Temperature measurement and temperature control integrated self-adaptive temperature control device

Abstract

The invention discloses a self-adaptive temperature control device integrating temperature measurement and temperature control. The self-adaptive temperature control device comprises a power supply module, a heating module and a control module, the power supply module is used for supplying power to the heating module and the control module; the control module is used for measuring and controlling the temperature of the heating module; the heating module is made of a PTC (Positive Temperature Coefficient) heating material; the preparation method of the PTC heating material comprises the following steps: sequentially adding the ethylene-vinyl acetate copolymer and the conductive filler into the molten phase change matrix, uniformly mixing, and carrying out compression molding to obtain the PTC heating material with high thermal cycle stability, the conductive material is a mixture of carbon nanotubes and graphite. According to the invention, the heating sheet made of the PTC heating material with good thermal cycling stability is used as a heating element, and integration of temperature measurement and temperature control is realized through the characteristic that the resistance of the PTC heating material is changed along with the temperature.

Description

Technical Field

[0001] The present invention relates to the technical field of active temperature control of electric heating, and in particular to an adaptive temperature control device integrating temperature measurement and temperature control. Background Art

[0002] In cold climates, low-temperature heating technology is critical for electronic devices. When electronic devices are exposed to extremely low temperatures, their performance will be affected. Some electronic components may fail or their performance may degrade at low temperatures, affecting the normal operation of the device. For example, low temperatures can reduce the performance and life of batteries, and even cause the batteries to not work properly. At the same time, in extremely low temperature environments, some electronic devices may also have cold start problems.

[0003] Heating technology is used to achieve compensatory heating of instruments and equipment under low temperature conditions to ensure the normal operation of the instruments under low temperature conditions. At present, conventional electric heating technology requires the use of temperature sensors, control devices and electric heaters as output elements to form a temperature control loop. This type of electric heating temperature control system has a high temperature control accuracy due to the presence of temperature sensors and control devices, but it needs to occupy the data channel of the control device, affecting the data processing speed of the whole machine. In addition, due to the large number of control feedback links, the system reliability is reduced, and it also leads to greater power consumption and larger size of the temperature control system. Summary of the invention

[0004] Based on the technical problems existing in the background technology, the present invention proposes an adaptive temperature control device that integrates temperature measurement and temperature control. A heating plate made of a PTC heating material with good thermal cycle stability is used as a heating element. The integration of temperature measurement and temperature control is achieved through the characteristic that the resistance of the PTC heating material itself changes with temperature.

[0005] The adaptive temperature control device integrating temperature measurement and temperature control proposed by the present invention comprises a power module, a heating module and a control module; The power supply module is used to supply power to the heating module and the control module; The control module is used to measure and control the temperature of the heating module; The heating module is a PTC heating material; The method for preparing the PTC heating material comprises the following steps: adding ethylene-vinyl acetate copolymer and conductive filler to a molten phase change matrix in sequence, mixing and pressing to obtain a PTC heating material with high thermal cycle stability; The conductive material is a mixture of carbon nanotubes and graphite.

[0006] Preferably, the mass fraction of the phase change matrix is ​​30% to 50%, the mass fraction of ethylene-vinyl acetate copolymer is 30% to 40%, and the mass fraction of the conductive material is 20% to 40%.

[0007] Preferably, the phase change matrix is ​​an organic acid or an alkane substance.

[0008] Preferably, the organic acid is n-decadic acid or n-tetradecanoic acid.

[0009] Preferably, the alkane substance is one of n-hexadecane to n-tetracosane.

[0010] Preferably, the vinyl acetate content in the ethylene-vinyl acetate copolymer is 28-42%.

[0011] Preferably, the mass fraction of carbon nanotubes is 1% to 5%, and the mass fraction of graphite is 15% to 39%.

[0012] Preferably, the melting temperature is 90-100°C.

[0013] Beneficial technical effects of the present invention: The present invention eliminates the controller and temperature sensor required by conventional electric heating systems, does not need to occupy the data channel of the control device, and can use one heating device to replace the three traditional units of heating, temperature measurement and control, thereby reducing the operating weight and communication volume of the temperature control system, and realizing the requirements of electronic equipment for lightweight and high robustness of the temperature control system, greatly reducing the volume of the temperature control system and realizing the lightweight of the temperature control system.

[0014] The PTC heating material of the present invention has good thermal cycle stability, mainly because the conductive filler of the present invention is composed of carbon nanotubes and graphite. When the conductive filler and ethylene-vinyl acetate copolymer are distributed in the molten phase change matrix, a unique "island bridge structure" can be formed inside the phase change matrix. The long carbon nanotubes connect the island structure composed of graphite dispersed in the phase change matrix to form a stable conductive network. Under the joint action of ethylene-vinyl acetate copolymer and phase change matrix, the expansion of the phase change matrix causes the conductive network inside the material to be disconnected during each cycle, that is, the graphite islands are separated from each other, so that the resistance rises sharply. When the temperature decreases, the matrix shrinks so that the graphite islands are connected with the carbon nanotubes to reconstruct a good conductive network, and avoid the phase change matrix and the conductive filler from being greatly offset during the expansion and contraction process, so that the PTC heating material has good thermal cycle stability.

[0015] The present invention, based on the good thermal cycle stability of the PTC heating material, utilizes the characteristic that its own resistance changes with temperature to maintain normal heating power in the low temperature zone. When the temperature reaches the Curie temperature, as the temperature rises, the heating power of the heating device begins to decrease sharply, thereby stabilizing its own temperature between the Curie temperature and the termination temperature, realizing adaptive temperature control. At this time, the own temperature can be calculated by the resistance value, thereby realizing the temperature measurement function. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the temperature resistance characteristics of the PTC heating material proposed in the present invention; Figure 2 This is a thermal cycle curve diagram of the PTC heating material proposed in the present invention. DETAILED DESCRIPTION

[0017] The present invention will be further explained below in conjunction with specific embodiments.

[0018] The relationship between the resistance and temperature of the PTC heating material of the present invention is as follows: (1) In the formula, , , , , , are characteristic parameters of PTC heating materials; The real-time temperature of the PTC heating material; is the Curie temperature of the PTC heating material; is the termination temperature of the PTC heating material; It is the real-time resistance of the PTC heating material.

[0019] Reference Figure 1 , the resistance of the PTC heating material will not change significantly with the increase of temperature before the temperature reaches the Curie point. When the temperature reaches the Curie point, the resistivity of the PTC heating material increases sharply with the increase of temperature until the temperature reaches the termination temperature, at which time the resistivity of the PTC heating material tends to be flat. Due to this characteristic, as shown in formula (2), before the temperature reaches the Curie point, the heating power of the PTC heating material remains stable under a constant voltage. When the temperature reaches the Curie point, the heating power of the PTC heating material decreases sharply with the increase of temperature. Without the help of a control system, the temperature of the PTC heating material can be controlled at a position slightly higher than the Curie point to achieve adaptive temperature control. When the temperature reaches the Curie point, the resistivity of the PTC heating material increases sharply with the increase of temperature until the temperature reaches the termination temperature, at which time the resistivity no longer changes significantly. This part of the area between the Curie temperature and the termination temperature is called the PTC effect occurrence section. Therefore, when the temperature of the heating plate is between the Curie temperature and the termination temperature, the temperature of the heating plate can be calculated based on its resistance value.

[0020] (2) In the formula, for; is the voltage applied to the PTC heating material.

[0021] Example 1 The temperature measurement and temperature control integrated adaptive temperature control device of the present invention comprises a power module, a heating module and a control module, and the heating module is a PTC heating element.

[0022] The preparation method of the PTC heating element is as follows: Take 50g of lauric acid, 30g of EVA, 19g of graphite and 1g of carbon nanotubes, wherein the VA content of EVA is 28%; Place dodecanoic acid in a stirring kettle to melt at 98°C; then add EVA, graphite and carbon nanotubes into the molten phase change matrix in sequence, and stir and mix them evenly under vacuum conditions; The uniformly mixed melt is placed in a mold, pressed and molded at 98°C, and cooled to room temperature to obtain a PTC heating material with good thermal cycle stability.

[0023] The surface of the prepared PTC heating material is coated with a conductive layer to reduce the resistance in the circuit, thereby improving the conductive efficiency of the circuit. The electrode sheets connected with the wires are attached to both sides of the PTC heating material, and then they are wrapped and fixed with insulating tape, thereby making the PTC heating sheet required for the device. Thermal conductive silicone grease is applied to the bottom of the chamber of the box body and the bottom of the cover plate, and then the PTC heating sheet is placed in the chamber of the box body, and then the box body and the cover plate are sealed by laser sealing welding. At this time, the upper part of the PTC heating sheet and the bottom of the cover plate are tightly attached through the thermal conductive silicone grease.

[0024] In a low temperature environment, a fixed voltage is applied to the device, and the Curie point of the PTC heating material used is =38℃, the end temperature is =43℃. , They are 1.2 and -27.2 respectively. Due to the temperature resistance of the PTC heating material itself, the PTC heating plate in the chamber has a higher heating power at low temperatures. When the temperature of the heating plate reaches 38°C, as the temperature rises, the heating power drops sharply. The heating power changes according to its own temperature, and finally the equilibrium temperature of the heating plate stabilizes at 38~43°C. A constant voltage of 15V is applied to the device. When the ambient temperature changes within -10~10°C, the upper surface temperature of the device changes within 38~42°C. During each thermal cycle, since the resistance of the PTC heating material changes with temperature, temperature deviation will occur during the temperature measurement of the PTC heating material. The error between the surface temperature measured by the platinum resistance and the temperature calculated by the resistance value is within 0.2°C.

[0025] In addition, the thermal cycle stability of the PTC heating material was tested by cycling 1, 10, 50, 100, 200 and 400 times. The test results are as follows: Figure 2It can be seen that the resistance-temperature curve of the PTC heating material has not changed significantly after 400 cycles, indicating that the PTC heating material has good thermal cycle stability.

[0026] Example 2 The temperature measurement and temperature control integrated adaptive temperature control device of the present invention comprises a power module, a heating module and a control module, and the heating module is a PTC heating element.

[0027] The preparation method of the PTC heating element is as follows: Take 50g of octadecane, 30g of EVA, 16g of graphite and 4g of carbon nanotubes, wherein the VA content of EVA is 28%; Octadecane is melted in a stirring kettle at 90°C; EVA, graphite and carbon nanotubes are then added to the molten phase change matrix in sequence, and stirred and mixed evenly under vacuum conditions; The uniformly mixed melt is placed in a mold, pressed at 90°C, and cooled to room temperature to obtain a PTC heating material with good thermal cycle stability.

[0028] A conductive film is applied to the surface of the prepared PTC heating material. Electrode sheets connected with wires are attached to both sides of the PTC heating material, and then they are fixed with insulating tape to make the PTC heating sheet required for the device. Thermal conductive silicone grease is applied to the bottom of the chamber of the box body and the bottom of the cover plate, and then the PTC heating sheet is placed in the chamber of the box body, and then the box body and the cover plate are sealed, at which time the upper part of the PTC heating sheet and the bottom of the cover plate are tightly attached through the thermal conductive silicone grease.

[0029] In a low temperature environment, a fixed voltage is applied to the device, and the Curie point of the PTC heating material used =25℃, termination temperature =28℃, and They are 0.9 and -19.9 respectively. Due to the temperature resistance of the PTC heating material itself, the PTC heating plate in the chamber has a higher heating power at low temperatures. When the temperature of the heating plate reaches 25°C, as the temperature rises, the heating power drops sharply. The heating power changes according to its own temperature, and finally the equilibrium temperature of the heating plate stabilizes between 25°C and 28°C. A constant voltage of 10V is applied to the device. When the ambient temperature changes from -20 to 0°C, the upper surface temperature of the device changes from 25 to 28°C. During each thermal cycle, since the resistance of the PTC heating material changes with temperature, temperature deviation will occur during the temperature measurement of the PTC heating material. The error between the surface temperature measured by the platinum resistance and the temperature calculated by the resistance value of the PTC heating material is within 0.5°C.

Claims

1. An adaptive temperature control device integrating temperature measurement and temperature control, characterized in that: It includes a power module, a heating module and a control module; The power supply module is used to supply power to the heating module and the control module; The control module is used to measure and control the temperature of the heating module; The heating module is a PTC heating material; The method for preparing the PTC heating material comprises the following steps: adding ethylene-vinyl acetate copolymer and conductive filler to a molten phase change matrix in sequence, mixing and pressing to obtain a PTC heating material with high thermal cycle stability; The conductive material is a mixture of carbon nanotubes and graphite.

2. The adaptive temperature control device integrating temperature measurement and temperature control according to claim 1, characterized in that: The mass fraction of the phase change matrix is ​​30% to 50%, the mass fraction of ethylene-vinyl acetate copolymer is 30% to 40%, and the mass fraction of the conductive material is 20% to 40%.

3. The adaptive temperature control device integrating temperature measurement and temperature control according to claim 1, characterized in that: The phase change matrix is ​​an organic acid or an alkane substance.

4. The adaptive temperature control device integrating temperature measurement and temperature control according to claim 3, characterized in that: The organic acid is n-decadecanoic acid or n-tetradecanoic acid.

5. The adaptive temperature control device integrating temperature measurement and temperature control according to claim 3, characterized in that: The alkane substance is one of n-hexadecane to n-tetracosane.

6. The adaptive temperature control device integrating temperature measurement and temperature control according to claim 1, characterized in that: The vinyl acetate content in ethylene-vinyl acetate copolymer is 28-42%.

7. The adaptive temperature control device integrating temperature measurement and temperature control according to claim 1, characterized in that: The mass fraction of carbon nanotubes is 1%~5%, and the mass fraction of graphite is 15%~39%.

8. The adaptive temperature control device integrating temperature measurement and temperature control according to claim 1, characterized in that: The melting temperature is 90-100°C.

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