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 on April 9, 2019. The disclosure of the above application is incorporated herein by reference.

Technical Field

[0002] This disclosure relates to an apparatus for controlling the power of a two - wire heater.

Background Art

[0003] The description in this section merely provides background information related to the present disclosure and does not constitute prior art.

[0004] Resistive heaters are used in various applications to provide heat to a load. Such heaters include, but are not limited to, sheet heaters, tubular heaters, cartridge heaters, or other suitable heaters. To determine the appropriate temperature of the heater, discrete temperature sensors such as thermocouples are installed on or near the heater. Adding individual temperature sensors to the heater and its environment is costly and makes the entire heating system complex. [[ID=​​​​​​​​​This disclosure provides a temperature limiting device for a thermal system. The temperature limiting device comprises 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 which includes a sensor circuit. The sensor circuit is configured to measure the electrical characteristics of the two-wire heater, which include voltage, current, or a combination thereof. The controller is configured to calculate the temperature of the thermal system based on the measured electrical characteristics and to determine whether the temperature is higher than a temperature setpoint.

[0007] In some configurations, 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 configurations, the modular unit further includes a power switch, operable by a controller, which is electrically coupled between the power interface and the heater interface to control power to a two-wire heater.

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

[0010] In some configurations, the controller stores predefined heater information relating the temperature value of the two-wire heater to 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 configurations, the controller is configured to determine the temperature of the thermal system as the temperature of the two-wire heater, the temperature of the load heated by the two-wire heater, or a combination thereof, based on the determined performance characteristics and the predefined heater information.

[0011] In some forms, a two-wire heater exhibits a change in the temperature coefficient of its resistance, and its performance characteristic is the resistance value of the two-wire heater at a given temperature.

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

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

[0014] This disclosure also provides a thermal system including a two-wire heater having two terminals. The thermal system includes a process controller configured to control the thermal performance of the two-wire heater based on data from one or more discrete sensors. The thermal system includes a power switch that can be operated to supply power to the two-wire heater based on a control signal from the process controller. The thermal system includes a temperature limiter separate from the process controller, the temperature limiter includes 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 the electrical characteristics of the two-wire heater, which include voltage, current, or a combination thereof. The controller is configured to calculate the temperature of the thermal system based on the measured electrical characteristics and to determine whether the temperature is above 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 above the temperature setpoint.

[0015] In some configurations, the temperature limiting device controller stores predefined heater information relating the temperature value of a two-wire heater to 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 configurations, the controller is configured to determine the temperature of the thermal system as the temperature of the two-wire heater, the temperature of the load heated by the two-wire heater, or a combination thereof, based on the determined performance characteristics and the predefined heater information.

[0016] In some forms, a two-wire heater exhibits a change in the temperature coefficient of its resistance, and its performance characteristic is the resistance value of the two-wire heater at a given temperature.

[0017] In some configurations, the two terminals of a two-wire heater include temperature-sensing power pins that define a temperature-sensing junction, and the sensor circuit is configured to measure the voltage at the temperature-sensing junction, with the performance characteristics measured as the change in voltage at the temperature-sensing junction.

[0018] In some configurations, the temperature limiter is connected in series with the process controller and the power switch, and the temperature limiter is configured to transfer control signals from the process controller to the power switch.

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

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

[0021] In some configurations, the two-wire heater is an inline heater that heats the fluid flowing through it. In some configurations, the power switch is located on the inline heater and is integrated with the inline heater to transfer heat to the fluid flowing within the inline heater. In some configurations, the temperature limiter is located separately from the two-wire heater and the power switch, and the modular unit includes a power switch interface for connection to the power switch.

[0022] In some embodiments, the thermal system includes a temperature cutoff circuit, which includes a relay coupled to the power lines to a two-wire heater. In some embodiments, the thermal system includes a discrete sensor. The two-wire heater is a layered heater having a resistance 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 heater temperature is above 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 to 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 that includes a sensor circuit, the sensor circuit being configured to measure electrical characteristics of the two-wire heater, the electrical characteristics including voltage, current, or a combination thereof. The controller is configured to calculate the temperature of the thermal system based on the measured electrical characteristics and predefined heater information, determine whether the temperature is higher than a temperature setpoint, and in response to the temperature of the thermal system being higher than the temperature setpoint, turn off power to the two-wire heater via the power switch.

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

[0025] In some forms, the controller operates in a temperature limiting mode to turn off power to the two-wire heater when the temperature of the thermal system is higher than the temperature setpoint, and is configured to operate in a temperature control mode to selectively apply power to the two-wire heater via the power switch to control the temperature of the thermal system to a temperature control setpoint.

[0026] Additional applicable areas will become apparent from the description provided herein. It should be understood that the description and specific examples are for illustrative purposes only and are not intended to limit the scope of the present disclosure.

Brief Description of the Drawings

[0027] As the present disclosure is better understood, its various forms given by way of example will be described with reference to the accompanying drawings.

[0028] [Figure 1] Figure 1 shows a first form 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] Figure 2 shows a second form of a thermal system having a thermal cutoff device and the temperature limiting device of Figure 1 in accordance with the teachings of the present disclosure.

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

[0031] [Figure 4] Figure 4 shows an in-line heater having a power switch provided in the in-line heater in accordance with the teachings of the present disclosure.

[0032] [Figure 5] Figure 5 shows a fourth form of a thermal system having a power switch with a combined process controller and a temperature limiting device in accordance with the teachings of the present disclosure.

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

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

[0035] 〈0000134〉Figure 7 is an example of a cartridge heater having a temperature sensing power pin.

[0036] The drawings included herein are for illustrative purposes only and are not intended to limit the scope of this disclosure in any way. [Modes for carrying out the invention]

[0037] The following descriptions are purely illustrative and are not intended to limit this disclosure, application, or use. Throughout the drawings, corresponding reference figures should be understood to indicate similar or corresponding parts and features.

[0038] A two-wire thermal system includes a two-wire heater that uses two wires (i.e., two power lines) not only to power the resistive heating element of the heater to generate heat, but also to measure the performance characteristics of the resistive heating element (e.g., current, voltage, resistance, power, and / or temperature). In one embodiment, a “two-wire” heater includes one or more resistive heating elements defined by a material whose resistance varies with temperature. The temperature coefficient (TCR) of the resistance of the material is known and needs to be large and stable over a wide temperature range and load cycle to enable reliable measurements. Such a two-wire system is disclosed in U.S. Patent No. 7,196,295, which is owned jointly with this application and is incorporated herein by reference in its entirety. This system is an adaptive thermal system that combines heater design with control incorporating power, resistance, voltage, and current, controlling other parameters while limiting one or more of these parameters (i.e., power, resistance, voltage, and current) in a customizable feedback control system.

[0039] In another embodiment, a two-wire heater may include a temperature-sensing power pin that supplies power to the resistive heating element of the two-wire heater and measures temperature via a thermocouple defined by a temperature-sensing power pin. Details of the temperature-sensing power pin are as follows. Hereinafter, the two-wire heater may be configured as a heater having a changing resistance-temperature correlation, sometimes referred to as an "RT heater," or as a heater having a temperature-sensing power pin, sometimes referred to as a "TSPP heater."

[0040] In one embodiment, the disclosure describes a temperature limiting device for controlling power to a two-wire heater based on the performance characteristics of the two-wire heater and / or the temperature of the thermal system. The temperature limiting device of the 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 heater temperature to a controlled temperature setpoint by selectively turning power to the heater on or off; perform diagnostic control to determine whether one or more performance characteristics of the heater exceed their respective thresholds and take corrective action if they do; operate as a safety-related device in conjunction with a secondary safety mechanism; estimate the temperature of the load heated by the two-wire heater using a known heater-load offset; operate with a closed-loop control process controller to cut off power to the heater when the temperature of the thermal system exceeds a threshold; and have a power switch that can be operated by the temperature limiting device located with the heater, cool the power switch, and heat the fluid flowing through the heater. While specific operations are listed, the temperature limiting device may perform other operations as further described herein.

[0041] Referring to Figure 1, the thermal system 100 includes a temperature limiter 102 and a two-wire heater 104 having one or more resistance heating elements 106 for heating a load 108. In one embodiment, the temperature limiter 102 is connected to a power supply 110 (e.g., 230VAC) that supplies power to the temperature limiter 102 and the two-wire heater 104. The temperature limiter 102 includes a two-wire controller (TWC) 112 and a power switch 114 that can be operated by the TWC 112 to cut off power to the two-wire heater 104. In one embodiment, the power switch 114 may be a thyristor (e.g., TRIAC). As provided herein, the power switch 114 may be located as part of and integrated with the temperature limiter 102, as shown in Figure 1. Alternatively, the power switch 114 may be located outside the temperature limiter 102.

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

[0043] To determine the temperature of load 108, the heater information may further include a thermal offset. That is, the surface temperature of the resistance heating element 106 or the two-wire heater 104 is typically higher than the temperature of load 108. The difference between these two temperatures is provided as a thermal offset, which is predefined based on various controlled experiments and can be used to determine the temperature of load 108 as the temperature of the thermal system 100. If a thermal offset is provided, the TWC 112 may estimate the temperature of 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 The thermal load temperature is T H is heater temperature, T O (This is a thermal offset.) Therefore, in one embodiment, the TWC112 may turn off the power to the two-wire heater 104 based on the heater temperature and / or the thermal load temperature.

[0044] For example, in the case of an RT heater, the TWC112 is configured to measure the voltage and / or current applied to the resistive heating element 106 as an electrical characteristic. Based on the measured electrical characteristics and predefined resistance-temperature information of the resistive heating element 106, the TWC112 determines the resistance value of the resistive heating element 106 as a performance characteristic, and then determines its temperature. As part of the temperature limiting process, the TWC112 then determines whether the temperature of the resistive heating element 106 exceeds the temperature setpoint (i.e., the temperature limit settingpoint). If so, the TWC112 turns off the 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 TWC112 may determine the temperature of the load 108 based on a predefined thermal offset and control the power to the two-wire heater 104 based on the temperature of the load 108. As a result, the temperature limiting device 102 acts as a safety mechanism to suppress or reduce damage to the two-wire heater 104 if abnormal performance occurs in the two-wire heater 104 (for example, a temperature higher or lower than the threshold set to suppress damage to the two-wire heater 104). Hereafter, the TWC 112 operates in temperature limiting mode by performing the temperature limiting process described herein.

[0045] In one embodiment, the TWC112 is configured to perform a temperature control process (i.e., operation in temperature control mode) that maintains the temperature of the two-wire heater 104 at a controlled temperature setpoint. In such a configuration, the TWC112 determines the temperature of the thermal system 100 as described above and turns off the power to the resistive heating element 106 when the temperature exceeds the controlled temperature setpoint, while continuously monitoring the temperature of the thermal system 100. For example, in the case of an RT heater, the TWC112 is configured to calculate the resistance value of the resistive heating element 106 in a positive sine wave. Using the resistance value and predefined heater information (e.g., RT curve / looktable, TCR characteristics), the TWC112 determines the temperature of the resistive heating element 106 and compares it with the controlled temperature setpoint. When the temperature of the resistive heating element 106 exceeds the temperature control setpoint, the power to the two-wire heater 104 is turned off at the VAC zero-crossing. When the temperature falls below a controlled temperature setpoint, the TWC112 applies power to the resistance heating element 106 to generate heat.

[0046] In one embodiment, the TWC112 is configured to perform a diagnostic process that controls the 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 characteristics exceed their respective diagnostic thresholds, the TWC112 determines that the performance of the two-wire heater 104 is abnormal and turns off the power to the two-wire heater 104. For example, if the voltage and / or current of the two-wire heater 104 exceed the relevant diagnostic thresholds, the temperature limiter 102 turns off the power to the two-wire heater 104 as a corrective measure. The diagnostic threshold(s) for each performance characteristic may be a single predefined value or may be set based on the process being performed. For example, different diagnostic thresholds may be set when the two-wire heater 104 is operating in steady-state bursts during warm-up. Thus, the TWC112 may include a diagnostic mode that performs the above-described operation in addition to, or instead of, the temperature limiting mode. Similar to the temperature limit mode and temperature control mode, the diagnostic mode may be a standard mode available and selectable by the user. Furthermore, 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 TWC112 is configured to perform a calibration process (i.e., operation in calibration mode) in which a user communicates with the TWC112 via a human-machine interface (e.g., a computing device) to calibrate heater information. Specifically, the heater information provided to the TWC112 may be updated by uploading new heater information to the TWC112 or by manually calibrating the heater information provided to the TWC112. 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 TWC112 calculates the heater temperature as described above and compares the calculated temperature with the temperature measured by the discrete temperature sensor. The TWC112 may perform such operations for one or more temperature calibration setpoints. Specifically, the TWC112 supplies power to the two-wire heater 104 and calculates the temperature of the two-wire heater 104. When the temperature equals the selected temperature calibration setpoint, the TWC112 acquires the temperature measured by the discrete temperature sensor. Based on the temperature difference, the TWC112 adjusts the heater information, such as updating the RT curve or TCR characteristics used to determine the temperature.

[0048] As described above, the TWC112 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 modification, the TWC112 may be configured to perform both a temperature limiting process and a temperature control process during operation. In another modification, the TWC112 may be configured to operate one or more modes, and if multiple modes are available, the user may select the mode to perform via a human-machine interface that communicates with the temperature limiting device 102.

[0049] The temperature limiting device 102 of this disclosure can improve the response time for cutting off power to the two-wire heater 104 compared to a thermal system with discrete sensors, because the temperature limiting device 102 directly measures and limits the temperature of the resistance heating element 106. Conversely, in a thermal system with discrete sensors, the sensor data still needs to be processed by the process controller, which can delay power cutoff. Furthermore, the temperature limiting device 102 can use high-watt-density, high-performance heating elements even in applications where the entire thermal loop is unknown or not defined in detail. That is, when a two-wire heater is implemented, the temperature limiting device 102 of this 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 Figure 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 resistance heating layer defining one or more resistance heating elements 206 and a sensor layer defining a sensor device 208. Such a layered heater is described in U.S. Patent No. 9,078,293, which is assigned in common with this application and whose contents are incorporated herein by reference in whole. In the case of such a layered heater, 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 also be understood that a material having a negative TCR, such as graphite, may be used. The sensor device 208 may be configured to measure the temperature of the resistance heating elements 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, resistance temperature detector, or infrared image sensor for measuring the temperature of the heat load and / or heater 202.

[0051] The TCO device 204 is coupled to the sensor device 208 and, when the temperature measured by the sensor device 208 exceeds a defined temperature threshold, turns off the power to the heater 202, which may be the same as or different from the temperature setpoint controlled by the temperature limiting device 102. In one embodiment, the TCO device 204 is an overtemperature detection circuit described in U.S. Patent No. 9,078,293, and includes a divider circuit and a relay for turning off the 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 the relay if the temperature threshold is exceeded. Thus, the temperature limiting device 102 and the TCO device 204 of this disclosure configure the thermal system 200 to include two safety mechanisms.

[0052] The temperature limiting devices of this disclosure are adaptable to various types of thermal systems, and in some forms, existing power switches provided in the thermal system may be utilized. Specifically, referring to Figure 3, the thermal system 300 includes a temperature limiting device 302 which includes 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. The discrete sensors may be provided throughout the thermal system 300, such as a temperature sensor 310 provided 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 rate and / or heating rate of the heater 202. In one embodiment, the process temperature controller 306 is a proportional-integral-derivative (PID) controller that uses data from discrete sensors, including a 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., 0-10V, 0-20mA, switched DC, open collector, etc.), which is supplied to the TWC 304. TWC304 transfers the control signal to the power switch 308, which modulates the control signal over the supply voltage (i.e., power from power supply 110) supplied via the temperature limiter 302.

[0054] The TWC304 operates similarly to the TWC112 and is configured to measure the temperature of the thermal system 300. The TWC304 is configured to provide a power control signal to the power switch, instead of a control signal from the process controller, in order to turn off power to the heater 202 in response to the temperature of the thermal system being higher than the temperature setpoint.

[0055] The temperature limiting device 302 is adaptable to thermal systems with power switches. Specifically, the temperature limiting device 302 does not interfere with the control loop performed by the process temperature controller 306. However, if the temperature exceeds the setpoint, the temperature limiting device 302 turns off the power to the heater 202 and, consequently, the resistive heating element 206, thereby functioning as a high-limit controller.

[0056] In the thermal system 300 of Figure 3, the temperature limiter 302 is a separate component and can therefore 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 the temperature limiting device 102, the temperature limiting device 302 directly measures the temperature of one or more resistance heating elements 206, and therefore increases the response time of the temperature limiting device 302 compared to a system with discrete sensors. Furthermore, the temperature limiting device 302 is used as a safety-related device to suppress severe conditions / failures (e.g., fire). In addition to the temperature limiting mode, the temperature limiting device 302 may be configured to include a calibration mode and / or a diagnostic mode, as described above.

[0058] In one modification, instead of the temperature limiting device 302 and a separate power switch 308, the thermal system 300 may include the temperature limiting device 102 described above. In another modification, the thermal system 300 may not include the TCO device 204 and the sensor device 208 for providing a secondary safety mechanism. In yet another modification, the thermal systems 100 and 200 in Figures 1 and 2 may each include the temperature limiting device 302 and a separate power switch 308. In such a configuration, the TWC 304 transmits a power control signal to the power switch 308 to activate or deactivate power to the heater 202. Furthermore, 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 Figure 4, as shown by the dotted line, an inline heater 400 including one or more resistance heating elements (not shown) is configured to heat the fluid flowing through the heater 400. A power switch (PS) 402 is located on the inline heater 400 and is integrated with the inline heater 400 to transfer heat to the fluid flowing through the inline heater 400. A sensor device 404 for the TCO device is provided on the inline heater 400.

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

[0061] In one embodiment, when using a heater 400 and a power switch 402 as part of a thermal system 300, the process temperature controller 306 measures the temperature of the fluid (liquid or gas) flowing through the inline heater 400 using discrete sensors such as a temperature sensor 310 located along and / or at the outlet of the heater 400. Depending on the state of the control loop and the control parameters, the process temperature controller 306 outputs a control signal (e.g., 0-10V, 0-20mA, 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 it does not exceed the temperature limit setpoint, the TWC 304 transfers the control signal to the power switch 402, which modulates this signal over the supply voltage.

[0062] In one embodiment, the temperature limiting device of the present disclosure is provided as a unit comprising a process controller and a power switch, and the temperature limiting device is electrically coupled to the power lines to the heater and is adaptable for use in a thermal system arranged in parallel with the power switch. More specifically, Figure 5 shows a thermal system 500 comprising 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 resistance 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 similar manner to the process temperature controller 306 to determine a control signal based on data from discrete sensors such as discrete sensor 508. Unlike the process temperature controller 306, the process controller 504 transmits the control signal to the power switch 506 via a switch 514 that is operable by the temperature limiting device 512. In one embodiment, the switch 514 is a transistor or relay configured to be normally closed, and is operable by the temperature limiting device 512 to disconnect the process controller 504 from the power switch 506, thereby preventing 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 line supplying the two-wire heater 104 and measures the electrical characteristics 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 activates a switch 514 via a switch signal (e.g., 5V) and prevents the transmission of a control signal to the power switch 506.

[0065] In one modification, instead of switch 514, TWC 516 is communicatively coupled to process controller 504 to notify process controller 504 that the temperature of thermal system 500 exceeds a temperature limit setpoint and to cut off power to the two-wire heater 104. In another modification, the temperature limiting device 512 can be provided on the two-wire heater 104. Thus, the switch control signals to switch 514 and the notifications to process controller 504 are configured to fit existing system components (e.g., first unit 502). Thermal system 500 does not require a power switch integrated as part of the temperature limiting device 512, thus reducing the cost and complexity of the temperature limiting device 512.

[0066] Referring to Figures 6A and 6B, exemplary block diagrams of a temperature limiting device are shown. Figure 6A shows a temperature limiting device 600 including a modular unit 601 which includes 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 in the thermal system (e.g., two-wire heaters 104, 202, or 400). In one embodiment, 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 a two-wire heater, and the power interface 608 is configured to connect to a power supply to receive power for the two-wire heater and for the electronics within the modular unit 601.

[0067] The TWC602 is configured to communicate with external devices such as a processor controller (e.g., a process temperature controller 306) and one or more human-machine interfaces (HMI(s)) via the I / O interface 610. The HMI(s) enable a user to communicate with the TWC602 and may include, but are not limited to, a keyboard, computing device (e.g., a laptop, tablet, smartphone, etc.), mouse, and / or display. The HMI(s) allows the user to perform other tasks, such as selecting the operating mode of the temperature limiter 600 (e.g., temperature control mode or temperature limiter mode), providing heater information, and / or calibrating the heater information. It should be readily understood that the TWC602 does not need to communicate with the thermal system's HMI(s) and / or process controller. Furthermore, if communication with external devices is not required, the modular unit 601 may not include the I / O interface 610.

[0068] In one embodiment, the TWC602 is configured to include a microprocessor 612, a memory 614 for storing software programs (i.e., computer-readable instructions) executable by the microprocessor 612, and a database 616 for storing heater information 618 used to determine the temperature and / or performance characteristics of the heaters of the thermal system, as described above. The memory 614 includes a temperature (temp.) control process 620A for operating the TWC602 in temperature control mode, a temperature limiting process 620B for operating the TWC602 in temperature limiting mode, a calibration process 620C for operating the TWC602 in calibration mode, and a diagnostic process 620D for operating the TWC602 in diagnostic mode. It should be readily understood that the TWC602 does not need to include all of processes 620A to 620D and can be customized to include one or more of the processes described herein.

[0069] The TWC602 further includes a sensor circuit 620 electrically coupled to the heater via a heater interface 606, which measures the electrical characteristics of the heater, more specifically the electrical characteristics of the resistive heating element. In one embodiment, if the heater is an RT heater, the sensor circuit 620 may include a current sensor and / or a voltage sensor for measuring 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 for measuring the voltage change at the temperature sensing junction. Thus, the sensor circuit may be configured in various suitable ways based on a two-wire heater.

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

[0071] Figure 6B shows a temperature limiting device 650 including a modular unit 652 which includes a TWC654, an I / O interface 610, a heater interface 606, and a power interface 608. Here, the temperature limiting device 650 controls power to the heater via external switches (e.g., power switch 308, power switch 402, switch 514). In one embodiment, the TWC654 is configured to communicate with external switches via a power switch interface which can be part of the I / O interface 610 or a separate interface similar to the heater interface 606 and power interface 608. Thus, the TWC654 can also communicate with switches for controlling communication between the process controller and an external power switch (e.g., the thermal system 500 in Figure 5) and / or an external power switch (e.g., the thermal system 300 in Figure 3 or a combination of the thermal system 300 and power switch 402 in Figure 4). In this way, temperature limiting devices 302 and 512 may be configured as the temperature limiting device 650.

[0072] If the heater includes multiple independently controlled heating elements, the modular units 601 and 652 may include multiple heater interfaces 606, power switches 604, and sensor circuits 620 for performing the operations described herein. Furthermore, during temperature limiting modes, the TWCs 602 and 654 may be configured to turn off power to all heating elements or to turn off power 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 adaptive devices 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 circuits, etc. In one embodiment, the modular units 601 and 652 may include power circuits for reducing power from the power supply for electronic components within the modular unit.

[0073] As provided above, heaters 104, 202, and 400 may have temperature-sensing power pins for supplying power and measuring the heater temperature. Referring to Figure 7, for example, 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 exemplary in the form of a metal wire such as nichrome material and is wound around or arranged around 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 at least through the proximal end 710.

[0074] The cartridge heater 700 further comprises a first power pin 718 made of a first conductive material and a second power pin 720 made of a second conductive material different from 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 of a material different from the first and second conductive materials of the first and second power pins 718 and 720, forming a first joint 722 with the first power pin 718 at end 704 and a second joint 724 with the second power pin 720 at other end 706. Since the resistive heating element 702 is made of a different material from the first power pin 718 at the first joint 722 and a different material from the second power pin 720 at the second joint 724 (i.e., the first and second conductive materials have different Seebeck coefficients), a thermocouple joint is effectively formed. Therefore, voltage changes at the first and second junctions 722 and 724 are detected, and the average temperature of the cartridge heater 700 is determined without the use of separate temperature sensors.

[0075] Further details relating to temperature-sensing power pins are described in the applicant's jointly pending applications filed on 29 May 2015, titled “RESISTIVE HEATER WITH TEMPERATURE SENSING POWER PINS” with U.S. serial number 14 / 725,537, and filed on 11 April 2018, titled “RESISTIVE HEATER WITH TEMPERATURE SENSING POWER PINS AND AUXILIARY SENSING JUNCTION” with U.S. serial number 15 / 950,358. These applications, which are incorporated herein by reference in their entirety, disclose a heater having one or more resistive heat elements connected to power pins that function as thermocouple sensing pins for measuring the temperature of the resistive heat elements. Thus, in the case of a TSPP heater, 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 resistive heat elements and power pins of the heater and to calculate the average temperature of the resistive heat elements. For example, using a lookup table and / or a predefined algorithm, the TWC112, 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 TWC112, 304, 516 may turn off power to the heating element using one of the methods described herein. The temperature-sensing power pin may be used with other heaters, such as fluid line heaters, fluid immersion heaters, or other suitable heaters, and should not be limited to cartridge heaters.

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

[0077] The descriptions in this disclosure are essentially illustrative, and any modifications that do not deviate from the substance of this disclosure are intended to be within the scope of this disclosure. Such modifications shall not be deemed to deviate from the spirit and scope of this disclosure.

[0078] In this specification, unless otherwise explicitly stated, all numerical values ​​indicating mechanical / thermal properties, composition ratios, dimensions and / or tolerances, or other properties are to be understood as modified with the word "approximately" or "about" when describing the scope of this disclosure. This modification is desirable for a variety of reasons, including industrial practice, manufacturing techniques, and test capabilities.

[0079] As used herein, the phrase "at least one of A, B, and C" should be interpreted to mean 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 diagrams, the direction of the arrows, as indicated by the arrowheads, generally indicates the flow of information (such as data or commands) that is of interest to the diagram. For example, if element A and element B exchange various pieces of information, and 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 one-way arrow does not mean that no other information is sent from element B to element A. Furthermore, with respect to the information sent from element A to element B, element B may send a request for or acknowledgment of receipt of that information to element A.

[0081] In this application, the term "controller" may be replaced with the term "circuit." The controller may be a part of or may include: an ASIC (Application Specific Integrated Circuit), a digital, analog, or mixed analog / digital discrete circuit, a digital, analog, or mixed analog / digital integrated circuit, a combinational logic circuit, an FPGA (Field Programmable Gate Array), a processor circuit (shared, dedicated, or grouped) that executes code, a memory circuit (shared, dedicated, or grouped) that stores code executed by the processor circuit, other suitable hardware components that provide the described functions, 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 include transient electrical or electromagnetic signals propagating through a medium (such as on a carrier wave), and therefore the term "computer-readable medium" is considered to refer to something tangible and non-transient. The invention described in the original claims of this application is listed below. [1] A temperature limiting device for a thermal system, The modular unit is A heater interface configured to connect to a two-wire heater of the aforementioned thermal system, A power interface configured to connect to a power source in order to receive power, A controller including a sensor circuit, The sensor circuit is configured to measure the electrical characteristics of the two-wire heater, and the electrical characteristics include voltage, current, or a combination thereof. The controller is a temperature limiting device configured to calculate the temperature of the thermal system based on the measured electrical characteristics and to determine whether the temperature is higher than a temperature setpoint. [2] The modular unit further comprises a power switch interface for connecting to the power switch of the thermal system, The temperature limiting device according to [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 higher than the temperature setpoint. [3] The temperature limiting device according to [1], further comprising a power switch electrically coupled between the power interface and the heater interface and operable by the controller for controlling power to the heater. [4] The temperature limiting device according to [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 higher than the temperature setpoint. [5] The controller stores predefined heater information relating the temperature value of the two-wire heater to measured values ​​of the performance characteristics of the two-wire heater, and the controller is configured to determine the performance characteristics based on the measured electrical characteristics. The temperature limiting device according to [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 the load heated by the two-wire heater, or a combination thereof. [6] The temperature limiting device described in [5], wherein the two-wire heater has a temperature coefficient of resistance that changes, and the performance characteristic is the resistance value of the heater at a certain temperature. [7] The heater interface is connected to the two-wire heater via a temperature-sensing power pin that defines a temperature-sensing junction in the heater, the sensor circuit measures the voltage at the temperature-sensing junction, and the performance characteristic is the change in voltage at the temperature-sensing junction [5], a temperature limiting device. [8] The temperature limiting device according to [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 the load heated by the two-wire heater, or a combination thereof. [9] It is a thermal system, A two-wire heater including two terminals, A process controller configured to control the thermal performance of the two-wire heater based on data from one or more discrete sensors, A power switch capable of supplying power to the two-wire heater based on a control signal from the process controller, The process comprises a temperature limiting device separate from the aforementioned process, The modular unit is A heater interface configured to connect to a two-wire heater of the aforementioned thermal system, A power interface configured to be connected to a power source in order to receive power, A controller including a sensor circuit, The sensor circuit is configured to measure the electrical characteristics of the two-wire heater, and the electrical characteristics include voltage, current, or a combination thereof. The controller is configured to calculate the temperature of the thermal system based on the measured electrical characteristics and to determine whether the temperature is higher than the 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 higher than the temperature setpoint. A thermal system comprising the aforementioned temperature limiting device.

[10] The controller of the temperature limiting device stores predefined heater information relating the temperature value of the two-wire heater to measured values ​​of the performance characteristics of the two-wire heater, and the controller is configured to determine the performance characteristics based on the measured electrical characteristics. The thermal system according to [9], wherein the controller is configured to determine, based on the determined performance characteristics and the predefined heater information, the temperature of the thermal system to be the temperature of the two-wire heater, the temperature of the load heated by the two-wire heater, or a combination thereof.

[11] The thermal system described in

[10] , wherein the two-wire heater has a temperature coefficient of resistance that changes, and the performance characteristic is the resistance value at the temperature of the two-wire heater.

[12] The two terminals of the aforementioned two-wire heater include a temperature sensing power pin that defines a temperature sensing junction. The thermal system described in

[10] , wherein the sensor circuit is configured to measure the voltage at the temperature sensing junction, and the performance characteristic is the change in voltage at the temperature sensing junction.

[13] The thermal system described in [9], wherein the temperature limiting device is arranged in parallel with the power switch and detects the electrical characteristics of the heater.

[14] The modular unit comprises the thermal system described in [9], including the power switch.

[15] The aforementioned two-wire heater is an inline heater that heats the fluid flowing through it. The power switch is located on the inline heater and is integrated with the inline heater to transfer heat to the fluid flowing within the inline heater. The thermal system according to [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.

Claims

1. A temperature limiting device for a thermal system, The modular unit is A heater interface configured to connect to a two-wire heater of the aforementioned thermal system, A power interface configured to connect to a power source in order to receive power, An input / output interface configured to communicate with at least one external device, wherein the at least one external device includes a process controller for the thermal system. A power switch electrically coupled between the heater interface and the power interface, A controller including a sensor circuit, The sensor circuit is electrically coupled to the two-wire heater via the heater interface and is configured to measure the electrical characteristics of the two-wire heater, the electrical characteristics including voltage, current, or a combination thereof. A temperature limiting device wherein the controller is configured to calculate the temperature of the thermal system based on the measured change in electrical characteristics and to determine whether the temperature is higher than a temperature setpoint, and the power switch is operated by the controller to control the power to the two-wire heater.

2. The temperature limiting device according to claim 1, wherein 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 higher than the temperature setpoint.

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

4. The temperature limiting device according to claim 3, wherein the resistance-temperature correlation of the two-wire heater changes, and the performance characteristic is the resistance value of the two-wire heater at a certain temperature.

5. The temperature limiting device according to claim 3, wherein the heater interface is connected to the two-wire heater via a temperature sensing power pin that defines a temperature sensing junction in the two-wire heater, the sensor circuit measures the voltage at the temperature sensing junction, and the performance characteristic is the voltage at the temperature sensing junction.

6. The temperature limiting device according to 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 the load heated by the two-wire heater, or a combination thereof.

7. It is a thermal system, A two-wire heater including two terminals, A process controller configured to control the thermal performance of the two-wire heater based on data from one or more discrete sensors, The process controller and a separate temperature limiting device are provided. The temperature limiting device is A heater interface configured to connect to a two-wire heater of the aforementioned thermal system, A power interface configured to be connected to a power source in order to receive power, An input / output interface configured to communicate with the process controller, A power switch electrically coupled between the heater interface and the power interface, A modular unit comprising a controller including a sensor circuit, The sensor circuit is electrically coupled to the two-wire heater via the heater interface and is configured to measure the electrical characteristics of the two-wire heater, the electrical characteristics including voltage, current, or a combination thereof. The controller is configured to calculate the temperature of the thermal system based on the measured change in electrical characteristics and to determine whether the temperature is higher than the temperature setpoint. A thermal system in which 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 higher than the temperature setpoint.

8. The controller of the temperature limiting device stores predefined heater information relating the temperature value of the two-wire heater to measured values ​​of the performance characteristics of the two-wire heater, and the controller is configured to determine the performance characteristics based on the measured electrical characteristics. The thermal system according to claim 7, wherein the controller is configured to determine, based on the determined performance characteristics and the predefined heater information, the temperature of the thermal system to be the temperature of the two-wire heater, the temperature of the load heated by the two-wire heater, or a combination thereof.

9. The thermal system according to claim 8, wherein the resistance-temperature correlation of the two-wire heater changes, and the performance characteristic is the resistance value at the temperature of the two-wire heater.

10. The two terminals of the two-wire heater include a temperature sensing power pin that defines a temperature sensing junction. The thermal system according to claim 8, wherein the sensor circuit is configured to measure the voltage at the temperature sensing junction, and the performance characteristic is the voltage at the temperature sensing junction.

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