Thermal system with temperature limiting device

Abstract

To provide an apparatus for controlling power to a two-wire heater.SOLUTION: A temperature limiting device for a thermal system includes a modular unit that is configured to connect to a two-wire heater of the thermal system. More specifically, the modular unit includes: a heater interface configured to connect to a two-wire heater of the thermal system; a power interface configured to connect to a power source to receive power; and a controller including a sensor circuit. The sensor circuit is configured to measure an electrical characteristic of the two-wire heater, which includes voltage, current, or a combination thereof. The controller is configured to calculate a temperature of the thermal system based on the measured electrical characteristic and determine whether the temperature is higher than a temperature setpoint.SELECTED DRAWING: Figure 1

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application No. 62 / 831,619, filed April 9, 2019, the disclosure of which is incorporated herein by reference. [Technical Field]

[0002] The present disclosure relates to an apparatus for controlling power to a two-wire heater. [Background technology]

[0003] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

[0004] Resistive heaters are used in a variety of applications to provide heat to a load. Such heaters include, but are not limited to, layered heaters, tubular heaters, cartridge heaters, or other suitable heaters. To determine the appropriate temperature of the heater, a discrete temperature sensor, such as a thermocouple, is placed on or near the heater. Adding a separate temperature sensor to the heater and its environment adds cost and complexity to the overall heating system. Summary of the Invention

[0005] This section provides a general overview of the disclosure and is not an exhaustive disclosure of its entire scope or all of its features.

[0006] The present disclosure provides a temperature limiting device for a thermal system. The temperature limiting device includes a modular unit. The modular unit includes a heater interface configured to connect to a two-wire heater of the thermal system. The modular unit includes a power interface configured to connect to a power source to receive power. The modular unit includes a controller including a sensor circuit. The sensor circuit is configured to measure an electrical characteristic of the two-wire heater, the electrical characteristic including voltage, current, or a combination thereof. The controller is configured to calculate a temperature of the thermal system based on the measured electrical characteristic and determine whether the temperature is greater than a temperature setpoint.

[0007] In some forms, the modular unit further includes a power switch interface for connecting to a power switch of the thermal system, and the controller is configured to operate the power switch to turn off power to the two-wire heater in response to the temperature of the thermal system being greater than a temperature setpoint.

[0008] In some embodiments, the modular unit further comprises a power switch electrically coupled between the power interface and the heater interface and operable by the controller to control power to the two-wire heater.

[0009] In some forms, the controller is configured to turn off power to the two-wire heater via the power switch in response to the temperature of the thermal system being greater than a temperature setpoint.

[0010] In some embodiments, the controller stores predefined heater information associating temperature values ​​of the two-wire heater with measured performance characteristics of the two-wire heater, and the controller is configured to determine the performance characteristics based on the measured electrical characteristics. In some embodiments, the controller is configured to determine a temperature of the two-wire heater, a temperature of a load heated by the two-wire heater, or a combination thereof as a temperature of the thermal system based on the determined performance characteristics and the predefined heater information.

[0011] In some embodiments, the two-wire heater has a varying temperature coefficient of resistance, and the performance characteristic is the resistance of the two-wire heater at a certain temperature.

[0012] In some forms, the heater interface is connected to a two-wire heater via a temperature sensing power pin that defines a temperature sensing junction at the heater, the sensor circuit measures a voltage at the temperature sensing junction, and the performance characteristic is a change in voltage at the temperature sensing junction.

[0013] In some embodiments, the controller is configured to calculate the temperature of the thermal system as the temperature of the two-wire heater, the temperature of a load heated by the two-wire heater, or a combination thereof.

[0014] The present disclosure also provides a thermal system including a two-wire heater including two terminals. The thermal system includes a process controller configured to control thermal performance of the two-wire heater based on data from one or more discrete sensors. The thermal system includes a power switch operable to provide power to the two-wire heater based on a control signal from the process controller. The thermal system includes a temperature limiting device separate from the process controller, the temperature limiting device including a modular unit. The modular unit includes a heater interface configured to connect to the two-wire heater of the thermal system. The modular unit includes a power interface configured to connect to a power source to receive power. The modular unit includes a controller including a sensor circuit. The sensor circuit is configured to measure an electrical characteristic of the two-wire heater, the electrical characteristic including voltage, current, or a combination thereof. The controller is configured to calculate a temperature of the thermal system based on the measured electrical characteristic and determine whether the temperature is greater than a temperature setpoint. The controller is configured to operate the power switch to turn off power to the two-wire heater in response to the temperature of the thermal system being greater than a temperature setpoint.

[0015] In some embodiments, the controller of the temperature limiting device stores predefined heater information correlating temperature values ​​of the two-wire heater with measured performance characteristics of the two-wire heater, and the controller is configured to determine the performance characteristic based on the measured electrical characteristic. In some embodiments, the controller is configured to determine a temperature of the thermal system as a temperature of the two-wire heater, a temperature of a load heated by the two-wire heater, or a combination thereof based on the determined performance characteristic and the predefined heater information.

[0016] In some embodiments, the two-wire heater has a varying temperature coefficient of resistance, and the performance characteristic is the resistance of the two-wire heater at a certain temperature.

[0017] In some embodiments, the two terminals of the two-wire heater include a temperature sensing power pin that defines a temperature sensing junction, the sensor circuitry is configured to measure a voltage at the temperature sensing junction, and the performance characteristic is measured as a change in voltage at the temperature sensing junction.

[0018] In some embodiments, the temperature limiting device is connected in series with the process controller and the power switch, the temperature limiting device being configured to transfer a control signal from the process controller to the power switch.

[0019] In some embodiments, a temperature limiting device is placed in parallel with the power switch to detect an electrical characteristic of the two-wire heater.

[0020] In some embodiments, the modular unit includes a power switch.

[0021] In some embodiments, the two-wire heater is an in-line heater that heats a fluid flowing therethrough. In some embodiments, the power switch is disposed on the in-line heater and is integrated with the in-line heater to transfer heat to the fluid flowing therethrough. In some embodiments, the temperature limiting device is disposed separately from the two-wire heater and the power switch, and the modular unit includes a power switch interface for connecting to the power switch.

[0022] In some embodiments, the thermal system includes a temperature cutoff circuit including a relay coupled to a power line to the two-wire heater. In some embodiments, the thermal system includes a discrete sensor. The two-wire heater is a layered heater having a resistive heating layer. The discrete sensor is configured to measure the temperature of the heater. The temperature cutoff circuit is configured to turn off power to the two-wire heater via the relay if the temperature of the heater is greater than a cutoff temperature setpoint.

[0023] The present disclosure provides a temperature limiting device for a thermal system. The temperature limiting device includes a modular unit. The modular unit includes a heater interface configured to connect to a two-wire heater of the thermal system. The modular unit includes a power interface configured to connect to a power source and receive power. The modular unit includes a power switch disposed between the heater interface and the power interface to control power to the two-wire heater. The modular unit includes a controller including a sensor circuit configured to measure an electrical characteristic of the two-wire heater, the electrical characteristic including voltage, current, or a combination thereof. The controller is configured to calculate a temperature of the thermal system based on the measured electrical characteristic and predefined heater information, determine whether the temperature is greater than a temperature setpoint, and turn off power to the two-wire heater via the power switch in response to the temperature of the thermal system being greater than the temperature setpoint.

[0024] In some embodiments, the controller is configured to calculate the temperature of the thermal system as the temperature of the two-wire heater, the temperature of a load heated by the two-wire heater, or a combination thereof.

[0025] In some forms, the controller is configured to operate in a temperature limit mode that turns off power to the two-wire heater when the temperature of the thermal system is above a temperature setpoint, and in a temperature control mode that selectively applies power to the two-wire heater via the power switch to control the temperature of the thermal system to a temperature control setpoint.

[0026] Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. [Brief explanation of the drawings]

[0027] In order that the present disclosure may be better understood, various forms thereof, given by way of example, will now be described with reference to the accompanying drawings, in which:

[0028] [Figure 1] FIG. 1 illustrates a first embodiment of a thermal system having a temperature limiting device for a two-wire heater in accordance with the teachings of the present disclosure.

[0029] [Figure 2] FIG. 2 illustrates a second configuration of a thermal system having a thermal cutoff device and the temperature limiting device of FIG. 1 in accordance with the teachings of the present disclosure.

[0030] [Figure 3] FIG. 3 illustrates a third configuration of a thermal system having a cascaded process controller and temperature limiting device connected to an external power switch in accordance with the teachings of the present disclosure.

[0031] [Figure 4] FIG. 4 illustrates an in-line heater having a power switch disposed thereon in accordance with the teachings of the present disclosure.

[0032] [Figure 5] FIG. 5 illustrates a fourth configuration of a thermal system having a combined process controller and power switch with a temperature limiter in accordance with the teachings of the present disclosure.

[0033] [Figure 6A] FIG. 6A is a block diagram of a thermal limiting device with a two-wire controller and a power switch.

[0034] [Figure 6B] FIG. 6B is a block diagram of a temperature limiting device with a two-wire controller.

[0035] [Figure 7] FIG. 7 is an example of a cartridge heater with temperature sensitive power pins.

[0036] The drawings described herein are for illustrative purposes and are not intended to limit the scope of the present disclosure in any way. DETAILED DESCRIPTION OF THE INVENTION

[0037] The following description is merely exemplary in nature and is not intended to limit the present disclosure, its application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

[0038] Two-wire thermal systems include two-wire heaters that use two wires (i.e., two power lines) to not only power the heater's resistive heating element to generate heat but also to measure the performance characteristics (e.g., current, voltage, resistance, power, and / or temperature) of the resistive heating element. In one form, a "two-wire" heater includes one or more resistive heating elements defined by a material whose resistance changes with temperature. The material's temperature coefficient of resistance (TCR) must be known and highly stable over a wide temperature range and duty cycle to enable reliable measurements. Such a two-wire system is disclosed in commonly owned U.S. Patent No. 7,196,295, the contents of which are incorporated herein by reference in their entirety. This system is an adaptive thermal system that blends heater design with integrated control of power, resistance, voltage, and current to limit one or more of these parameters (i.e., power, resistance, voltage, and current) while controlling the other parameters in a customizable feedback control system.

[0039] In another aspect, the two-wire heater may include a temperature sensing power pin that provides power to the resistive heating element of the two-wire heater and also measures the temperature via a thermocouple defined by the temperature sensing power pin. Details of the temperature sensing power pin are provided below. Hereinafter, the two-wire heater may be configured as a heater with a varying resistance-temperature relationship, sometimes referred to as an "RT heater," or as a heater with a temperature sensing power pin, sometimes referred to as a "TSPP heater."

[0040] In one aspect, the present disclosure describes a temperature limiting device for controlling power to a two-wire heater based on a performance characteristic of the two-wire heater and / or the temperature of the thermal system. The temperature limiting device of the present disclosure is configured to be an adaptable control device that can be used in existing and new thermal systems having a two-wire heater. The temperature limiting device is configured to: turn off power to the two-wire heater when the temperature of the two-wire heater exceeds a threshold; control the temperature of the heater to a controlled temperature setpoint by selectively turning power on and off to the heater; provide diagnostic control to determine whether one or more performance characteristics of the heater exceed their respective thresholds and take corrective action if the thresholds are exceeded; operate as a safety-related device in conjunction with a secondary safety mechanism; estimate the temperature of the load being heated by the two-wire heater using a known heater-load offset; operate with a process controller for closed-loop control to shut off power to the heater when the temperature of the thermal system exceeds the threshold; and have a power switch operable by the temperature limiting device located with the heater to cool and heat a fluid flowing through the heater. Although specific actions are mentioned, the temperature limiting device may perform other actions as described further herein.

[0041] Referring to FIG. 1 , a thermal system 100 includes a temperature limiting device 102 and a two-wire heater 104 having one or more resistive heating elements 106 for heating a load 108. In one embodiment, the temperature limiting device 102 is connected to a power supply 110 (e.g., 230 VAC) that provides power to the temperature limiting device 102 and the two-wire heater 104. The temperature limiting device 102 includes a two-wire controller (TWC) 112 and a power switch 114 operable by the TWC 112 to interrupt power to the two-wire heater 104. In one embodiment, the power switch 114 may be a thyristor (e.g., a TRIAC). As provided herein, the power switch 114 may be located and integrated as part of the temperature limiting device 102, as shown in FIG. 1 . Alternatively, the power switch 114 may be located external to the temperature limiting device 102.

[0042] In one embodiment, the TWC 112 is configured to monitor the temperature of the thermal system 100 based on electrical characteristics of the resistive heating element 106, such as current and / or voltage. In one embodiment, the temperature of the thermal system 100 may include the temperature of the two-wire heater 104 (i.e., the resistive heating element 106) and / or the temperature of the load 108. In one embodiment, based on the electrical characteristics of the resistive heating element 106 and pre-defined heater information, the TWC 112 is configured to determine performance characteristics of the resistive heating element 106 (i.e., the two-wire heater 104), which are then used to determine the temperature of the thermal system 100. The pre-defined heater information includes information relating a temperature value of the two-wire heater 104 to a performance characteristic measurement of the two-wire heater 104. For example, the performance characteristics for an RT heater may include resistance and / or temperature, and the heater information may include a calculated resistance, a TCR of the material defining the resistive heating element 106, and / or an RT curve / lookup table for determining the temperature of the two-wire heater 104 based on a predefined algorithm. For a TSPP heater, the performance characteristics determined by the TWC 112 may include voltage and / or voltage change, and the heater information may include information relating voltage / voltage change to the temperature of the two-wire heater 104.

[0043] To determine the temperature of the load 108, the heater information may further include a thermal offset. That is, the temperature of the surface of the resistive heating element 106 or the two-wire heater 104 is typically higher than the temperature of the load 108. The difference between these two temperatures is provided as a thermal offset, which may be predefined based on various controlled experiments and used to determine the temperature of the load 108 as the temperature of the thermal system 100. If a thermal offset is provided, the TWC 112 may estimate the temperature of the load 108 by subtracting the thermal offset from the calculated temperature of the two-wire heater 104 (i.e., T L =T H -T O , T L is the heat load temperature, T H is the heater temperature, T O is a thermal offset). Thus, in one embodiment, the TWC 112 may turn off power to the two-wire heater 104 based on the heater temperature and / or the heat load temperature.

[0044] As an example, in the case of an RT heater, the TWC 112 is configured to measure the voltage and / or current applied to the resistive heating element 106 as the electrical characteristic. Based on the measured electrical characteristic and predefined resistance-temperature information of the resistive heating element 106, the TWC 112 determines the resistance value and then the temperature of the resistive heating element 106 as the performance characteristic. As part of the temperature limiting process, the TWC 112 then determines whether the temperature of the resistive heating element 106 exceeds a temperature setpoint (i.e., a temperature limit setpoint). If so, the TWC 112 turns off power to the resistive heating element 106 via the power switch 114. Otherwise, the temperature limiting device 102 continues to supply power to the resistive heating element 106. Alternatively, the TWC 112 may determine the temperature of the load 108 based on a predefined thermal offset and control power to the two-wire heater 104 based on the temperature of the load 108. In this way, the temperature limiting device 102 operates as a safety mechanism to prevent or reduce damage to the two-wire heater 104 in the event of abnormal performance of the two-wire heater 104 (e.g., a temperature higher or lower than a threshold set to prevent damage to the two-wire heater 104). In the following, the TWC 112 operates in a temperature limiting mode by performing the temperature limiting process described herein.

[0045] In one embodiment, the TWC 112 is configured to execute a temperature control process (i.e., operating in a temperature control mode) in which the TWC 112 maintains the temperature of the two-wire heater 104 at a controlled temperature setpoint. In such a configuration, the TWC 112 determines the temperature of the thermal system 100 as described above and turns off power to the resistive heating element 106 when the temperature exceeds the controlled temperature setpoint, while constantly monitoring the temperature of the thermal system 100. For example, in the case of an RT heater, the TWC 112 is configured to calculate the resistance of the resistive heating element 106 in a positive sine wave. Using the resistance value and predefined heater information (e.g., an RT curve / look table, TCR characteristics), the TWC 112 determines the temperature of the resistive heating element 106 and compares it to the controlled temperature setpoint. If the temperature of the resistive heating element 106 exceeds the temperature control setpoint, power to the two-wire heater 104 is turned off at a VAC zero crossing. When the temperature drops below the controlled temperature setpoint, the TWC 112 applies power to the resistive heating element 106 to generate heat.

[0046] In one aspect, the TWC 112 is configured to execute a diagnostic process that controls power to the two-wire heater 104 based on one or more performance characteristics, including temperature, voltage, current, power, and / or resistance. Specifically, if the determined performance characteristic exceeds a respective diagnostic threshold, the TWC 112 determines that the performance of the two-wire heater 104 is abnormal and turns off power to the two-wire heater 104. For example, if the voltage and / or current of the two-wire heater 104 exceeds an associated diagnostic threshold, the temperature limiter 102 turns off power to the two-wire heater 104 as a corrective correction. The diagnostic threshold(s) for each performance characteristic may be a single predefined value or may be set based on the process being executed. For example, a different diagnostic threshold may be set when the two-wire heater 104 is operating in a steady state during warm-up. Thus, the TWC 112 may include a diagnostic mode that performs the operations described above in addition to or instead of the temperature limit mode. Like the temperature limit mode and temperature control mode, the diagnostic mode may be a standard mode available and selectable by the user. Additionally, the various settings / thresholds used in the temperature limit mode, temperature control mode, and diagnostic mode may be the same or different.

[0047] In one embodiment, the TWC 112 is configured to perform a calibration process (i.e., operate in a calibration mode) in which a user communicates with the TWC 112 via a human-machine interface (e.g., a computing device) to calibrate the heater information. Specifically, the heater information provided to the TWC 112 may be updated by uploading new heater information to the TWC 112 or by manually calibrating the heater information provided to the TWC 112. In one example, for manual calibration, a discrete temperature sensor, such as an infrared camera, is used to measure the temperature of the two-wire heater 104, more specifically, the surface temperature of the two-wire heater 104. The TWC 112 calculates the heater temperature as described above and compares the calculated temperature with the temperature measured by the discrete temperature sensor. The TWC 112 may perform this operation against one or more temperature calibration setpoints. Specifically, the TWC 112 provides power to the two-wire heater 104 and calculates the temperature of the two-wire heater 104. Once the temperature equals the selected temperature calibration setpoint, the TWC 112 acquires the temperature measured by the discrete temperature sensor. Based on the temperature difference, the TWC 112 adjusts the heater information, such as updating the RT curve or TCR characteristic used to determine the temperature.

[0048] As described above, TWC 112 may be configured to include one or more operating modes, including a temperature limiting mode, a temperature control mode, a diagnostic mode, and / or a calibration mode. In one variation, TWC 112 may be configured to perform both a temperature limiting process and a temperature control process during operation. In another variation, TWC 112 may be configured to operate in one or more modes, and if multiple modes are available, a user may select the mode to operate via a human-machine interface communicating with temperature limiter 102.

[0049] The temperature limiting device 102 of the present disclosure can improve the response time for shutting off power to the two-wire heater 104 compared to thermal systems with discrete sensors because the temperature limiting device 102 directly measures and limits the temperature of the resistive heating element 106. Conversely, thermal systems with discrete sensors still require sensor data to be processed by the process controller, which can delay power shutoff. Furthermore, the temperature limiting device 102 allows the use of high-watt-density, high-performance heating elements in applications where the entire thermal loop is not known or defined in detail. That is, when a two-wire heater is implemented, the temperature limiting device 102 of the present disclosure can be plugged into an existing thermal system 100 instead of replacing the existing process controller. When the temperature limiting device 102 is used as a safety-related device to suppress severe conditions / failures (e.g., fire), the temperature limiting device 102 may include additional hardware and / or software to meet special requirements, such as secondary safety mechanisms.

[0050] An example of a thermal system including a secondary safety mechanism is provided in FIG. 2. In one embodiment, the thermal system 200 includes a temperature limiting device 102, a heater 202, and a thermal cutoff (TCO) device 204. In one embodiment, the heater 202 is a layered heater having a resistive heating layer defining one or more resistive heating elements 206 and a sensor layer defining a sensor device 208. Such layered heaters are described in commonly assigned U.S. Patent No. 9,078,293, the contents of which are incorporated herein by reference in their entirety. In such layered heaters, the sensor device 208 is provided as a sensor layer made of a material having a TCR ranging from a relatively low value, such as 500 ppm / °C, to a relatively high value, such as 10,000 ppm / °C, and is used to measure the temperature of the load 210. It should be understood that materials having a negative TCR, such as graphite, may also be used. The sensor device 208 may be configured to measure the temperature of the resistive heating element 206 and / or the load 210. Instead of a sensor layer, the sensor device 208 may be a discrete temperature sensor, such as a thermocouple, a resistance temperature detector, or an infrared imager, for measuring the heat load and / or the temperature of the heater 202 .

[0051] The TCO device 204 is coupled to the sensor device 208 and turns off power to the heater 202 when the temperature measured by the sensor device 208 exceeds a defined temperature threshold, which may be the same as or different from the temperature setpoint controlled by the thermal limiting device 102. In one embodiment, the TCO device 204 is an over-temperature detection circuit described in U.S. Patent No. 9,078,293, which includes a voltage divider circuit and a relay for turning off power to the heater 202. In another example, the TCO device 204 may be implemented using a combination of hardware and software to measure the temperature of the load / heater, compare the temperature to a threshold, and activate a relay if the temperature threshold is exceeded. Thus, with the thermal limiting device 102 and TCO device 204 of the present disclosure, the thermal system 200 is configured to include two safety mechanisms.

[0052] The temperature limiting device of the present disclosure is adaptable to various types of thermal systems and, in some embodiments, may utilize an existing power switch provided in the thermal system. Specifically, with reference to Figure 3, a thermal system 300 includes a temperature limiting device 302 including a TWC 304 cascaded with a process temperature controller 306 and a power switch 308. The thermal system further includes a heater 202 and a TCO device 204.

[0053] In one embodiment, the process temperature controller 306 is configured to control the thermal performance of the heater 202 based on data from one or more discrete sensors. Discrete sensors may be located throughout the thermal system 300, such as a temperature sensor 310 located on the heater 202. Thermal performance may include, but is not limited to, controlling the temperature of the resistive heating element 206 and / or the load 210, the thermal profile of the heater 202, and / or the cooling and / or heating rates of the heater 202. In one embodiment, the process temperature controller 306 is a proportional-integral-derivative (PID) controller that uses data from the discrete sensors, including the temperature sensor 310, to determine the temperature of the heater 202 and / or the load 210. Depending on the state of the control loop and the control parameters, the process temperature controller 306 outputs a control signal (e.g., 0-10 V, 0-20 mA, switched DC, open collector, etc.), which is provided to the TWC 304. The TWC 304 transfers a control signal to the power switch 308 and modulates the control signal onto the supply voltage (ie, power from the power supply 110 ) provided through the thermal limiting device 302 .

[0054] The TWC 304 is configured to operate similarly to the TWC 112 to measure the temperature of the thermal system 300. In response to the temperature of the thermal system being greater than a temperature setpoint, the TWC 304 is configured to provide a power control signal to the power switch in place of a control signal from the process controller to turn off power to the heater 202.

[0055] The temperature limiter 302 is compatible with thermal systems that have a power switch. Specifically, the temperature limiter 302 does not interfere with the control loop being executed by the process temperature controller 306. However, if a temperature setpoint is exceeded, the temperature limiter 302 turns off power to the heater 202 and thus the resistive heating element 206, thereby functioning as an upper limit controller.

[0056] 3, the temperature limiter 302 is a separate component and therefore can be used to upgrade an existing process temperature controller 306 that performs closed-loop control. Because the temperature limiter 302 is a separate component, the control signals between the process temperature controller 306 and the TWC 304 should be compatible, and the power switch 308 should be compatible with the voltage-current requirements derived from the resistive heating element 206.

[0057] Similar to temperature limiter 102, temperature limiter 302 directly measures the temperature of resistive heating element(s) 206, thus increasing the response time of temperature limiter 302 compared to systems with discrete sensors. Additionally, temperature limiter 302 is used as a safety-related device to suppress severe conditions / faults (e.g., fire). In addition to the temperature limiting mode, temperature limiter 302 may be configured to include a calibration mode and / or a diagnostic mode, as described above.

[0058] In one variation, instead of the temperature limiter 302 and separate power switch 308, the thermal system 300 may include the temperature limiter 102 described above. In another variation, the thermal system 300 may not include the TCO device 204 and the sensor device 208 to provide a secondary safety mechanism. In yet another variation, the thermal systems 100 and 200 of FIGS. 1 and 2, respectively, may include the temperature limiter 302 and a separate power switch 308. In such a configuration, the TWC 304 sends a power control signal to the power switch 308 to activate or deactivate power to the heater 202. Additionally, the TWC 304 may include the temperature control scheme described above with respect to the TWC 112.

[0059] In one embodiment, the power switch may be integrated with the heater. More specifically, referring to FIG. 4 , as represented by the dotted line, an in-line heater 400 including one or more resistive heating elements (not shown) is configured to heat a fluid flowing through the heater 400. A power switch (PS) 402 is disposed on the in-line heater 400 and is integrated with the in-line heater 400 to transfer heat to the fluid flowing through the in-line heater 400. A sensor device 404 for the TCO device is provided in the in-line heater 400.

[0060] In one embodiment, the power switch 402 is located at the inlet fitting of the in-line heater 400. The fluid flow cools the power switch 402, thus reducing the need for an additional heat sink. That is, the heat loss of the power switch 402 is harnessed not only to cool the power switch 402, but also to preheat the fluid passing through the in-line heater 400.

[0061] In one aspect, when using the heater 400 and power switch 402 as part of the thermal system 300, the process temperature controller 306 measures the temperature of the fluid (liquid or gas) flowing through the in-line heater 400 using a discrete sensor, such as a temperature sensor 310, located along the flow path and / or at the outlet of the heater 400. Depending on the state of the control loop and control parameters, the process temperature controller 306 outputs a control signal (e.g., 0-10 V, 0-20 mA, switched DC, open collector, etc.) that is provided to the TWC 304. The TWC 304 monitors the temperature of the thermal system 300, and if the temperature limit setpoint is not exceeded, the TWC 304 forwards the control signal to the power switch 402, which modulates this signal on the supply voltage.

[0062] In one aspect, the temperature limiting device of the present disclosure is adaptable for use in a thermal system in which a process controller and a power switch are provided as a unit, with the temperature limiting device electrically coupled to the power line to the heater and placed in parallel with the power switch. More specifically, Figure 5 shows a thermal system 500 including a first unit 502 formed by a process controller 504 and a power switch 506, a second unit 507 formed by a two-wire heater 104, a resistive heating element 106, and a discrete sensor 508, and a third unit 510 formed by a temperature limiting device 512. The first unit 502, the second unit 507, and the third unit 510 are generally identified by dotted lines.

[0063] The process controller 504 is configured in a manner similar to the process temperature controller 306 to determine a control signal based on data from a discrete sensor, such as discrete sensor 508. Unlike the process temperature controller 306, the process controller 504 sends a control signal to the power switch 506 via a switch 514 operable by a temperature limiter 512. In one aspect, the switch 514 is a transistor or relay configured to be normally closed and operable by the temperature limiter 512 to decouple the process controller 504 from the power switch 506 and prevent the transmission of the control signal.

[0064] More specifically, the temperature limiting device 512 includes a TWC 516 that is electrically coupled to the power lines supplied to the two-wire heater 104 and that measures an electrical characteristic of the two-wire heater 104. The TWC 516 is configured as a temperature limiting device that turns off power to the two-wire heater 104 based on the temperature of the thermal system 500. For example, if the temperature of the thermal system 500 exceeds a temperature limit setpoint, the TWC 516 operates the switch 514 via a switch signal (e.g., 5V) to prevent the transmission of a control signal to the power switch 506.

[0065] In one variation, instead of the switch 514, the TWC 516 is communicatively coupled to the process controller 504 and notifies the process controller 504 that the temperature of the thermal system 500 has exceeded a temperature limit setpoint and to terminate power to the two-wire heater 104. In another variation, the temperature limiter 512 can be included in the two-wire heater 104. Thus, the switch control signal to the switch 514 and the notification to the process controller 504 are configured to fit existing system components (e.g., the first unit 502). The thermal system 500 does not require an integrated power switch as part of the temperature limiter 512, thus reducing the cost and complexity of the temperature limiter 512.

[0066] 6A and 6B, exemplary block diagrams of a temperature limiting device are shown. FIG. 6A illustrates a temperature limiting device 600 including a modular unit 601 including a TWC 602 and a power switch 604 operable by the TWC 602. The modular unit 601 is a component adaptable to interface with a heater of a thermal system (e.g., two-wire heater 104, 202, or 400). In one aspect, the modular unit 601 includes a heater interface 606, a power interface 608, and an input / output (I / O) interface 610. The heater interface 606 is configured to connect to the two-wire heater, and the power interface 608 is configured to connect to a power source to receive power for the two-wire heater and power for the electronics within the modular unit 601.

[0067] The TWC 602 is configured to communicate with external devices, such as a processor controller (e.g., the process temperature controller 306), one or more human-machine interfaces (HMI(s)), etc., via an I / O interface 610. The HMI(s) enable a user to communicate with the TWC 602 and may include, but are not limited to, a keyboard, a computing device (e.g., a laptop, tablet, smartphone, etc.), a mouse, and / or a display. The HMI(s) enable a user to, for example, select an operating mode of the temperature limiter 600 (e.g., temperature control mode or temperature limiter mode), provide heater information, and / or perform other tasks, such as calibrating heater information. It should be readily understood that the TWC 602 does not need to communicate with the HMI(s) and / or process controller of the thermal system. Furthermore, if communication with external devices is not required, the modular unit 601 need not include the I / O interface 610.

[0068] In one aspect, TWC 602 is configured to include a microprocessor 612, a memory 614 that stores software programs (i.e., computer-readable instructions) executable by microprocessor 612, and a database 616 that stores heater information 618 used to determine the temperature and / or heater performance characteristics of a thermal system, as described above. Memory 614 includes a temperature (temp.) control process 620A for operating TWC 602 in a temperature control mode, a temperature limit process 620B for operating TWC 602 in a temperature limit mode, a calibration process 620C for operating TWC 602 in a calibration mode, and a diagnostic process 620D for operating TWC 602 in a diagnostic mode. It should be readily understood that TWC 602 need not include all of processes 620A-620D, but can be customized to include one or more of the processes described herein.

[0069] The TWC 602 further includes a sensor circuit 620 electrically coupled to the heater via the heater interface 606 to measure electrical characteristics of the heater, more particularly, electrical characteristics of the resistive heating element. In one embodiment, if the heater is a RT heater, the sensor circuit 620 may include a current sensor and / or a voltage sensor to measure the current and voltage applied to the resistive heating element. If the heater is a TSPP-heater, the sensor circuit 620 may include a voltage sensor to measure a change in voltage at a temperature-sensing junction. Thus, the sensor circuit may be configured in a variety of suitable ways based on a two-wire heater.

[0070] Temperature limiter 600 includes an integrated power switch 604 that controls power to the heater based on a signal from TWC 602. In one embodiment, power switch 604 is located between heater interface 606 and power interface 608. Temperature limiter 102 may be configured as temperature limiter 600.

[0071] 6B illustrates a temperature limiter 650 that includes a modular unit 652 that includes a TWC 654, an I / O interface 610, a heater interface 606, and a power interface 608. Here, the temperature limiter 650 controls power to the heater via an external switch (e.g., power switch 308, power switch 402, switch 514). In one embodiment, the TWC 654 is configured to communicate with the external switch via a power switch interface, which may be part of the I / O interface 610 or a separate interface similar to the heater interface 606 and power interface 608. Thus, the TWC 654 can also communicate with a switch for controlling communication between a process controller and the external power switch (e.g., thermal system 500 of FIG. 5) and / or the external power switch (e.g., thermal system 300 of FIG. 3 or the combination of thermal system 300 and power switch 402 of FIG. 4). In this manner, the temperature limiters 302 and 512 may be configured as the temperature limiter 650.

[0072] If the heater includes multiple independently controlled heating elements, the modular units 601, 652 may include multiple heater interfaces 606, power switches 604, and sensor circuits 620 to perform the operations described herein. Furthermore, during a temperature limit mode, the TWCs 602, 654 may be configured to turn off power to all heating elements or only to heating elements that exceed their respective thresholds. While specific components are provided, the modular units 601 and 652 may include other components to provide an adaptive device that can be installed in new and existing thermal systems. For example, the modular unit 601 may include one or more housings, wiring, and / or circuitry. In one aspect, the modular units 601 and 652 may include power circuitry to reduce power from the power source for the electronic components within the modular units.

[0073] As provided above, the heater 104, 202, 400 may have temperature-sensing power pins for supplying power and measuring the heater's temperature. For example, with reference to FIG. 7 , the heater may be a cartridge heater 700 including a resistive heating element 702 having two ends 704, 706. In one embodiment, the resistive heating element 702 is illustratively in the form of a metal wire, such as a nichrome material, wrapped or disposed about a non-conductive portion (or core 708) surrounded by a sheath 709. The core 708 defines a proximal end 710 and a distal end 712, and further defines first and second openings 714 and 716 extending through at least the proximal end 710.

[0074] The cartridge heater 700 further includes a first power pin 718 made from a first conductive material and a second power pin 720 made from a second conductive material that is dissimilar to the first conductive material of the first power pin 718 (i.e., the first and second conductive materials have different Seebeck coefficients). Furthermore, the resistive heating element 702 is made from a material that is different from the first and second conductive materials of the first and second power pins 718, 720, and forms a first junction 722 with the first power pin 718 at an end 704 and a second junction 724 with the second power pin 720 at an other end 706. Because the resistive heating element 702 is made from a different material than the first power pin 718 at the first junction 722 and a different material than the second power pin 720 at the second junction 724 (i.e., the first and second conductive materials have different Seebeck coefficients than the resistive heating element), a thermocouple junction is effectively formed. Thus, the change in voltage at the first and second junctions 722, 724 is detected to determine the average temperature of the cartridge heater 700 without the use of separate / individual temperature sensors.

[0075] Additional details regarding temperature-sensing power pins are described in applicant's co-pending applications, U.S. Serial No. 14 / 725,537, filed May 29, 2015, entitled "RESISTIVE HEATER WITH TEMPERATURE SENSING POWER PINS," and U.S. Serial No. 15 / 950,358, filed April 11, 2018, entitled "RESISTIVE HEATER WITH TEMPERATURE SENSING POWER PINS AND AUXILIARY SENSING JUNCTION." These applications, which are incorporated herein by reference in their entireties, disclose heaters having one or more resistive heating elements connected to power pins that function as thermocouple sensing pins for measuring the temperature of the resistive heating element. Thus, for TSPP heaters, the TWCs 112, 304, 516 of the temperature limiting devices 102, 302, 512 are configured to measure the change in voltage (mV) at the junction formed by the heater's resistive heating element and power pins and calculate the average temperature of the resistive heating element. For example, using a lookup table and / or predefined algorithm, the TWC 112, 304, 516 may perform thermal couple conversion (mV to Temp.) and / or cold junction compensation to determine the temperature of the heating element. If the temperature exceeds a threshold, the TWC 112, 304, 516 can turn off power to the heating element using various methods described herein. The temperature sensing power pin may be used with other heaters, such as fluid line heater(s), fluid immersion heater(s), or other suitable heaters, and should not be limited to cartridge heaters.

[0076] Although the process controller of the present disclosure is described as a PID controller, the controller may be configured as other suitable controllers, such as a model-based controller, an open-loop controller, etc. When configured as a model-based controller, the process controller controls the operation of the heater based on various parameters, such as, but not limited to, power, rate control, thermal profile, boost control using heater-load correlation, and other suitable parameters.

[0077] The description of the present disclosure is merely exemplary in nature and, thus, variations that do not depart from the substance of the disclosure are intended to be within the scope of the present disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the present disclosure.

[0078] Unless otherwise expressly stated, all numerical values ​​expressing mechanical / thermal properties, compositional proportions, dimensions and / or tolerances, or other properties herein are understood to be modified by the word "about" or "approximately" when describing the scope of the present disclosure. This modification is desirable for various reasons, including industry practices, manufacturing techniques, and testing capabilities.

[0079] As used herein, the phrase at least one of A, B, and C should be interpreted to mean the logical (A OR B OR C), using a non-exclusive logical OR, and not to mean "at least one of A, at least one of B, and at least one of C."

[0080] In the diagrams, the direction of the arrows, as indicated by the arrowheads, generally indicates the flow of information (e.g., data or instructions) that is of interest to the diagram. For example, if element A and element B exchange various information, but the information sent from element A to element B is relevant to the diagram, the arrow may point from element A to element B. This unidirectional arrow does not imply that other information is not sent from element B to element A. Furthermore, for information sent from element A to element B, element B may send a request for or acknowledgement of receipt of that information to element A.

[0081] In this application, the term "controller" may be interchanged with the term "circuitry." The controller may be a part of or may include: an application specific integrated circuit (ASIC), digital, analog, or mixed analog / digital discrete circuitry, a digital, analog, or mixed analog / digital integrated circuit, a combinational logic circuit, a field programmable gate array (FPGA), a processor circuit (shared, dedicated, or group) that executes code, a memory circuit (shared, dedicated, or group) that stores code executed by the processor circuit, other suitable hardware components that provide the described functionality, or a combination of some or all of the above, such as a system on a chip.

[0082] The term code includes software, firmware, and / or microcode, and may refer to programs, routines, functions, classes, data structures, and / or objects. The term memory circuit is a subset of the term computer-readable medium. As used herein, the term computer-readable medium does not encompass transitory electrical or electromagnetic signals propagating through a medium (such as on a carrier wave); thus, the term computer-readable medium is considered to be tangible and non-transitory.

Claims

1. 1. A temperature limiting device for a thermal system, comprising: The modular unit is a heater interface configured to connect to a two-wire heater of the thermal system; a power interface configured to connect to a power source to receive power; a controller including a sensor circuit; the sensor circuit is configured to measure an electrical characteristic of the two-wire heater, the electrical characteristic including voltage, current, or a combination thereof; The temperature limiting device, wherein the controller is configured to calculate a temperature of the thermal system based on the measured electrical characteristic and determine whether the temperature is greater than a temperature setpoint.

2. the modular unit further comprising a power switch interface for connecting to a power switch of the thermal system; 10. The temperature limiting device of claim 1, wherein the controller is configured to operate the power switch to turn off power to the heater in response to the temperature of the thermal system being greater than the temperature setpoint.

3. 10. The temperature limiting device of claim 1, wherein the modular unit further comprises a power switch electrically coupled between the power interface and the heater interface, the power switch operable by the controller to control power to the heater.

4. 4. The temperature limiting device of claim 3, wherein the controller is configured to turn off power to the heater via the power switch in response to the temperature of the thermal system being greater than the temperature setpoint.

5. the controller stores predefined heater information associating temperature values ​​of the two-wire heater with measurements of performance characteristics of the two-wire heater, and the controller is configured to determine the performance characteristics based on the measured electrical characteristics; 2. The temperature limiting device of claim 1, wherein the controller is configured to determine, based on the determined performance characteristics and the predefined heater information, the temperature of the thermal system as the temperature of the two-wire heater, the temperature of a load heated by the two-wire heater, or a combination thereof.

6. 6. The temperature limiting device of claim 5, wherein the two-wire heater has a varying temperature coefficient of resistance, and the performance characteristic is the resistance of the heater at a given temperature.

7. 6. The thermal limiting device of claim 5, wherein the heater interface is connected to the two-wire heater via a temperature sensing power pin that defines a temperature sensing junction at the heater, the sensor circuit measures a voltage at the temperature sensing junction, and the performance characteristic is a change in voltage at the temperature sensing junction.

8. The temperature limiting device of claim 1 , wherein the controller is configured to calculate the temperature of the thermal system as the temperature of the two-wire heater, the temperature of a load heated by the two-wire heater, or a combination thereof.

9. 1. A thermal system comprising: a two-wire heater including two terminals; a process controller configured to control thermal performance of the two-wire heater based on data from one or more discrete sensors; a power switch operable to supply power to the two-wire heater based on a control signal from the process controller; a temperature limiting device separate from the process; The modular unit is a heater interface configured to connect to a two-wire heater of the thermal system; a power interface configured to connect to a power source to receive power; a controller including a sensor circuit; the sensor circuit is configured to measure an electrical characteristic of the two-wire heater, the electrical characteristic including voltage, current, or a combination thereof; the controller is configured to calculate a temperature of the thermal system based on the measured electrical characteristic and determine whether the temperature is greater than a temperature setpoint; the controller is configured to operate the power switch to turn off power to the heater in response to the temperature of the thermal system being greater than the temperature setpoint. A thermal system comprising the temperature limiting device.

10. the controller of the temperature limiting device stores predefined heater information associating temperature values ​​of the two-wire heater with measurements of performance characteristics of the two-wire heater, and the controller is configured to determine the performance characteristics based on the measured electrical characteristics; 10. The thermal system of claim 9, wherein the controller is configured to determine, as the temperature of the thermal system, a temperature of the two-wire heater, a temperature of a load heated by the two-wire heater, or a combination thereof, based on the determined performance characteristics and the predefined heater information.

11. 11. The thermal system of claim 10, wherein the two-wire heater has a varying temperature coefficient of resistance, and the performance characteristic is the resistance of the two-wire heater at a temperature.

12. two terminals of the two-wire heater including a temperature sensing power pin defining a temperature sensing junction; The thermal system of claim 10 , wherein the sensor circuit is configured to measure a voltage at the temperature sensitive junction, and the performance characteristic is a change in voltage at the temperature sensitive junction.

13. The thermal system of claim 9 , wherein the temperature limiting device is disposed in parallel with the power switch and detects an electrical characteristic of the heater.

14. The thermal system of claim 9 , wherein the modular unit includes the power switch.

15. the two-wire heater is an in-line heater that heats a fluid flowing therethrough; the power switch is disposed on the in-line heater and is integrated with the in-line heater to transfer heat to the fluid flowing through the in-line heater; The thermal system of claim 9 , wherein the temperature limiting device is located separately from the two-wire heater and the power switch, and the modular unit includes a power switch interface for connecting to the power switch.

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