A temperature control protection system and method for a heat protection device with a heating tube
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HUIZHOU HUA KAI WEI ELECTRONIC TECH CO LTD
- Filing Date
- 2026-04-21
- Publication Date
- 2026-06-02
Smart Images
Figure CN122138290A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of electric heating temperature control and protection technology, specifically to a temperature control and protection system and method with a built-in thermal protector for the heating element. Background Technology
[0002] Commercial and residential liquid heating equipment typically uses a die-cast metal disc and an encapsulated metal heating element as the core heat source. During operation, precise temperature control and reliable anti-dry-burn protection are fundamental to ensuring safe operation.
[0003] Traditional temperature control and protection systems typically attach temperature sensors to the external working surface of the die-cast metal disc for sampling. When the equipment suddenly loses its external load while heating at full power, the core temperature of the internal metal heating element rises sharply and instantaneously. Due to the large equivalent heat capacity of the die-cast metal disc and the inherent physical hysteresis in heat transfer from the core area to the external surface, the temperature response of the external surface usually lags behind the abrupt change in the actual internal thermodynamic state. This single closed-loop control strategy, which relies on the absolute temperature threshold of the far-field surface, results in the main control circuit detecting an out-of-limit temperature and triggering a power-off command when destructive excess heat has already accumulated inside the heating element. This localized transient high temperature can easily lead to thermal fatigue of the metal tubing and irreversible damage to the internal insulating medium.
[0004] To obtain the true near-field temperature of the heating element and eliminate the aforementioned heat conduction hysteresis, some existing solutions attempt to directly embed the temperature-sensing element and mechanical thermal fuse inside the heating element, co-embedded with the heating wire in insulating magnesium oxide powder. In the manufacturing process of this type of structure, the heating element must undergo multiple tube-shrinking and rolling processes to increase the compaction density of the insulating powder. The intense mechanical compressive stress generated during this process directly acts on the internal sensing and protection elements, easily damaging the ceramic substrate of the temperature-sensing thermistor or causing deformation and jamming of the internal operating mechanism of the mechanical thermal fuse, thus creating a high risk of failure for the safety protection device at the product delivery stage.
[0005] Furthermore, under long-term operation, scale inevitably accumulates on external working surfaces, or the internal heat transfer interface materials undergo natural aging. These physical changes lead to a slow increase in the overall thermal resistance of the system. Conventional control logic only compares instantaneous absolute temperature with a preset fixed threshold in real time, lacking the ability to extract long-term features from temperature and power time-series data. The system cannot effectively identify and provide early warning of this slowly evolving physical interface degradation, causing the equipment to spontaneously extend its high-load heating time under harsh conditions of impeded heat transfer, accelerating the overall aging and failure process of the heating substrate components. Summary of the Invention
[0006] To address the shortcomings of existing technologies, this invention provides a temperature control protection system and method with a built-in thermal protector for heating tubes. This solves the problems in existing heating tube temperature control protection technologies, such as delayed dry-burning response and lack of early warning for long-term heat transfer interface decay caused by relying on the absolute temperature of the far-field surface for control, as well as the vulnerability of the protective element to extrusion stress damage caused by directly embedding it in the insulating powder of the heating tube during tube shrinking.
[0007] To achieve the above objectives, the present invention provides the following technical solution: The first aspect of this invention provides a temperature control protection system with a built-in thermal protector for a heating element, comprising: a heating substrate assembly including a die-cast metal disc and a metal heating element inside, wherein a temperature-sensing blind tube integrally formed inside the die-cast metal disc and conforming to the outer wall of the metal heating element; a near-field composite sensing assembly installed inside the temperature-sensing blind tube, including a thermistor unit and a mechanical thermal fuse unit; a far-field sensing assembly disposed on the outer working surface of the die-cast metal disc; an electric drive assembly including a solid-state relay module and an electrical parameter sampling module connected in series in the power supply circuit; and a main control microprocessor module connected to the near-field composite sensing assembly, the far-field sensing assembly, and the electric drive assembly, for extracting the transient equivalent thermal resistance of the system based on the collected temperature and electric power, performing time-domain separation of the transient equivalent thermal resistance to obtain a slowly changing characteristic parameter characterizing the physical interface decay and a rapidly changing characteristic parameter characterizing the instantaneous heat accumulation rate, performing corresponding level safety control, and performing physical cut-off protection by the mechanical thermal fuse unit when control fails.
[0008] Furthermore, the near-field composite sensing component also includes a probe housing and a high-temperature resistant thermally conductive material. The thermistor unit and the mechanical thermally fused unit are conformally encapsulated within the probe housing via the high-temperature resistant thermally conductive material. The thermistor unit is located at the top of the deepest part of the probe housing, and the mechanical thermally fused unit is axially arranged behind the thermistor unit. The mating gap between the probe housing and the temperature-sensing blind tube is filled with an interfacial thermally conductive medium. This physical structure eliminates the internal air insulation layer, enabling the sensing component and the metal heating element to form a rigid heat transfer continuum without physical breaks, and avoiding damage to internal components caused by mechanical extrusion stress during the manufacturing process of the metal heating element.
[0009] Furthermore, after power-on, the main control microprocessor module performs system initialization, acquiring the initial values of the near-field core temperature and the far-field surface temperature through the thermistor unit and the far-field sensing component. The main control microprocessor module determines whether the system is in cold thermodynamic equilibrium using a steady-state temperature difference threshold model and an absolute cold-state temperature upper limit model, to confirm that there is no residual heat or temperature gradient left over from previous working cycles inside the heating substrate component.
[0010] Furthermore, when the system is determined to be in the cold thermodynamic equilibrium, the main control microprocessor module controls the solid-state relay module to be triggered at the AC zero-crossing point, injecting full-power electrical energy of a preset cycle into the metal heating tube and then turning it off. The main control microprocessor module uses a peak-finding algorithm to locate the time points when the near-field core temperature and the far-field surface temperature reach their transient peak values, calculates the time difference between the two, and extracts the thermal wave delay time constant.
[0011] Furthermore, the main control microprocessor module calculates the transient thermal resistance based on the total injected excitation heat energy and the peak temperature changes in the near and far fields. Using a first-order lumped-parameter thermodynamic model, it decouples the heat wave delay time constant from the transient thermal resistance to calculate the equivalent heat capacity. When the equivalent heat capacity is less than the set safe load heat capacity threshold, the main control microprocessor module locks the solid-state relay module into a dead-zone state. This process extracts intrinsic physical parameters through active thermal excitation, effectively identifying no-load conditions where the external working surface lacks a heat-absorbing medium.
[0012] Furthermore, during the continuous heating phase, the main control microprocessor module acquires the near-field core temperature, the far-field surface temperature, and the instantaneous electrical power. It then calculates the transient equivalent thermal resistance by dividing the transient temperature difference between the near-field core temperature and the far-field surface temperature by the instantaneous electrical power.
[0013] Furthermore, the main control microprocessor module utilizes a low-pass digital filtering algorithm to filter out power frequency interference from the transient equivalent thermal resistance, and inputs the result into a long-period time window definite integral and moving average calculation model for processing to extract the slowly varying characteristic parameters. When the slowly varying characteristic parameters exceed a set physical attenuation threshold, the main control microprocessor module outputs an abnormal status warning signal. This calculation logic filters out short-timescale thermodynamic disturbances, enabling early detection and warning of long-term thermal resistance changes caused by scale deposition or aging of the heat-conducting medium.
[0014] Furthermore, the main control microprocessor module utilizes backward differential operations to construct a first-order time derivative model, performing derivative processing on the transient equivalent thermal resistance between the current sampling period and the previous sampling period to extract the rapidly changing characteristic parameter. When the rapidly changing characteristic parameter exceeds a set step derivative threshold, the main control microprocessor module determines that transient dry burning has occurred and triggers a rapidly changing feedforward cutoff command to disconnect the power supply circuit. This control logic bypasses the conventional absolute temperature closed loop, completing the cutoff operation before the far-field surface temperature exceeds the limit through the abrupt change in the transient equivalent thermal resistance equation.
[0015] Furthermore, the mechanical thermal fuse unit has a fixed physical melting temperature threshold. Under the boundary condition of failure of the main control microprocessor module or the solid-state relay module, when the actual temperature inside the temperature sensing blind tube reaches the physical melting temperature threshold, the mechanical thermal fuse unit generates an irreversible physical circuit break, permanently cutting off the power supply circuit, thereby constructing terminal redundancy protection completely independent of digital algorithms and electronic components.
[0016] The second aspect of this invention provides a temperature control protection method for a heating element with a built-in thermal protector, applied to the temperature control protection system of the aforementioned heating element with a built-in thermal protector, comprising the following steps: synchronously reading the initial values of the near-field core temperature and the far-field surface temperature, and determining whether the system is in cold thermodynamic equilibrium based on a preset condition equation; when the cold thermodynamic equilibrium condition is met, injecting excitation heat energy into the metal heating element, extracting the thermal wave delay time constant and decoupling the equivalent heat capacity, and determining the external load state based on the equivalent heat capacity to block the no-load power supply; during the continuous heating observation phase, based on the real-time temperature and instantaneous... The transient equivalent thermal resistance is calculated based on the electrical power. The transient equivalent thermal resistance is then separated in the time domain to extract slowly changing characteristic parameters reflecting the decay of the physical interface and rapidly changing characteristic parameters reflecting the instantaneous accumulation of heat. Multidimensional safety protection is implemented based on the extracted characteristic parameters. When the rapidly changing characteristic parameter exceeds the set step derivative threshold, a feedforward cutoff command is output to disconnect the power supply circuit. Under the boundary condition of algorithm control logic failure, when the actual temperature inside the temperature-sensing blind tube reaches the physical melting temperature threshold of the mechanical thermal fuse unit, a physical circuit is generated through the mechanical thermal fuse unit to complete the terminal redundancy protection.
[0017] This invention provides a temperature control protection system and method with a built-in thermal protector for the heating element. It has the following beneficial effects: 1. This invention integrates a temperature-measuring blind tube that fits the outer wall of a metal heating element into a die-cast metal disc, and conformally encapsulates the thermistor unit and the mechanical thermal fuse unit within the probe housing using a high-temperature resistant thermally conductive material and places them into the blind tube. This avoids the damage to the internal sensing and protection elements caused by the mechanical extrusion stress generated during the traditional heating element shrinkage manufacturing process, while eliminating the air insulation layer between the element and the tube wall, forming a rigid heat transfer continuum without physical breaks, thus improving the response rate of near-field core temperature acquisition and the reliability of physical fuse protection under extreme conditions.
[0018] 2. This invention calculates transient equivalent thermal resistance based on near-field core temperature, far-field surface temperature, and instantaneous power, and uses differential differentiation to extract rapidly changing characteristic parameters that reflect the instantaneous rate of heat accumulation. This overcomes the hysteresis defect of traditional methods that rely on the absolute temperature threshold of the far field. In the initial stage of local heat accumulation caused by the loss of external load, it can trigger a feedforward cutoff command by identifying the step change in equivalent thermal resistance, and disconnect the power supply circuit before the surface temperature exceeds the limit, thus preventing thermal fatigue and insulation damage to the heat-generating substrate components due to instantaneous dry burning.
[0019] 3. This invention applies low-pass digital filtering, long-period time window integration, and moving average calculation to the transient equivalent thermal resistance, extracting slowly varying characteristic parameters that characterize the decay of the physical interface. It filters out short-timescale thermodynamic disturbances and power frequency interference, accurately separates the long-term increasing trend of heat transfer resistance caused by external scale deposition or internal heat-conducting medium aging, and enables the system to have early detection and warning capabilities for interface physical degradation, avoiding chronic overheating losses caused by long-term operation of heating equipment with defects. Attached Figure Description
[0020] Figure 1 This is a schematic diagram of the physical structure and hardware connection of the present invention; Figure 2 This is a flowchart illustrating the overall workflow of the present invention. Figure 3 This is a control logic diagram of the present invention; Figure 4 This is a multi-parameter time response curve diagram under the instantaneous dry-burning condition of the present invention; Figure 5 This is a graph showing the evolution of slow-change characteristics under the scaling conditions of the present invention. Detailed Implementation
[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0022] See attached document Figure 1 The present invention provides a temperature control protection system with a built-in thermal protector for a heating element. The temperature control protection system includes a heating substrate component, a near-field composite sensing component, a far-field sensing component, an electric drive component, and a main control microprocessor module.
[0023] The heating element assembly provides the system's heat energy and includes a metal heating element and a die-cast metal disc. The metal heating element is filled with insulating magnesium oxide powder and a heating wire. The die-cast metal disc encloses the metal heating element, serving as the physical carrier for heat conduction.
[0024] A near-field composite sensing component is housed within a die-cast metal disc, used to acquire near-end parameters of the heat source and provide basic hardware power-off protection. A temperature-sensing blind tube is integrally formed within the die-cast metal disc, fitting snugly against the outer wall of the metal heating element. The near-field composite sensing component, housed within this blind tube, comprises a thermistor unit and a mechanical thermal fuse unit. The thermistor unit and the mechanical thermal fuse unit are conformally encapsulated within the same probe housing using a high-temperature resistant thermally conductive material. The thermistor unit is used to acquire the near-field core temperature in real time. The mechanical thermal fuse unit is connected in series to the system's main power supply circuit and has a fixed physical melting temperature threshold.
[0025] The wall thickness of the temperature-sensing blind tube is less than that of the conventional die-cast metal disc, creating a low-thermal-resistance heat transfer path. The probe housing is made of a metal material with high thermal conductivity. Axially, the thermistor unit is positioned at the very top of the probe housing, geometrically closest to the high heat flux density center of the metal heating element, ensuring a rapid response of the near-field core temperature to localized transient thermal changes. A mechanical thermal fuse unit is axially positioned behind the thermistor unit. High-temperature resistant thermally conductive material completely fills the voids inside the probe housing, eliminating the air insulation layer between the thermistor unit, the mechanical thermal fuse unit, and the inner wall of the probe housing. After the probe housing is inserted into the temperature-sensing blind tube, the gap between them is further filled with a liquid or paste-like interfacial thermally conductive medium, forming a rigid heat transfer continuum without physical breaks between the metal heating element, the die-cast metal disc, the temperature-sensing blind tube, and the near-field composite sensing component. This side-mounted, independently packaged, and tightly thermally coupled physical topology avoids structural damage to the thermistor unit and the mechanical thermal fuse unit caused by the mechanical extrusion stress generated during the tube shrinking manufacturing process of the metal heating element.
[0026] The far-field sensing component is mounted on the outer working surface of the die-cast metal disc. The outer working surface refers to the physical interface between the heating substrate component and the external load or heating medium. The far-field sensing component is used to acquire the far-field surface temperature in real time.
[0027] The power drive component connects the heating element assembly to the power supply network and includes a solid-state relay module and an electrical parameter sampling module. The solid-state relay module supports AC zero-crossing trigger control and is connected in series in the power supply circuit of the heating element. The electrical parameter sampling module is used to collect voltage and current data of the power supply circuit in real time and calculate the instantaneous power of the system.
[0028] The main control microprocessor module establishes electrical connections with the near-field composite sensing component, the far-field sensing component, and the power drive component. The main control microprocessor module receives temperature and power sampling data and outputs trigger signals to the solid-state relay module according to a preset algorithm logic.
[0029] See attached document Figure 2 In the operation of the temperature control protection system of this embodiment, the main control microprocessor module executes the following processing steps in a time sequence.
[0030] After power-on, the system enters the initialization phase. The main control microprocessor module synchronously reads the initial values of the near-field core temperature and the far-field surface temperature, calculates the temperature difference between them, and determines whether the current system is in thermodynamic cold equilibrium based on the set temperature threshold. At the same time, the main control microprocessor module detects the circuit status through the electrical parameter sampling module to confirm that the mechanical thermal fuse unit is in the conducting state.
[0031] When the system meets the cold equilibrium condition, the main control microprocessor module performs active thermal pulse diagnosis. The main control microprocessor module controls the solid-state relay module to trigger at the AC zero-crossing point, injecting a preset cycle of full-power electrical energy into the metal heating element and then turning it off. Under this pulse excitation, the main control microprocessor module records the time points when the near-field core temperature and far-field surface temperature reach their peak values, extracting the thermal wave delay time constant. Then, combined with the calculated transient thermal resistance, it calculates the equivalent thermal capacity of the interface between the system and the external load. The main control microprocessor module determines the external load status based on the equivalent thermal capacity; if the equivalent thermal capacity is lower than a set lower limit, it triggers a latching command to prohibit subsequent power supply.
[0032] When the system fails to meet the cold equilibrium condition due to active thermal pulse diagnosis, it enters the continuous heating observation phase. The main control microprocessor module controls the solid-state relay module to perform normal power output. During continuous heating, the main control microprocessor module uses real-time acquired near-field core temperature, far-field surface temperature, and instantaneous electrical power to calculate the system's transient equivalent thermal resistance.
[0033] The main control microprocessor module performs time-domain separation processing on the transient equivalent thermal resistance. It calculates the long-period integral moving average of the transient equivalent thermal resistance, using it as a slowly varying characteristic parameter characterizing the long-term decay of the physical interface. Simultaneously, the main control microprocessor module performs first-order time derivative calculation on the transient equivalent thermal resistance, using it as a rapidly varying characteristic parameter characterizing the instantaneous accumulation rate of local heat.
[0034] The main control microprocessor module performs multi-dimensional safety protection based on the separated characteristic parameters. When the slowly changing characteristic parameter exceeds the set physical attenuation threshold, the main control microprocessor module determines that there is a thermal conduction obstacle on the surface of the heating substrate component and outputs a digital warning signal. When the rapidly changing characteristic parameter exceeds the set step derivative threshold, the main control microprocessor module determines that instantaneous dry burning has occurred and directly outputs a feedforward cutoff command to the solid-state relay module to disconnect the power supply circuit.
[0035] Under the boundary condition of the failure of the above algorithm control logic, the internal temperature of the heating substrate component continues to rise. When the actual temperature inside the temperature sensing blind tube reaches the physical melting temperature threshold of the mechanical thermal fuse unit, the mechanical thermal fuse unit undergoes irreversible physical deformation or melting, permanently cutting off the main power supply circuit of the heating tube and completing the terminal redundancy protection of the system.
[0036] After power-on reset, the main control microprocessor module first initializes and configures its internal analog-to-digital conversion peripherals. It then synchronously sends sampling commands to the thermistor unit in the near-field composite sensing component and the far-field sensing component to acquire the initial temperature reference data of the system at time zero. To eliminate electromagnetic interference and white noise at the moment of power-on, the main control microprocessor module performs analog-to-digital conversion on the continuously acquired discrete temperature analog quantities and executes a sliding window mean filtering algorithm. After digital filtering, the main control microprocessor module records the initial value of the near-field core temperature in its internal register. and the initial value of the far-field surface temperature .
[0037] While acquiring initial temperature reference data, the main control microprocessor module performs an integrity check on the basic hardware physical link. The main control microprocessor module detects the voltage difference across the power supply network connected to the metal heating element via a voltage sampling circuit in the power drive component. This step confirms that the mechanical thermal fuse unit connected in series in the main circuit is in a closed conducting state. If a physical open circuit is detected in the main circuit, the main control microprocessor module directly triggers a hardware fault interrupt, blocking the drive port of the solid-state relay module and terminating all subsequent control flows.
[0038] The main control microprocessor module performs a cold-state thermodynamic equilibrium determination based on the acquired initial temperature reference data. The system needs to confirm that there is no residual heat or temperature gradient left over from previous operating cycles inside the heating substrate component. The specific mathematical determination logic requires that two conditional equations be satisfied simultaneously, expressed as follows: ; ; In the above equation, The steady-state temperature difference threshold is the one pre-calibrated by the system. This is the set upper limit for the absolute cold state temperature. The absolute temperature difference condition is used to measure the thermal gradient inside the heating substrate component from the center of the heat source to the external working surface. When the absolute temperature difference is less than or equal to the steady-state temperature difference threshold, it indicates that the heat conduction inside the system has reached static equilibrium. The upper limit for the absolute cold state temperature condition is used to constrain the overall thermophysical energy level of the system, ensuring that the initial bottom temperature of the heating substrate component is within a safe baseline range.
[0039] When the main control microprocessor module determines that both of the above conditional equations are true, the system confirms that it is currently in an ideal cold thermodynamic equilibrium environment. In this state, there is no interference from background heat flow within the heating substrate component, satisfying the physical prerequisite for extracting pure step response characteristics. The main control microprocessor module then configures the trigger timer of the solid-state relay module to guide the system state machine into the active thermal pulse diagnostic phase.
[0040] If the initial temperature reference data fails to simultaneously satisfy the two conditional equations mentioned above, it indicates that the heating substrate component is still in a non-equilibrium state with residual heat. In this non-equilibrium state, the residual nonlinear thermal momentum will severely distort the high-frequency thermal wave signal generated by the active excitation, leading to severe distortion of the subsequently extracted thermal wave delay time constant and equivalent heat capacity data. Simultaneously, injecting a full-power thermal pulse at a relatively high base temperature can easily trigger malfunctions in the mechanical thermal fuse unit. Therefore, under this condition, the main control microprocessor module actively disables the pulse diagnostic enable bit, and the control system skips the active thermal pulse diagnostic stage, directly jumping to the continuous heating observation stage to execute conventional temperature control scheduling.
[0041] See attached document Figure 3 After determining that the system is in cold thermodynamic equilibrium, the main control microprocessor module initiates an active pulse excitation sequence. The main control microprocessor module is configured with an internal hardware zero-crossing detection interrupt to monitor the voltage zero-crossing point of the AC power supply network in the power drive components in real time. Upon capturing the voltage zero-crossing signal, the main control microprocessor module outputs a high-level drive signal to the solid-state relay module, connecting the metal heating element to the power supply network. The internal timer / counter of the main control microprocessor module starts synchronously, and after continuously outputting a preset number of AC half-wave cycles, accurately cancels the drive signal at the next voltage zero-crossing point, forcing the solid-state relay module to turn off.
[0042] This zero-crossing trigger-based control mechanism avoids broadband electromagnetic harmonic interference and transient high-current surges caused by non-zero-crossing switching. The main control microprocessor module acquires voltage and current samples in real time through the electrical parameter sampling module, and measures the pulse duration. Internal integral calculation of the total excitation heat energy injected into the metal heating tube The energy integral operation relationship is expressed as follows: ; in, Indicates the time interval Definite integral operations within; indicating that in The instantaneous electrical power is collected and calculated in real time by the electrical parameter sampling module at any given moment. This represents the time differential variable, used to continuously accumulate instantaneous electrical power over a set time period in the time domain.
[0043] After the solid-state relay module is turned off, a step thermal excitation source is formed inside the heating substrate component, and heat is conducted from the metal heating tube to the external working surface of the die-cast metal disk in the form of a thermal wave. The main control microprocessor module then enables a high-frequency timed sampling interrupt to improve the analog-to-digital conversion sampling rate of the near-field composite sensing component and the far-field sensing component.
[0044] Because the temperature sensing blind tube is in close contact with the outer wall of the metal heating element, the thermistor unit in the near-field composite sensing component is the first to respond to the thermal wave impact. The main control microprocessor module locates the near-field core temperature by comparing the temperature change rate of adjacent sampling periods. The specific moment when the transient peak is reached is recorded as follows: As the heat wave penetrates the die-cast metal disc and reaches the external physical interface, the far-field sensing component responds with a temperature change. The main control microprocessor module uses the same peak-finding algorithm to locate the far-field surface temperature. The moment when the transient peak is reached is recorded as... .
[0045] The main control microprocessor module calculates the time difference between the near-field and far-field temperature peaks and extracts the thermal wave delay time constant, which reflects the overall physical properties of the heating substrate component and the external load. Its mathematical relationship is expressed as: ; After obtaining the thermal wave delay time constant, the main control microprocessor module calculates the peak temperature changes in the near and far fields under pulse excitation, denoted as follows: and The main control microprocessor module calculates the transient thermal resistance of the system under this active pulse excitation based on the extracted temperature difference parameters and the total injected excitation heat energy. The calculation equation is: ; Based on a first-order lumped-parameter thermodynamic model, the system time constant exhibits a linear proportional relationship with the equivalent thermal resistance and equivalent heat capacity. The main control microprocessor module utilizes the extracted thermal wave delay time constant. With transient thermal resistance By decoupling multivariable thermophysical parameters, the current equivalent heat capacity at the interface between the heat-generating substrate component and the external load is calculated.
[0046] ; The main control microprocessor module will decouple the equivalent heat capacity obtained Compared with the safe load thermal capacity threshold pre-stored in non-volatile memory Numerical comparisons were performed. The critical value of safe load thermal capacity characterizes the lower limit of the physical tolerance when the external working surface bears the minimum effective working load.
[0047] If the calculated equivalent heat capacity Less than the critical value of safe load heat capacity The main control microprocessor module determines that the external working surface of the die-cast metal disc lacks an effective heat-absorbing medium, and the system is in a completely unloaded state. In this state, the main control microprocessor module triggers a strong latch-up command, locking the microcontroller output pin of the corresponding solid-state relay module to a low-level dead-zone state. Simultaneously, the main control microprocessor module clears the internal heating request flag, terminating the subsequent operation of the control state machine and preventing the risk of thermal runaway caused by unloaded heating. If the equivalent heat capacity... If the external load is greater than or equal to the critical value of the safe load heat capacity, the main control microprocessor module confirms that the external load status is safe and guides the system to execute the continuous heating observation program.
[0048] After guiding the system into the continuous heating or closed-loop power regulation phase, the main control microprocessor module performs real-time dynamic thermal resistance observation. During full power output or proportional-integral-derivative (PID) control, the absolute temperature of the heating substrate component fluctuates due to nonlinear disturbances from external fluid convection heat transfer. Instead of relying on a single absolute temperature threshold for control definition, the main control microprocessor module extracts intrinsic physical parameters by constructing the system's equivalent thermodynamic equations.
[0049] The main control microprocessor module triggers the analog-to-digital conversion peripheral with a preset control cycle to synchronously read the near-field core temperature output by the near-field composite sensing component. Far-field surface temperature output by the far-field sensing component The real-time values are displayed. Simultaneously, the main control microprocessor module reads the instantaneous power of the current power supply circuit through the power drive component. The main control microprocessor module calculates the system's current transient equivalent thermal resistance by dividing the transient temperature difference between the near and far fields by the instantaneous electrical power. Its mathematical expression is: ; To separate the thermodynamic characteristics under different physical decay periods, the main control microprocessor module performs transient equivalent thermal resistance analysis. A dual-channel data stream separation is performed in the time domain. The main control microprocessor module allocates a long-period data buffer queue in its internal random access memory to record the historical operating trajectory of the transient equivalent thermal resistance. The main control microprocessor module applies a low-pass digital filtering algorithm to the equivalent thermal resistance data in the buffer queue to filter out power frequency interference and high-frequency thermal noise caused by grid voltage fluctuations and external fluid boiling. Subsequently, the main control microprocessor module introduces a long-period time window. The filtered data is subjected to definite integral and moving average operations to extract the slowly varying characteristic parameters of the system. The operational relationship is expressed as: ; in, This represents the normalization coefficient used to average the cumulative integral results over a long-period time window. Indicates the long-period time window interval Definite integral operations performed internally; Indicates the system in the integral variable The transient equivalent thermal resistance at the corresponding moment is usually the effective thermal resistance value after filtering out power frequency interference using a low-pass digital filtering algorithm. This represents the time differential variable, used for continuous time-domain accumulation of transient equivalent thermal resistance within a long-period time window.
[0050] Slowly varying characteristic parameters filter out short-term thermodynamic disturbances, reflecting long-term changes in thermal impedance of the internal heat-conducting medium or external physical interface of the heating substrate component. The main control microprocessor module uses this parameter as the basic physical basis for observing scale deposition or thermal grease aging. In the parallel channel of slow-varying feature extraction, the main control microprocessor module performs differential operations on the transient equivalent thermal resistance. The main control microprocessor module calculates the difference between the transient equivalent thermal resistance of the current sampling period and the transient equivalent thermal resistance of the previous sampling period, and divides it by the sampling time interval of the control period. Through this backward differential algorithm, the main control microprocessor module performs first-order time derivative of the transient equivalent thermal resistance to extract the fast-varying characteristic parameters of the system. Its mathematical expression is: ; The rapidly changing characteristic parameters reflect the transient step rate of the system's equivalent thermal resistance in the time domain. When the external workload is momentarily lost, the near-field core temperature response is rapid while the far-field surface temperature response exhibits physical hysteresis, instantly disrupting the equilibrium state of the transient equivalent thermal resistance equation. The main control microprocessor module extracts the rapidly changing characteristic parameters to establish a digital model observing the instantaneous local heat accumulation rate, providing anti-dry-burning data input unaffected by voltage fluctuations for the subsequent multi-dimensional safety control state machine.
[0051] See attached document Figure 1 - Appendix Figure 3 The main control microprocessor module constructs a state machine control matrix with four safety levels based on the slowly changing and rapidly changing characteristic parameters extracted during the continuous heating stage. The main control microprocessor module evaluates the numerical range of the characteristic parameters in real time to determine whether the system is in a steady-state closed-loop maintenance, slowly changing attenuation warning, rapidly changing feedforward cutoff, or physical bottom-line protection state.
[0052] When the rapidly changing characteristic parameter is within the dead zone of the zero-point neighborhood and the slowly changing characteristic parameter does not exceed the preset physical attenuation threshold, the main control microprocessor module determines that the system's heat conduction path is unobstructed and the external load is in a normal heat absorption state. In this state, the main control microprocessor module maintains steady-state closed-loop control logic. The main control microprocessor module adjusts the duty cycle of the pulse width modulation signal output to the solid-state relay module in real time based solely on the difference between the far-field surface temperature and the user-set target temperature, using its internal proportional-integral-differential algorithm, to maintain a constant temperature on the external working surface.
[0053] During long-term operation or heat preservation, the main control microprocessor module continuously monitors the evolution trajectory of slowly changing characteristic parameters. When the rapidly changing characteristic parameters remain stable, but the slowly changing characteristic parameters exceed the preset physical attenuation threshold, it indicates that scale deposits exist on the external working surface of the heating substrate component, or that the internally encapsulated thermal interface material has aged and dried out. This physical degradation leads to an increase in the overall thermal resistance of the system. The main control microprocessor module records this physical interface attenuation state in its internal registers and outputs an abnormal status warning signal to the external display module or host computer through the peripheral serial communication interface. This slowly changing attenuation warning logic belongs to the maintenance prompt level. The main control microprocessor module will not cut off the drive signal of the solid-state relay module, nor interrupt the current power supply and heating process, to ensure that the basic heating function of the system is not affected under slight thermal resistance degradation conditions.
[0054] When the external workload is suddenly lost during continuous heating, such as when the heating medium completely evaporates or the heated container is displaced, the far-field surface temperature of the heating substrate component responds slowly due to the thermal inertia of the die-cast metal disc. The near-field core temperature rises sharply due to the loss of the external heat dissipation end. This nonlinear thermodynamic abrupt change leads to a breakdown in the equilibrium of the transient equivalent thermal resistance equation, reflected in a sharp positive step jump in the fast-changing characteristic parameter. Once the main control microprocessor module detects that the fast-changing characteristic parameter exceeds the set step derivative threshold within a single sampling period, the main control microprocessor module determines that the system has experienced a transient dry-burning condition. The main control microprocessor module immediately bypasses the conventional temperature closed-loop logic and triggers a fast-changing feedforward cutoff command. The main control microprocessor module sets the control pin of the solid-state relay module to a low-level dead zone state, forcibly disconnecting the main power supply circuit to prevent insulation damage or metal fatigue of the heating substrate component due to instantaneous localized heat accumulation.
[0055] Under extreme hardware failure boundary conditions, the system possesses an ultimate physical redundancy protection mechanism that allows it to operate independently of the digital control loop. When the silicon wafer inside the solid-state relay module experiences physical breakdown, causing the high-voltage power supply circuit to remain open, or when the main control microprocessor module is paralyzed by external strong electromagnetic interference, the aforementioned software algorithm based on feature parameter extraction and the electronic switch execution logic will all fail. At this time, the heating substrate component is in a completely uncontrolled, full-power heating state, with the internal temperature continuously rising. Because the mechanical thermal fuse unit is encapsulated inside the temperature sensing blind tube attached to the outer wall of the metal heating tube, it is directly exposed to the high heat flux density near-field core region. When the actual physical temperature inside the temperature sensing blind tube reaches the fixed melting temperature threshold of the mechanical thermal fuse unit, the bimetallic strip or fusible alloy inside the mechanical thermal fuse unit directly activates, generating an irreversible physical circuit break. This circuit break permanently cuts off the high-voltage main power supply circuit of the heating tube at the physical level, completing terminal disaster-level protection independent of any software algorithm and low-voltage electronic devices, eliminating the safety hazard of thermal runaway in the system.
[0056] Specific application examples: To further illustrate the practical engineering application effect of the temperature control protection system of this invention, the following detailed description is based on a specific implementation scenario using a cast aluminum heating plate in a 2000W commercial liquid heating device, and comparative experimental data is introduced to verify the technical control advantages of this solution. In this application scenario, the heating substrate component adopts a die-cast metal plate with a diameter of 180mm, and the rated electrical power of the metal heating tube is calibrated to 2000W. The wall thickness of the temperature sensing blind tube is controlled at 1.5mm, the physical melting temperature threshold of the mechanical thermal fuse unit inside the near-field composite sensing component is selected as 250℃, and the critical value of the safe load heat capacity is set to the thermodynamic parameters corresponding to 500 ml of water equivalent.
[0057] See attached document Figure 4 This figure illustrates the transient physical evolution of the system under continuous full-power operation when the external workload is suddenly lost. The experiment was set to trigger a forced evacuation and dry-burning condition at the 50th second of normal boiling operation. Under the traditional control strategy relying on a single absolute temperature threshold, the system needs to wait for the far-field surface temperature to reach the preset absolute danger threshold before executing the power-off command. Due to the inherent heat transfer time constant delay of the die-cast metal disc, severe heat accumulation occurs on the surface and inside of the metal heating element in the interval from the 50th second until the far-field surface temperature exceeds the limit. Local transient temperature overshoot can easily lead to irreversible physical oxidation of the heating material.
[0058] Combined with appendix Figure 4By comparing the extracted rapid-change characteristic parameter curves, the main control microprocessor module of this system continuously calculates the transient equivalent thermal resistance and performs first-order time derivative calculation during full-power heating. At the moment the external load is lost at 50 seconds, the far-field heat dissipation boundary conditions change abruptly, and the steady-state equilibrium of the transient equivalent thermal resistance equation is broken. Observational data shows that the rapid-change characteristic parameter curve exhibits a steep positive step at 51.5 seconds, exceeding the set step derivative threshold, and the main control microprocessor module then outputs a feedforward cutoff command. Experimental results show that this method reduces the identification and cutoff response time of the instantaneous dry-burning state from more than 12 seconds in the traditional method to less than 1.5 seconds. This feedforward cutoff mechanism intercepts the initial thermal runaway trend of heat diffusion from the heat source to the periphery, effectively avoiding thermal fatigue caused by rapid heat accumulation in the metal substrate.
[0059] See attached document Figure 5 The figure illustrates the degradation trajectory of the physical interface thermal conductivity impedance after hundreds of heating cycles. The experiment simulated the long-term evaporation of hard water containing calcium carbonate and magnesium carbonate on the external working surface. Under traditional control methods, the main control microprocessor module only monitors the far-field surface temperature to maintain a normal closed loop, and the system automatically compensates for the decrease in heat transfer efficiency by extending the heating time. Under this condition, the equipment operates under high load with inherent defects for extended periods, leading not only to increased energy consumption but also to the potential for chronic overheating damage to the bottom of the heating plate due to the accumulated interfacial thermal resistance.
[0060] Combined with appendix Figure 5 The system's main control microprocessor module uses a long-cycle time window to perform integral moving average processing on the transient equivalent thermal resistance, filtering out high-frequency temperature change interference generated during single water injection or boiling phases. Continuous observation curves show that as the full-load heating cycle accumulates, the thickness of the scale deposit on the external working surface gradually increases, and the slowly varying characteristic parameter exhibits a smooth increasing trend. When the test reaches the 300th heating cycle, the slowly varying characteristic parameter value crosses the preset physical attenuation threshold. At this data node, the main control microprocessor module accurately outputs a digital warning signal, indicating the presence of heat transfer obstruction on the external working surface. This mechanism, through pure digital filtering and algorithmic calculation, achieves early detection and warning of interface degradation of the heating substrate, enabling the system to possess the ability to perceive the physical state during long-cycle operation.
Claims
1. A temperature control protection system with a built-in thermal protector for a heating element, characterized in that, include: The heating substrate assembly includes a die-cast metal disc and an internal metal heating tube, wherein a temperature measuring blind tube is integrally formed inside the die-cast metal disc and fits the outer wall of the metal heating tube. A near-field composite sensing component is installed inside the temperature measuring blind tube and includes a thermistor unit and a mechanical thermal fuse unit. A far-field sensing component is disposed on the outer working surface of the die-cast metal disc. The power-driven component includes a solid-state relay module and an electrical parameter sampling module connected in series in the power supply circuit; The main control microprocessor module is connected to the near-field composite sensing component, the far-field sensing component, and the electric power drive component, respectively. It is used to extract the transient equivalent thermal resistance of the system based on the collected temperature and electric power, perform time-domain separation on the transient equivalent thermal resistance to obtain a slowly changing characteristic parameter characterizing the physical interface decay and a rapidly changing characteristic parameter characterizing the instantaneous heat accumulation rate, execute the corresponding level of safety control, and perform physical cut-off protection by the mechanical thermal fuse unit when the control fails.
2. The temperature control protection system with a built-in thermal protector for a heating element according to claim 1, characterized in that, The near-field composite sensing component also includes a probe housing and a high-temperature resistant thermally conductive material. The thermistor unit and the mechanical thermal fuse unit are conformally encapsulated inside the probe housing through the high-temperature resistant thermally conductive material. The thermistor unit is located at the top of the deepest part of the probe housing, and the mechanical thermal fuse unit is arranged axially behind the thermistor unit. The interfacial thermally conductive medium is filled in the mating gap between the probe housing and the temperature measuring blind tube.
3. The temperature control protection system with a built-in thermal protector for the heating element according to claim 1, characterized in that, After power-on, the main control microprocessor module performs system initialization and obtains the initial values of the near-field core temperature and the far-field surface temperature through the thermistor unit and the far-field sensing component. The main control microprocessor module determines whether the system is in cold thermodynamic equilibrium by using a steady-state temperature difference threshold model and an absolute cold temperature upper limit model.
4. The temperature control protection system with a built-in thermal protector for the heating element according to claim 3, characterized in that, When the system is determined to be in the cold thermodynamic equilibrium, the main control microprocessor module controls the solid-state relay module to be triggered at the AC zero-crossing point, injecting full-power electrical energy of a preset cycle into the metal heating tube and then turning it off; The main control microprocessor module uses a peak-finding algorithm to locate the time points when the near-field core temperature and the far-field surface temperature reach their transient peak values, calculates the time difference between the two, and extracts the thermal wave delay time constant.
5. A temperature control protection system with a built-in thermal protector for a heating element according to claim 4, characterized in that, The main control microprocessor module calculates the transient thermal resistance based on the total injected excitation heat energy and the peak temperature changes in the near and far fields, and uses a first-order lumped parameter thermodynamic model to decouple the thermal wave delay time constant from the transient thermal resistance to calculate the equivalent heat capacity. When the equivalent heat capacity is less than the set safe load heat capacity threshold, the main control microprocessor module locks the solid-state relay module into a dead zone state.
6. The temperature control protection system with a built-in thermal protector for a heating element according to claim 1, characterized in that, During the continuous heating phase, the main control microprocessor module acquires the near-field core temperature, the far-field surface temperature, and the instantaneous electrical power. It then calculates the transient equivalent thermal resistance by dividing the transient temperature difference between the near-field core temperature and the far-field surface temperature by the instantaneous electrical power.
7. The temperature control protection system with a built-in thermal protector for a heating element according to claim 1, characterized in that, The main control microprocessor module uses a low-pass digital filtering algorithm to filter out power frequency interference from the transient equivalent thermal resistance, and inputs it into a long-period time window definite integral and moving average calculation model for processing to extract the slowly varying characteristic parameters. When the slowly varying characteristic parameter exceeds the set upper limit of the physical attenuation threshold, the main control microprocessor module outputs an abnormal status warning signal.
8. A temperature control protection system with a built-in thermal protector for a heating element according to claim 1, characterized in that, The main control microprocessor module uses backward differential operation to construct a first-order time derivative operation model, performs derivative processing on the transient equivalent thermal resistance of the current sampling period and the previous sampling period, and extracts the fast-changing characteristic parameters. When the rapid change characteristic parameter exceeds the set step derivative threshold, the main control microprocessor module determines that instantaneous dry burning has occurred and triggers a rapid change feedforward cutoff command to disconnect the power supply circuit.
9. A temperature control protection system with a built-in thermal protector for a heating element according to claim 1, characterized in that, The mechanical thermal fuse unit has a fixed physical melting temperature threshold. Under the boundary condition of failure of the main control microprocessor module or the solid-state relay module, when the actual temperature inside the temperature sensing blind tube reaches the physical melting temperature threshold, the mechanical thermal melting unit generates an irreversible physical circuit break, permanently cutting off the power supply circuit.
10. A temperature control protection method for a heating element with a built-in thermal protector, characterized in that, A temperature control protection system applied to the built-in thermal protector of the heating element according to any one of claims 1-9, comprising the following steps: The initial values of the near-field core temperature and the far-field surface temperature are read simultaneously, and the system is determined to be in cold thermodynamic equilibrium by combining the preset condition equations. When the cold-state thermodynamic equilibrium condition is met, excitation heat energy is injected into the metal heating tube, the thermal wave delay time constant is extracted and the equivalent heat capacity is decoupled, and the external load state is determined according to the equivalent heat capacity to block the no-load power supply. During the continuous heating observation phase, the transient equivalent thermal resistance is calculated based on real-time temperature and instantaneous electric power. The transient equivalent thermal resistance is then subjected to time-domain separation processing to extract the slowly changing characteristic parameters reflecting the decay of the physical interface and the rapidly changing characteristic parameters reflecting the instantaneous accumulation of heat. Multidimensional safety protection is implemented based on the extracted feature parameters. When the rapidly changing feature parameters exceed the set step derivative threshold, a feedforward cutoff command is output to disconnect the power supply circuit. Under the boundary condition of algorithm control logic failure, when the actual temperature inside the temperature measuring blind tube reaches the physical melting temperature threshold of the mechanical thermal fuse unit, the mechanical thermal fuse unit generates a physical circuit to complete the terminal redundancy protection.