction devices ensure that an air-cooled extension cable  25   b  is not inadvertently coupled to a liquid-cooled induction device, and vice-versa. Thus, the likelihood of damage due to operation of the induction device outside desired operating parameters is reduced. 
     The techniques described above provide a system  20  and a method for inductively heating a work piece  22 . In addition, the techniques protects induction heating devices used with the system  20  from damage by limiting the amount of power that may be applied to the induction heating devices based on the type of induction heating device used. In addition, the system  20  performs the identification of the induction heating device automatically. 
     While the invention may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.