Automatic resistance calibration method and device for preventing dry burning of PI heating film and storage medium

Abstract

The invention relates to an automatic resistance calibration method and device for preventing dry burning of a PI heating film. According to the method, the resistance value of the PI heating film is obtained in real time, whether the resistance value exceeds the preset safety range or not is judged, if yes, the heating control parameters are dynamically adjusted, the resistance value is recovered to be within the safety range, and the dry burning phenomenon is avoided. Meanwhile, according to the method, a resistance change log can be recorded, a resistance change rule can be analyzed, the safety threshold value is dynamically optimized according to environmental factors, the aging degree and the like, and higher adaptability and intelligence are achieved. The method effectively overcomes the defects of a traditional temperature sensor method and a timing protection method, the safety and reliability of the PI heating film are improved, the service life of the PI heating film is prolonged, and the method has wide application prospects.

Description

Technical Field

[0001] This application relates to the field of electrothermal appliance testing, and particularly to a method and apparatus for automatically calibrating the resistance value for preventing dry burning of a PI heating film. Background Art

[0002] Due to its excellent thermal efficiency, uniform heating performance, and good flexibility, PI heating films are widely used in the fields of electronics, medicine, aerospace, etc. However, during long-term operation or under abnormal conditions, the resistance value of PI heating films is prone to change, resulting in overheating or excessively high local temperatures, triggering dry burning phenomena, seriously affecting the service life and reliability of the heating films, and even posing safety hazards.

[0003] Currently, there are mainly two common dry burning protection technologies for PI heating films: one is the over-temperature protection method based on a temperature sensor, which attaches a temperature sensing element to the surface of the heating film to monitor the temperature change in real time and cuts off the power supply when the temperature exceeds a set threshold; the other is the power-off protection method based on time series, which sets a safe working time and forcibly cuts off the power supply when the heating duration exceeds a preset time. However, both of the above methods have certain limitations: the attachment process of the temperature sensor is complex and it is prone to failure due to aging; simple timing protection cannot cope with abnormal changes during the heating process and lacks real-time performance and pertinence.

[0004] These problems restrict the safe use and popularization of PI heating films, and there is an urgent need for a more intelligent and reliable dry burning prevention technology to solve them. Summary of the Invention

[0005] This application adopts a method and apparatus for automatically calibrating the resistance value for preventing dry burning of a PI heating film to solve the above problems.

[0006] A method for automatically calibrating the resistance value for preventing dry burning of a PI heating film includes the following steps: obtaining the real-time resistance value of the PI heating film; determining whether the resistance value exceeds a preset safety threshold; if so, adjusting the heating control parameters for the PI heating film to restore the resistance value to the safe range to avoid the occurrence of dry burning; if not, maintaining the current heating control parameters and continuing to heat the PI heating film.

[0007] By adopting the above technical solution, the dry burning protection of the PI heating film is achieved. This method obtains the resistance value of the heating film in real time, determines whether it exceeds the safe range, and automatically adjusts the heating control parameters when it exceeds, so as to restore the resistance value to the safe level and avoid the occurrence of dry burning. Compared with the traditional temperature sensor method and timing protection method, this method has a faster response and stronger pertinence, can effectively extend the service life of the heating film, and improve its working reliability.

[0008] Further, the step of obtaining the real-time resistance value of the PI heating film includes: passing a constant current through the PI heating film, collecting the voltage at both ends, and calculating the resistance value according to Ohm's law as the current resistance value; and / or, passing a constant voltage through the PI heating film, collecting the passing current, and calculating the resistance value according to Ohm's law as the current resistance value.

[0009] By adopting the above technical solution, the accurate measurement of the resistance value of the PI heating film is achieved. This method provides two ways to obtain the resistance value: one is to pass a constant current and collect the voltage value to calculate the resistance; the other is to pass a constant voltage and collect the current value to calculate the resistance. The combination of the two methods can be flexibly selected under different working conditions, ensuring the accuracy and reliability of the resistance value measurement, and providing a reliable basis for subsequent threshold judgment and parameter adjustment.

[0010] Further, the step of obtaining the real-time resistance value of the PI heating film includes: intermittently stopping the heating of the PI heating film, instead passing a detection current through it, collecting the corresponding voltage value, and calculating the resistance value as the current resistance value; and / or, intermittently stopping the heating of the PI heating film, instead passing a detection voltage through it, collecting the corresponding current value, and calculating the resistance value as the current resistance value.

[0011] By adopting the above technical solution, the coordinated operation of resistance value measurement and heating control is achieved. This method adopts an intermittent resistance value detection method, obtains the resistance value during the interval of stopping heating by periodically inserting short detection periods during the heating process, avoids the interference of continuous heating on the resistance value measurement, and improves the measurement accuracy. At the same time, by reasonably setting the frequency and duration of the detection period, the impact on the heating efficiency can be minimized.

[0012] Further, the step of judging whether the resistance value exceeds the preset safety threshold includes: comparing the current resistance value with the pre-stored upper and lower limits of the safety threshold, and when the resistance value exceeds the upper limit or is lower than the lower limit, it is determined that the safety threshold is exceeded; and / or, comparing the current resistance value with the initial resistance value, and when the change amplitude exceeds the preset ratio, it is determined that the safety threshold is exceeded.

[0013] By adopting the above technical solution, flexible and diverse threshold judgment strategies are achieved. This method can not only compare the current resistance value with the fixed upper and lower limit thresholds, but also compare it with the initial resistance value to judge the relative change amplitude. The two criteria can be used alone or in combination, which can not only detect the absolute abnormality of the resistance value, but also detect the relative abnormality of the resistance value, greatly improving the sensitivity and reliability of the dry burning warning.

[0014] Further, the step of adjusting the heating control parameters of the PI heating film includes: reducing the heating current value until the resistance value returns to the safe range; And / or, reduce the heating voltage value until the resistance value returns to the safe range.

[0015] By adopting the above technical solution, the adaptive adjustment of heating control parameters is achieved. When an abnormal resistance value is detected, the method can make the resistance value return to the safe level by reducing the heating current, voltage, or shortening the heating duration, increasing the heating interval time, etc. A variety of adjustment methods can be flexibly selected according to the actual situation, which can not only quickly cool down but also avoid the adverse effects of sudden temperature drop on the performance of the heating film, realizing flexible and intelligent dry burning protection.

[0016] Further, the step of adjusting the heating control parameters of the PI heating film includes: shortening the heating duration and making the resistance value return to the safe range through intermittent heating; And / or, increasing the heating interval time and making the resistance value return to the safe range through intermittent heating.

[0017] By adopting the above technical solution, the adaptive adjustment of heating control parameters is achieved. When an abnormal resistance value is detected, the method can make the resistance value return to the safe level by reducing the heating current, voltage, or shortening the heating duration, increasing the heating interval time, etc. A variety of adjustment methods can be flexibly selected according to the actual situation, which can not only quickly cool down but also avoid the adverse effects of sudden temperature drop on the performance of the heating film, realizing flexible and intelligent dry burning protection.

[0018] Further, after adjusting the heating control parameters, record the adjusted current value, voltage value, duration, interval time, etc. as the initial parameters for the next heating; And / or, after adjusting the heating control parameters, if the resistance value still fails to return to the safe range after multiple adjustments, trigger an alarm to prompt replacement of the heating film.

[0019] By adopting the above technical solution, the self-learning optimization of heating control parameters is achieved. After each dynamic parameter adjustment, the method records the updated parameter value and uses it as the initial parameter for the next heating. Through continuous iteration, the control parameters gradually tend to be optimal, which not only shortens the adjustment time but also improves the heating efficiency. At the same time, when multiple adjustments cannot make the resistance value return to the safe level, an alarm is triggered in a timely manner to prompt replacement of the heating film in time to avoid accidents.

[0020] Further, the method further includes: recording the resistance value change curve of the PI heating film during the entire working cycle to form a resistance value change log; And / or, analyzing the resistance value change log, extracting the rules and trends of resistance value changes, and optimizing the setting of the safety threshold.

[0021] By adopting the above technical solutions, the full-cycle monitoring of the health status of the heating film is realized. By recording the resistance change curve within the entire working cycle, a complete resistance change log is formed, visually showing the dynamic change process of the resistance of the heating film. By analyzing the laws and trends of the resistance changes, the aging process of the heating film can be accurately grasped, the setting of the safety threshold can be optimized, and a reliable basis can be provided for the maintenance and replacement of the heating film.

[0022] Further, the method further includes: dynamically adjusting the upper and lower limits of the safety threshold according to factors such as environmental temperature and humidity to adapt to different working conditions; and / or, dynamically adjusting the upper and lower limits of the safety threshold according to the aging degree of the PI heating film to adapt to the change of the performance of the heating film.

[0023] By adopting the above technical solutions, the adaptive dynamic adjustment of the safety threshold is realized. The method dynamically adjusts the upper and lower limits of the safety threshold according to factors such as environmental temperature and humidity, as well as the aging degree of the heating film itself. On the one hand, this adjustment can adapt to the changes in the external environment, such as appropriately increasing the threshold upper limit in a high-temperature environment; on the other hand, it also takes into account the attenuation of the heating film performance, such as decreasing the threshold upper limit as the aging degree increases, so as to be closer to the actual working state of the heating film and improve the accuracy of the dry-burning warning.

[0024] A resistance automatic calibration device for preventing dry burning of a PI heating film, further including: a resistance acquisition module for obtaining the real-time resistance of the PI heating film; a resistance judgment module for judging whether the resistance exceeds a preset safety threshold; a control adjustment module for adjusting the heating control parameters of the PI heating film when the resistance exceeds the safety threshold; a data recording module for recording the resistance change curve within the entire working cycle to form a resistance change log; and / or, a parameter setting module for dynamically adjusting the upper and lower limits of the safety threshold according to environmental factors, aging degree, etc.

[0025] By adopting the above technical solutions, the design of a modular and systematic dry-burning prevention device is realized. The device includes multiple functional modules such as resistance acquisition, resistance judgment, control adjustment, data recording, and parameter setting, each performing its own functions and collaborating with each other to form a complete closed-loop control system. The modules are seamlessly connected and data-exchanged through standardized interfaces, which not only ensures the high integration of the system but also has good scalability, providing a basis for the development of intelligence and networking. Brief Description of the Drawings

[0026] Figure 1 is the schematic diagram of the resistance calibration circuit of the PI heating film provided in Embodiment 1 of the present invention; Figure 2 is the schematic diagram of three typical situations of the resistance change of the heating film of the present invention; Figure 3 It is a graph showing the change in resistance values at different positions of the heating film provided by an embodiment of the present invention. Detailed implementation manners

[0027] The following further describes the present application in detail with reference to the accompanying drawings and specific embodiments.

[0028] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, without conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other. Embodiment 1

[0029] This embodiment provides an automatic resistance calibration method for preventing dry burning of a PI heating film, including the following steps: S1: Obtain the real-time resistance value of the PI heating film.

[0030] Specifically, a constant voltage can be applied across the heating film, the current value flowing through it can be collected, and the current resistance value R can be calculated according to Ohm's law U = IR. Or a constant current I can be passed through, the voltage across both ends can be measured, and the resistance value can be calculated according to R = U / I. Figure 1 In the figure, Vin represents the constant input voltage, generally 24V or 48V; R2 is the sampling resistor, and its resistance value should be much smaller than the resistance value R1 of the heating film to avoid interfering with the current sampling, and the typical value is 0.1Ω; U1 is the sampling amplifier, which amplifies the tiny voltage across the sampling resistor R2 to the range acceptable to the ADC (analog-to-digital converter), and the amplification factor is adjustable, generally 10 - 100 times; the ADC converts the amplified analog voltage into a digital quantity, with a resolution usually of 8 - 16 bits and a sampling frequency of 1 - 10kHz; the MCU (microcontroller) reads the current sampling value from the ADC and reads the power supply voltage value from the Vin pin, and substitutes them into the formula to calculate the resistance value R1. To improve the accuracy, multiple samplings can be taken and averaged.

[0031] S2: Determine whether the resistance value exceeds the preset safety threshold.

[0032] Reference Figure 2 、 Figure 3 , the MCU compares the calculated current resistance value with the pre-stored safety threshold. The safety threshold is usually set to 1.2 - 1.5 times the initial resistance value of the heating film at room temperature. When the resistance value exceeds the upper limit, it means that the temperature of the heating film is too high or it has started to age; when the resistance value is lower than the lower limit, it means that the heating film may be short-circuited or partially damaged. In both cases, protection measures need to be taken. Three typical cases of the resistance value change are given: Curve (a) means that the resistance value is always within the safe range, and the heating process can continue; Curve (b) means that the resistance value rises to the dangerous area and then returns to the safe area, and the heating needs to be paused to avoid further deterioration; Curve (c) means that the resistance value continues to rise to the dangerous area, and the heating must be stopped immediately and the heating film needs to be replaced in time.

[0033] S3: If it exceeds the threshold, adjust the heating control parameters.

[0034] When an abnormal resistance value is detected, the MCU controls the power transistor Q1 through PWM (pulse width modulation) to adjust the heating current. By reducing the PWM duty cycle, the heating current can be decreased, causing the temperature of the heating film to drop and the resistance value to return to a safe level. At the same time, the duration t of a single heating can also be shortened on , and the heating interval t on and t off etc. will be recorded as the initial parameters for the next heating, realizing the self-learning optimization of the heating process.

[0035] S4: If it does not exceed the threshold, maintain the current heating control parameters, return to S1, and continue to detect the change in the resistance value. Embodiment 2

[0036] Based on Embodiment 1, this embodiment improves the resistance value detection method. Considering that measuring the resistance value during power-on heating is subject to significant signal interference, this embodiment adopts an intermittent detection method to measure the resistance value during the interval when heating stops, avoiding the influence of the supply current. As Figure 1 、 2 shown, the MCU controls the heating process with a fixed period T = t on + t off . During t on , the PWM signal controls Q1 to conduct, passing a constant current I heat through the heating film; during t off , Q1 is turned off, the heating current stops, and at this time the MCU controls Q2 to conduct, passing a smaller detection current I det into the heating film, while collecting the voltage U det across both ends and calculating the resistance value R det . After the detection is completed, Q2 is turned off, and the next t on cycle starts. In the figure, t det represents the detection time, generally not exceeding 5s, which is much less than t off . The value of T is generally 30 - 120s, which can be determined according to the heat dissipation of the heating film, taking into account both the cooling effect and the detection efficiency. Embodiment 3

[0037] Based on Embodiments 1 and 2, this embodiment adds a dynamic threshold judgment method based on the rate of change of the resistance value. Instead of comparing the current resistance value with a fixed threshold, this method calculates the rate of change relative to the initial value and sets a safety threshold for the rate of change. This can avoid the initial resistance value fluctuations caused by differences in heating film materials and processes, improving the universality of threshold judgment.

[0038] In addition to storing the initial resistance value R ini , the MCU also needs to record the previous resistance value R pre for calculating the change rate dR of the current resistance value R cur : dR = (R cur - R pre ) / R ini × 100%; In the formula, the unit of dR is percentage. In the initial stage of heating (0 - t1), dRth is set to 10% to quickly respond to the sharp change in resistance value; in the middle stage (t1 - t2), dR th linearly decreases to 5% to improve the sensitivity to capture the slow abnormality of the resistance value; in the later stage (after t2), dR th remains 5%, taking into account both the trend of the resistance value of the heating film increasing with aging and avoiding overly frequent alarms. Example 4

[0039] Based on Examples 1 - 3, this example further introduces a temperature compensation factor to adapt to the influence of ambient temperature on the resistance value of the heating film. The resistivity of the PI heating film generally increases with the increase of temperature. For every 10°C increase in temperature, the resistance increases by about 4%. If the room temperature changes greatly, it will distort the change law of the resistance value and interfere with the threshold judgment. Therefore, it is necessary to introduce a temperature correction term when calculating the resistance value to achieve the normalization of the resistance value under different ambient temperatures.

[0040] The formula is: R comp = R meas / [1 + α(T env - T ref )]; In the formula, R comp is the resistance value after temperature compensation, R meas is the measured resistance value, α is the temperature coefficient of resistance of the PI material, and its value is generally between 0.003 - 0.005, Tenv is the current ambient temperature, T ref is the reference temperature, usually taken as 25°C.

[0041] The temperature sensor TS1 is used to collect the ambient temperature near the heating film and send the temperature value to the MCU in real time. The MCU corrects the measured resistance value accordingly to obtain the normalized R comp , and then substitutes it into the subsequent threshold judgment and control adjustment process to ensure the consistency of the dry - burning prevention strategy under different working conditions. TS1 can select common digital temperature sensors, such as DS18B20, with a temperature measurement range of - 55 - 125°C, a resolution of up to 0.0625°C, and communicate with the MCU through a single - wire bus for convenient reading. Example 5

[0042] This embodiment provides a PI heating film anti-dry burning resistance calibration device. Among them, the resistance acquisition module consists of Vin, R2, U1, and ADC, which is responsible for obtaining the resistance value of the PI heating film in real time; the resistance judgment module and the control adjustment module are integrated inside the MCU, and the resistance overrun judgment and the adaptive adjustment of the heating parameters are realized through software algorithms; the data recording module uses the built-in EEPROM (electrically erasable read-only memory) of the MCU, with a capacity of 2 to 32 KB. The data will not be lost after power-off and can permanently save the resistance change log during the heating process, as well as the adjusted PWM parameters, t on 、t off and other historical data; the parameter setting module pre-cures design parameters such as the upper and lower limits of the safety threshold and the temperature compensation coefficient α in the Flash of the MCU, and leaves a remote upgrade interface, which can be dynamically modified wirelessly.

[0043] The whole machine power supply part adopts an AC-DC switching power supply, with an input of 110~220VAC mains power and an output of 24VDC regulated power supply. The maximum output power can reach 100W, and the reliability is high. One path of the 24V power supply is connected to Vin as the working voltage of the PI heating film; the other path is converted to 5V through a DC-DC buck chip to supply power to devices such as the MCU, ADC, and U1. Q1 and Q2 are selected as N-channel enhancement-mode power MOSFETs, with a conduction resistance as low as 10mΩ, a breakdown voltage of 50V, a maximum continuous current of 30A, and a switching frequency of 250kHz, which can meet the large-current control of the heating film.

[0044] All components are mounted on a 4-layer FR-4 epoxy glass cloth printed circuit board, with a size not exceeding 100mm×60mm. The PCB is equipped with overcurrent, overvoltage, and overheat protection circuits, and is equipped with a watchdog timer to prevent the MCU program from running away. The packaging of the components is mainly surface-mounted, which is easy for automated production and assembly. The whole machine is installed in an aluminum casting box, with a volume less than 120mm×80mm×40mm and a weight of less than 500g. The box body is filled with thermal conductive silica gel for heat dissipation of heat-generating components such as the MCU. Embodiment 6

[0045] Based on Embodiment 5, this embodiment expands the functions of the device to achieve remote monitoring and warning. The MCU externally connects a GPRS module through the UART interface to support remote wireless communication. The GPRS module is built with a TCP / IP protocol stack and can upload the heating film status to the cloud server in real time through the Internet. Users can view the resistance change curve, alarm information, etc. of the heating film at any time through a Web browser or a mobile APP to timely control the operation status of the device. The server side uses a MySQL database to store historical data and can generate statistical reports regularly to help analyze the cause of faults and improve the process.

[0046] Meanwhile, an acoustic-optic alarm circuit is also designed in this embodiment. When the MCU detects that the resistance value has exceeded the limit for a long time or the adjustment is ineffective for multiple times, it triggers the GPIO port to output a high level, driving the buzzer BZ and the LED to achieve acoustic-optic alarm, reminding the on-site operator to handle it in time, and notifying the management personnel through GPRS. The alarm information includes the heating film number, position, fault type, treatment suggestions, etc., ensuring that the fault can be traced quickly and the loss is reduced.

[0047] In summary, the PI heating film dry-run prevention resistance calibration method and device provided by the present invention can monitor the change of the heating film resistance value in real time, discover and warn of dry-run faults in time, and achieve online self-repair through closed-loop control, greatly improving the reliability and service life of the PI heating film. The system has a simple structure and low cost, is suitable for industrial mass production, and can be widely applied to various fields where PI heating films are used, such as home appliances, automobiles, and medical devices.

[0048] It should be noted that the specific embodiments described herein can be implemented alone or in any combined manner, as long as the corresponding beneficial effects can be achieved, and they are all within the protection scope of the present invention. The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An automatic resistance calibration method for preventing dry burning of a PI heating film, characterized in that, It includes the following steps: obtaining the real-time resistance value of the PI heating film; judging whether the resistance value exceeds a preset safety threshold; if so, adjusting the heating control parameters of the PI heating film to restore the resistance value within the safe range to avoid dry burning; if not, maintaining the current heating control parameters and continuing to heat the PI heating film.

2. The method according to claim 1, wherein The step of obtaining the real-time resistance value of the PI heating film includes: applying a constant current to the PI heating film, collecting the voltage at both ends, and calculating the resistance value according to Ohm's law as the current resistance value; and / or, applying a constant voltage to the PI heating film, collecting the passing current, and calculating the resistance value according to Ohm's law as the current resistance value.

3. The method according to claim 1, characterized in that, The step of obtaining the real-time resistance value of the PI heating film includes: intermittently stopping heating the PI heating film, instead applying a detection current to it, collecting the corresponding voltage value, and calculating the resistance value as the current resistance value; and / or, intermittently stopping heating the PI heating film, instead applying a detection voltage to it, collecting the corresponding current value, and calculating the resistance value as the current resistance value.

4. The method according to claim 1, wherein The step of judging whether the resistance value exceeds the preset safety threshold includes: comparing the current resistance value with the upper and lower limits of the pre-stored safety threshold, and when the resistance value exceeds the upper limit or is lower than the lower limit, it is determined that the safety threshold is exceeded; and / or, comparing the current resistance value with the initial resistance value, and when the change amplitude exceeds the preset ratio, it is determined that the safety threshold is exceeded.

5. The method according to claim 1, wherein The step of adjusting the heating control parameters of the PI heating film includes: reducing the heating current value until the resistance value is restored within the safe range; and / or, reducing the heating voltage value until the resistance value is restored within the safe range.

6. The method according to claim 1, wherein The step of adjusting the heating control parameters of the PI heating film includes: shortening the heating duration and restoring the resistance value within the safe range through intermittent heating; and / or, increasing the heating interval time and restoring the resistance value within the safe range through intermittent heating.

7. The method according to claim 1, characterized in that, After adjusting the heating control parameters, record at least one of the adjusted current value, voltage value, duration, and interval time as the initial parameter for the next heating; and / or, after adjusting the heating control parameters, if the resistance value still fails to be restored within the safe range after multiple adjustments, trigger an alarm to prompt replacing the heating film.

8. The method according to claim 1, wherein The method further includes: recording the resistance value change curve of the PI heating film during the entire working cycle to form a resistance value change log; and / or, analyzing the resistance value change log to extract the rules and trends of the resistance value change to optimize the setting of the safety threshold.

9. The method according to claim 1, characterized in that The method further includes: dynamically adjusting the upper and lower limits of the safety threshold according to factors such as environmental temperature and humidity to adapt to different working conditions; and / or, dynamically adjusting the upper and lower limits of the safety threshold according to the aging degree of the PI heating film to adapt to the change of the heating film performance.

10. An automatic resistance calibration device for preventing dry burning of a PI heating film, characterized in that, It includes: a resistance value acquisition module for obtaining the real-time resistance value of the PI heating film; a resistance value judgment module for judging whether the resistance value exceeds the preset safety threshold; a control adjustment module for adjusting the heating control parameters of the PI heating film when the resistance value exceeds the safety threshold; a data recording module for recording the resistance value change curve during the entire working cycle to form a resistance value change log; A parameter setting module for dynamically adjusting the upper and lower limits of the safety threshold according to environmental factors, aging degree, etc.

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