CONTROL OF ELECTRONIC HEATERS

A system, and related method, employable with an electronic heater that includes, in one embodiment, a power converter coupled to the electronic heater via a disconnect switch configured to conduct to deliver an output voltage produced by the power converter to the electronic heater to control a temperature thereof. The system also includes a current source coupled across the electronic heater, and a power converter controller configured to adjust the output voltage produced by the power converter responsive to a test current produced by the current source when the disconnect switch is not conducting.

FIELD OF THE INVENTION

The present invention is directed in general to power electronics and, more specifically, to power control of electronic heaters.

BACKGROUND

Electrically powered heater elements (of electronic heaters) are utilized in many manufacturing processes including semiconductor wafer processing, metal treatment, chemical processes, etc. Accurate control of delivered heat and an achieved temperature is often a requirement. Historically heat is measured independently of electrical power delivery, requiring an additional measurement apparatus and controllers to regulate a delivered temperature. Oftentimes this additional equipment can cause problems due to size, cost, and system accessibility constraints.

To produce a requisite level of temperature in a host system, electrical power is delivered to a resistive heating element of the electronic heater thermally coupled to the host system. The electronic heater is powered by a variable output, controllable, electrical power source (a power converter). The variable output of the power converter is controlled via a feedback loop that receives temperature data from temperature sensors located on or near the electronic heater, and a control input from the host system. The feedback loop is designed to provide the desired precision and timing required by the process. It is not uncommon in some system arrangements for temperature to be controlled within one degree Celsius (on the order of 0.1 percent (“%”)) of a setpoint, along with temperature update rates on the order of fractions of a second.

Temperature sensors in such arrangements are typically realized with thermocouples, resistive temperature measuring devices, bimetallic devices, change-of-state sensors, or infrared pyrometers. Electrical connections to these temperature sensors must be routed from the electronic heater back to a controller, and these connections can sometimes add significantly to overall system complexity. For example, if the electronic heater is in a vacuum chamber, any chamber penetrations require special seals to prevent air leakage. Likewise, if the chamber includes elevated levels of radio frequency (“RF”) energy as is sometimes the case in semiconductor processing, any chamber penetration must be carefully filtered to prevent RF leakage.

As introduced herein, a temperature in a host system produced by an electronic heater is automatically monitored and controlled via heater power connections. The heater power connections employ a temperature sensing arrangement that can eliminate a need for additional apparatus and cost, thereby providing a simplified system structure.

SUMMARY

These and other problems are generally solved or circumvented, and technical advantages are generally achieved, by advantageous embodiments of the present invention. In one embodiment, a system, and related method, is employable with an electronic heater and includes a power converter coupled to the electronic heater via a disconnect switch configured to conduct to deliver an output voltage produced by the power converter to the electronic heater to control a temperature thereof. The system also includes a current source coupled across the electronic heater, and a power converter controller configured to adjust the output voltage produced by the power converter responsive to a test current produced by the current source when the disconnect switch is not conducting.

Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated, and will not be redescribed in the interest of brevity after the first instance. The FIGUREs are drawn to illustrate the relevant aspects of exemplary embodiments.

DETAILED DESCRIPTION

The making and using of the present exemplary embodiments are discussed in detail below. It should be appreciated, however, that the embodiments provide many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the systems, subsystems, and modules associated with a system and method for controlling a temperature of electronic heaters in a host system.

A system will be described herein with respect to exemplary embodiments in a specific context, namely, a system for accurately controlling a temperature of an electronic heater (i.e., an electrically powered heater) in a host system. The specific embodiments include, but are not limited to employing a variable output power source (a power converter) to elevate the temperature in the host system. The principles of the present invention are applicable to other temperature management systems that are configured to elevate a temperature in the host system with a variable output power source.

An objective of the present disclosure is to accurately and controllably elevate the temperature in the host system employing an electronic heater. The elevated temperature of the electronic heater is automatically and accurately monitored via heater power configurations without introducing an unnecessary cost. The process and method utilize multiple electronic heaters sharing common conductors, and is able to provide near real-time digital control. Highly precise remote heater element measurements can be produced. Control utilizes heater power configurations for both delivery of power and monitoring of temperature.

Turning now toFIG.1, illustrated is a block diagram of an embodiment of a power system100formed with a plurality of power converters (designated “PC1, PC2”)105,110controlled by a power converter controller115. The power converters105,110may comprise like or different power converter topologies. Also, ones of the power converters105,110may be positioned at different locations. While only two power converters105,110are illustrated, the power system100can include additional power converters depending on the application.

The power converter controller115includes a processor120(e.g., a microprocessor), an analog-to-digital converter/digital-to analog converter (“ADC/DAC”)125and a communications gateway (designated “COMM G/W”)130. The power converter controller115includes local interfaces such as a display135(e.g., a touch screen display). The local interfaces may also include a first communications interface (designated “COMM I/F1”)140such as a USB interface for communications with an external device. The local interfaces may also include a second communications interface (designated “COMM I/F2”)145such as secure digital (“SD”) interface for, without limitation, inputting control parameters for the power system100, updating firmware of the power converter controller115, and/or logging power system data. Of course, the power converter controller115may include additional local interfaces depending on the application. For instance, the power converter controller115may include an input power interface (designated “PIN I/F”)147to provide input power thereto from a power bus (e.g., a 24 volt power bus). The input power interface147can communicate a status and/or an operational condition of power-related items such as circuit breakers, disconnect contactors, power monitors, etc.

The power system100powers a host system150. The host system150includes a plurality of system elements (designated “SYSEL1, SYSEL2”)155,160and a host system controller165. While only two system elements155,160are illustrated, the host system100can include additional system elements depending on the application. The host system150is coupled to a remote system170via a communication path172. Of course, the host system150may be coupled to additional remote systems depending on the application.

The power converter controller115can communicate with the host system150over a plurality of buses. The power converter controller115can communicate with the host system150using a host system protocol over the plurality of buses. For instance, the host system150can provide host system signals including status information about the system elements and control command information to the power converter controller115over a discrete analog bus167and/or a serial digital bus168. The host system signals may include discrete, real-time, analog and/or digital input signals and output signals. Conversely, the power converter controller115can provide power system signals including status and control information to the host system150with respect to the system elements155,160over the discrete analog bus167and/or the serial digital bus168. The power system signals may include, without limitation, power system output voltage, output current, temperature and/or status of the input power, as well as other power or host system monitoring information. The discrete analog bus167and/or the serial digital bus168are coupled to the ADC/DAC125of the power converter controller115.

Additionally, the host system150can provide host system signals including status and control information with respect to the host system controller165to the power converter controller115over a controller bus169(e.g., a serial digital bus). Conversely, the power converter controller115can provide power system signals including status and control information to the host system150with respect to the host system controller165over the controller bus169. The power system signals may include, without limitation, power system output voltage, output current, temperature and/or status of the input power, as well as other power or host system monitoring information. The controller bus169is coupled to the communications gateway130of the power converter controller115. Of course, the power converter controller115and host system150may communication over additional buses depending on the application.

The controller bus169can be utilized for near-real-time control of delivered power to the host system150to provide desired host system functionality. For example, the host system150may employ electronic heaters, where power to the heaters controls process temperature and this temperature can be varied to achieve desired results. There are many other examples where near-real-time control and reporting on delivered power would be beneficial to the host system150. Another important consideration is host system control latency such as the delay between where a command is issued and where the power system100provides the desired response, or the delay between where the power system100delivers a command and when the power system reports the command to the host system controller165. Modern host systems150often demand command and reporting latency as low as, for instance, one to five milliseconds for desired performance. The design of the power converter controller115takes into account these requirements. The power converter controller115(via, for instance, the communications gateway130) can provide control and communications latency of less than five milliseconds (e.g., beneficially less than one millisecond). In an embodiment, a time response of a temperature to a command is modeled to more accurately and more quickly control the time response of a temperature of the host system.

The power converter controller115controls the power converters105,110via buses such as serial digital buses107,112, respectively. The power converters105,110provide power (designated “POUT1, POUT2, respectively) to the system elements155,160of the host system150.

The power converter controller115provides a status of and controls the power converters100,110and at least one system element155,160of the host system150responsive to the host system signals. The control may include a scripted sequence of events from the processor120as a function of a change of an operational condition of at least one of the power converters105,110and the host system150. The status of the power converters105,110and at least one system element155,160of the host system150may be displayed on the display135. In addition to monitoring at least one system element155,160of the host system150, the power converter controller115can monitor a status of and control the remote system170as well.

As an example, the power system controller115can provide a scripted sequence of events (or responses) related to a safety system (a system element155,160or remote system170) associated with the host system150. The scripted sequence of events can be related to, for example, an emergency power cutoff contactor (a system element155,160or remote system170) that cuts off power to the host system150, as well as interlocks (a system element155,160or remote system170) that are outside the power system100. Host system signals (that apply to the system elements155,160and remote systems170) can be routed to the power converter controller115for the scripted sequence of events to control the power converters105,110, the host system150and/or the remote system170. As further examples, the system element155,160may include, without limitation, a leak detector, and/or a temperature sensor that can be controlled by the power converter controller115.

Thus, the power converter controller115can be configured to operate as a central control point for power and system management. As non-limiting examples, other system sensor signals such as air conditioner monitor signals, contactor status signals, general relay board status signals, and signals that can prevent the power system100from powering on can also be coupled to the power converter controller115employing an appropriate protocol.

Turning now toFIG.2, illustrated is a block diagram of an embodiment of portions of a power converter controller200of a power system (see, e.g.,FIG.1). As illustrated inFIG.2, a processor205(e.g., a microprocessor) is utilized as a communications and control hub. This includes communications with a host system via, for instance, Ethernet, CANbus, USB, or an isolated low voltage discrete signal (“LVDS”) serial peripheral interface bus (“SPIbus”). An LVDS SPIbus provides a fast, robust, and relatively noise-immune communication link. When an SPIbus is utilized, a third party communications bridge, such as the HMS Anybus product, can be implemented to support other host communication protocols, such as Ethernet, Ethercat, Profinet, CANbus, RS232, I2C, USB, or others.

Power system internal communications can be accomplished via CANbus to connected power converters, or via discrete digital and/or analog signals, as appropriate. Discrete input/output (“I/O”) ports can also be used for host system communication and control, as desired or needed. The processor205can also interface to a display215(e.g., a touch screen display) for local, manual control of the power system.

The processor205in conjunction with memory210(e.g., embedded memory such as electrically erasable programmable read-only memory (“EEPROM”)) provides real-time operating system control, as well as serving as a repository of various system control algorithms, wherein a plurality of power converters can be amalgamated into a single entity from control and reporting standpoints. Likewise, various operational scripts (scripted sequence of events or responses) can be implemented, such as controlling startup, shutdown, sequencing, control limits, as well as other parameters, of the power system and host system.

FIG.2illustrates example inputs and outputs of the power converter controller200demonstrating communication with, for instance, power system components, the host system, and remote systems. A display bus212(e.g., I2C external bus interface pan bus) provides communication with the display215. A first communications interface bus217provides communication with a first communications interface (designated “COMM I/F1”)220. For the example ofFIG.1, a USB bus (the first communications interface bus217) provides communication with a USB interface (the first communications interface215) for a USB device (an external device). A second communications interface bus222provides communication with a second communications interface (designated “COMM I/F2”)225. For the example ofFIG.1, an SD bus (the second communications interface bus222) provides communication with an SD interface (the second communications interface225) for an SD card.

An ADC/DAC bus227(e.g., an SPIbus) provides communication with an ADC/DAC230. A communications gateway bus232(e.g., a serial digital bus) provides communication with a communications gateway (designated “COMM G/W”)235. A power converter bus237(e.g., a serial digital bus, CANbus) provides communication with a power converter interface (designated “PC INTERFACE”)240. A host system bus242(e.g., a CANbus) provides communication with a host system interface245for, without limitation, system elements of the host system or a remote system. Of course, other buses and interfaces are well within the scope of the present disclosure.

Turning now toFIG.3, illustrated is a diagram of a system300to power an electronic heater320. A power converter310is coupled to the electronic heater320. The electronic heater320is thermally coupled to a component in the host system such as a resistive heating element. A temperature measurement sensor330senses the temperature of the component in the host system. The temperature measurement sensor330can be realized, without limitation, with a thermocouple, a resistive temperature sensing device, a bimetallic device, a change-of-state sensor, and/or an infrared pyrometer. A power converter controller (“PCC”)340receives a temperature control input signal350indicating the temperature to which the host system will be controlled. A power converter control signal360produced by the controller340is employed to control the variable output of the power converter310.

Turning now toFIG.4, illustrated is a diagram of a system400to power an electronic heater420. The system400utilizes heater power connections for temperature measurements for heater control. The system400utilizes a resistive temperature measuring device that has a known temperature-versus-resistance characteristic to determine the measured temperature. This principle can also be applied to the resistive electronic heater420. If the delivered voltage (“V”) and current (“I”) are monitored, the resistance (“Relement”) of the resistive temperature measuring device can be determined utilizing Ohm's Law as Relement=V/I.

As illustrated inFIG.4, real-time measurements of output voltage V and current I of a power converter410are fed back to a power converter controller (“PCC”)440. The circles with the letter “M” inFIG.4(and in later FIGUREs) symbolically represent measurement devices or sensors such as voltage or current measurement devices. The power converter controller440receives a temperature control input signal450indicating the temperature to which the host system will be controlled. The power converter controller440employs these measured values of voltage V or current I to compute heater resistance by dividing its voltage by its current. The heater resistance value is then compared to heater temperature versus resistance data to determine the heater temperature. A power converter control signal460produced by the power converter controller440is fed back to the power converter410, which adjusts its output voltage V to either increase or decrease power delivered to the electronic heater420to bring the temperature of the host system to the desired temperature.

While this system400can be quite effective at regulating heater temperature, there are some drawbacks that need to be considered. If power levels are high, the power converter410may generate electrical noise that can corrupt the fed-back values, thereby decreasing accuracy. Likewise, current measurements at higher output currents tend to be sensitive to transducer temperature drift, which decreases accuracy as power levels and time vary. If the power converter410operates with an ac output voltage (as opposed to a dc output voltage), monitoring of the root mean square (“RMS”) values of output current and voltage add complexity, potential errors and time delays to the system. If multiple power converters are utilized to power multiple electronic heaters, and these electronic heaters share a common return conductor, multiple currents flowing in the common return conductor can reduce accuracy of the heater resistance measurements, thereby decreasing sensed temperature accuracy.

Turning now toFIG.5, illustrated is a diagram of a system500to power first and second electronic heaters520,522. The system500utilizes a common return conductor570for powering a plurality of electronic heaters (the first and second electronic heaters)520,522. Power converter control signals550,552produced by the first and second power converter controllers (“PCC”)540,542are fed back to the first and second power converters510,512that adjust their output voltages V1, V2to either increase or decrease power delivered to the electronic heaters520,522to bring the temperature of the host system to the desired temperature (via temperature control input signals560,562). As illustrated inFIG.5, the two independent electronic heaters520,522share the common return conductor570back to their respective first and second power converters510,512. The output voltage V1monitored at the first power converter output then becomes (I1×RH1)+(I1+I2)×RRC, where I1is the current in the first electronic heater520, RH1is the resistance of the first electronic heater520, I2is the current in the second electronic heater522, and RRC is the resistance of the common return conductor570. The symbol “x” represents a multiply operation. The output voltage V2monitored at the second power converter output then becomes (I2×RH2)+(I1+I2)×RRC, where RH2is the resistance of the second electronic heater522.

If each electronic heater resistance is relatively modest (for example, less than 10 ohms) and power in each electronic heater520,522is relatively high (e.g., greater than 1000 watts (“W”)), then currents I1, I2will be on the order of 10 amperes (“A”) per electronic heater520,522. Likewise, if the resistance of the common return conductor570is on the order of 0.05 ohms, which is equivalent to a one volt voltage drop when conducting 20 A (power in the common return conductor570is 20 W, or about 1% of the total power delivered), the voltage drop on the common return conductor570will vary by 0.5 volts (“V”) as the currents I1, I2for each electronic heater520,522varies from 0 to 10 A. If the nominal voltage for each electronic heater520,522at 10 A is 100 V, a 0.5 V error in the measured voltage V1, V2translates to a 0.5% error, which can translate to a temperature error that is unacceptable in many applications. This effect is further amplified if additional electronic heaters share a common return conductor570.

Turning now toFIG.6, illustrated is a diagram of a system600to power first and second electronic heaters620,622. The system600avoids the effects of a common return conductor670on measured heater resistance values. A common return conductor670can be employed to provide a return power path for powering a plurality of electronic heaters (the first and second electronic heaters620,622). The two independent electronic heaters620,622share the common return conductor670back to their respective power converters610,612. Power converter control signals650,652produced by first and second power converter controllers (“PCC”)640,642are fed back to the power converters610,612that adjust their output voltages V1, V2to either increase or decrease power delivered to the first and second electronic heaters620,622to bring the temperature of the host system to the desired temperature (via temperature control input signals660,662).

As illustrated inFIG.6, each power converter610,612, includes a disconnect switch SwA_1, SwA_2(each under control of a respective switch controllers SwC1, SwC2) in series with its respective output. Also included are current sources CS_1, CS_2(each providing a test current Ip1, Ip2) coupled across the respective output of the power converters610,612. Illustrating a design example, the current sources CS_1, CS-2are constant current sources, which also may be varying currents. The current sources CS_1, CS-2may be configured as part of the power converters610,612, or can be connected external to the power converters610,612. These current sources CS_1, CS_2are utilized to implement a load resistance measurement process that avoids the effects of multiple heater currents in the common return conductor670. Accurate load resistance measurements enable accurate host temperatures to be determined.

The controller, collectively the first and second power converter controllers640,642, can provide an interrupt signal680that is routed respectively to both power converters610,612(to the respective switch controllers SwC1, SwC2). This interrupt signal680is configured to interrupt power flow from the first and second power converters610,612to the first and second electronic heaters620,622by turning OFF the respective disconnect switches SwA_1, SwA_2(via the respective switch controllers SwC1, SwC2) for a brief period of time and with a short duty cycle, typically on the order of 10%. The interrupt time is chosen so that thermal inertia in the host system produces an insignificant host system temperature change during this period of power interruption.

When power is interrupted, each power converter610,612is presented with the test current Ip1, Ip2. The output voltages V1, V2at the outputs of the power converters610,612are also measured during this period of power interruption so that resistance of each electronic heater620,622plus wiring connections is equal to Vheater/Ip (i.e., heater voltage divided by the respective test current Ip1, Ip2). Note that the heater voltage Vheater is equal to the output voltages V1, V2of the corresponding power converter610,612minus the voltage drop of the common return conductor670for each electronic heater620,622.

Resistance measurements are conducted with dc signals, regardless of the nature of the heater power signal. This simplifies the measurement methodology as RMS values need not be determined. While the common return conductor670will be carrying multiple test current signals during the measurement period, the test currents Ip1, Ip2typically do not vary very much, and any effects of these test currents Ip1, Ip2are accounted for during system calibration. Overall delivered power requirements from the power converters610,612are modestly increased by a factor of 1/DF, where DF is the duty cycle (also referred to as duty factor (“DF”)) of the interrupt signal680. For a DF of 0.9, delivered power increases by 11% (more precisely, 1/0.9) to maintain the power that would be delivered with no interruption.

Overall heater resistance measurement accuracy and precision will be dictated by the initial accuracy of the respective test current source CS_1, CS_2, the accuracy of the voltage measurement circuit, and effects of connection leads. These can be compensated for as part of an initial calibration procedure. Various options for control circuit implementation are available. As illustrated inFIG.6, the controller, collectively first and second power converter controllers640,642, can provide timing signals, calculate heater resistance RH1, RH2, and translate this to equivalent temperature values. The controller can control power flow for the electronic heaters620,622. The diodes D1, D2shown in series with the current sources CS_1, CS_2inFIG.6(and inFIGS.8and9) protect the current sources CS_1, CS_2from high voltages (e.g., voltages above (e.g., substantially) the regulated (controllable) output voltages V1, V2of the respective power converter510,512). This implementation assumes dc power for the electronic heaters620,622of a value that is greater than the bias voltage for the current sources CS_1, CS_2.

Turning now toFIG.7, illustrated are waveforms that show timing of the disconnect switches SwA_1, SwA_2ofFIG.6. The upper waveform illustrates the interrupt signal680and the other waveforms illustrate the current I1, I2in the first and second electronic heaters620,622, respectively. When the interrupt signal680is disabled from the controller, the disconnect switches SwA_1, SwA_2are ON (closed or conducting) under control of the respective switch controllers SwC1, SwC2, and the first and second electronic heaters620,622are ON powered by the respective first and second power converters610,612(see time intervals710). Conversely, when the interrupt signal680is enabled from the controller, the disconnect switches SwA_1, SwA_2are OFF (open or not conducting) under control of the respective switch controllers SwC1, SwC2, and the first and second electronic heaters620,622are operated at a reduced power level via the respective current sources CS_1, CS_2(see time intervals720). As mentioned above, the interrupt signal680is configured to interrupt power flow from the first and second power converters610,612to the first and second electronic heaters620,622, respectively, for a brief period of time and with a short duty cycle, typically on the order of 10%.

As illustrated inFIG.8, a central power converter controller (“PCC”)840of a system800can provide timing signals for a plurality of electronic heaters (“Electrical Heater Elements1,2, . . . n”, also “EHE1,2, . . . n”) powered by respective power converters (“Conv1,2, . . . n”). A common return conductor870can be employed to provide a return power path from the plurality of electronic heaters to the power converters. The components of the system800illustrated inFIG.8(andFIGS.9and10) are similar to those illustrated and described hereinabove with reference toFIG.6, and will not be redescribed in the interest of brevity.FIG.8also illustrates an interrupt signal880that can be employed with a serial digital control interface. The interrupt signal880can be utilized when control and calculation of heater resistance is performed within the power converter(s). These then respond to a temperature control signals860(corresponding to temperature set points) provided by the host system.

As illustrated inFIG.9, a system900includes additional switches (“SwB_1,2, . . . n”, another disconnect switch(es)) that can disconnect current sources (“CS_1,2, . . . n”) when, for instance, power is being applied to a plurality of electronic heaters (“Electrical Heater Elements1,2, . . . n”, also “EHE1,2, . . . n”) via the respective conducting disconnect switches (“SwA_1,2, . . . n”) of the respective power converters (“Conv1,2, . . . n”). Additionally, when the disconnect switches (“SwA_1,2, . . . n”) are OFF (open or not conducting) and the respective disconnect switches (“SwB_1,2, . . . n”) are OFF (open or not conducting), the respective electronic heaters (“Electrical Heater Elements1,2, . . . n”) are also OFF. If heater power is AC in nature, or if heater power can be adjusted below the bias of the current source, the circuitry shown inFIG.9can be utilized.

Turning now toFIG.10, illustrated is a system1000including a crosstalk circuit (“CTC1,2, . . . n”) that accommodates “crosstalk” in a plurality of electronic heaters (“Electrical Heater Element1,2, . . . n”, also “EHE1,2, . . . n”). This occurs when the electronic heaters share a common return conductor1070with other independently powered elements, and leakage currents (“Il_1,2, . . . n”) are formed among these elements (i.e., there is return current “crosstalk”). These leakage currents can cause errors in the calculated heater resistance (“RH1,2, . . . n”) because they are not anticipated by the current sources (“CS_1,2, . . . n”). The crosstalk circuit (“CTC1,2, . . . n”) includes a crosstalk circuit current source (“CSCT_1,2, . . . n”) in series with a switch (“SwC_1,2, . . . n”).

To reduce or eliminate these effects, positive and negative polarity current sources (“CSCT_1,2, . . . n”) providing test current (“Ip1,2. . . n”), which may be different that the test current from the respective test current from the current sources (“CS_1,2, . . . n”) are implemented as shown inFIG.10. The current sources (“CSCT_1,2, . . . n”) are switched in 50% of the time positive and the other 50% negative. The resulting output voltages (“V1,2, . . . n_pos, V1,2, . . . n_neg”) on the electronic heaters with a resistance (“RH1,2, . . . n”) and with leakage current (“Il_1,2, . . . n”) and test currents (“Ip1,2, . . . n”) are given as follows.

During the positive current source interval for each electronic heater:

During the negative current source interval for each electronic heater:

The time-averaged signal for each electronic heater is:

Once this term is determined, then the heater resistance can be calculated as via output voltages:

In this manner, the effects of leakage currents induced by other system voltages can be reduced or eliminated.

Thus, a system that can operate with either AC or DC power applied to an electronic heater has been introduced herein. The system utilizes electrical heater resistance to monitor delivered temperature. The system employs independent current source(s) and measuring device(s) such as voltage meter(s) to determine heater resistance during a momentary interruption of heater power flow. This negates effects of power converter self-heating and electronic noise within the power converter. The system can utilize either an analog or serial digital interface to the host system.

The system can also utilize two independent current sources of opposite polarity, and a voltage meter to determine heater resistance during a momentary interruption of heater power flow. The system can compensate for externally induced leakage currents in the electronic heaters. The system can compensate for errors generated through use of common feed or return conductors for the electronic heaters.

In one embodiment, the system (600) (and related method of operating the same) is employable with an electronic heater (620) and includes a power converter (610) coupled to the electronic heater (620) via a disconnect switch (SwA_1) configured to conduct to deliver an output voltage (V1) produced by the power converter (610) to the electronic heater (620) to control a temperature thereof. The system (600) also includes a current source (CS_1) coupled across the electronic heater (620), and a power converter controller (640) configured to adjust the output voltage (V1) produced by the power converter (610) responsive to a test current (Ip1) produced by the current source (CS_1) when the disconnect switch (SwA_1) is not conducting. The electronic heater (620) is configured to be ON when the disconnect switch (SwA_1) is conducting and the electronic heater (620) is configured to operate at a reduced power level when the disconnect switch (SwA_1) is not conducting.

The system (600) also includes a switch controller (SwC1) configured to control conduction of the disconnect switch (SwA_1). The switch controller (SwC1) is configured to control conduction of the disconnect switch (SwA_1) responsive to an interrupt signal (680). The disconnect switch (SwA_1) is configured to conduct when the interrupt signal (680) is disabled and the disconnect switch (SwA_1) is configured not to conduct when the interrupt signal (680) is enabled.

The system (600) also includes a diode (D1) in series with the current source (CS_1) configured to protect the current source (CS_1) from voltages above a controllable output voltage (V1) of the power converter (610). The system (600,900) may also include another disconnect switch (SwB_1) in series with the current source (CS_1) configured to disconnect the current source (CS_1) from the electronic heater (620, EHE1).

In another embodiment, the system (800) (and related method of operating the same) is employable with first and second electronic heaters (EHE1, EHE2) and includes a first power converter (Conv1) coupled to the first electronic heater (EHE1) via a first disconnect switch (SwA_1) configured to conduct to deliver a first output voltage (V1) produced by the first power converter (Conv1) to the first electronic heater (EHE1) to control a temperature thereof. The system (800) also includes a second power converter (Conv2) coupled to the second electronic heater (EHE2) via a second disconnect switch (SwA_2) configured to conduct to deliver a second output voltage (V2) produced by the second power converter (Conv2) to the second electronic heater (EHE2) to control a temperature thereof, The first and second electronic heaters (EHE1, EHE2) share a common return conductor (870) to the first and second power converters (Conv1, Conv2). The system (800) also includes a first current source (CS_1) coupled across the first electronic heater (EHE1), and a second current source (CS_2) coupled across the second electronic heater (EHE2). The system (800) also includes a power converter controller (840) configured to adjust the first and second output voltages (V1, V2) produced by the first and second power converters (Conv1, Conv2), respectively, responsive to first and second test currents (Ip1, Ip2), respectively, produced by the first and second current sources (CS_1, CS_2), respectively, when the first and second disconnect switches (SwA_1, SwA_2), respectively, are not conducting. The first and second electronic heaters (EHE1, EHE2) are configured to be ON when the first and second disconnect switches (SwA_1, SwA_2), respectively, are conducting and the first and second electronic heaters (EHE1, EHE2) are configured to operate at a reduced power level when the first and second disconnect switches (SwA_1, SwA_2), respectively, are not conducting.

The system (800) also includes first and second switch controllers (SwC1, SwC2) configured to control conduction of the first and second disconnect switches (SwA_1, SwA_2), respectively. The first and second switch controllers (SwC1, SwC2) are configured to control conduction of the first and second disconnect switches (SwA_1, SwA_2), respectively, responsive to an interrupt signal (880) from the power converter controller (840). The first and second disconnect switches (SwA_1, SwA_2) are configured to conduct when the interrupt signal (880) is disabled and the first and second disconnect switches (SwA_1, SwA_2) are configured not to conduct when the interrupt signal (880) is enabled.

The system (800) also includes first and second diodes (D1, D2) in series with the first and second current sources (CS_1, CS_2), respectively, configured to protect the first and second current sources (CS_1, CS_2), respectively, from voltages above first and second controllable output voltages (V1, V2,), respectively, of the first and second power converters (Conv1, Conv2), respectively. The system (800,900) also includes another first and second disconnect switches (SwB_1, SwB_2) in series with the first and second current sources (CS_1, CS_2), respectively, configured to disconnect the first and second current sources (CS_1, CS_2), respectively, from the first and second electronic heaters (EHE1, EHE2), respectively The system (800,1000) also includes first and second crosstalk circuits (CTC1, CTC2) coupled across the first and second current sources (CS_1, CS_2), respectively, and to the common return conductor (870,1070) configured to reduce effects of first and second leakage currents (Il_1, Il_2) associated with the first and second electronic heaters (EHE1, EHE2), respectively.

Although the embodiments and its advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the spirit and scope thereof as defined by the appended claims. For example, many of the features and functions discussed above can be implemented in software, hardware, or firmware, or a combination thereof. Also, many of the features, functions, and steps of operating the same can be reordered, omitted, added, etc., and still fall within the broad scope of the various embodiments.