A method for measuring temperature of an induction heating element

Abstract

The present invention provides a temperature measurement method for an induction heating element, which comprises the following steps: A. a modulation module modulates the output voltage of a power supply into a PWM waveform voltage through pulse width modulation, and applies it to an induction coil. When the PWM waveform voltage V≠0, the induction coil heats the induction heating element, and the thermoelectromotive force signal generated by the induction heating element after being heated is transmitted to a controller; B. the modulation module also transmits the PWM waveform voltage signal to the controller; C. during the period when the PWM waveform voltage V=0, the controller records the thermoelectromotive force value generated by the induction heating element after being heated and calculates the temperature value accordingly; the induction heating element comprises thermocouples with different metal materials, wherein at least one metal material is an electromagnetic receptor. The present invention solves the problem that the induction heating element is not easy to fix in a small space temperature measurement environment and that the induction potential interference voltage is generated when the thermocouple contact surface is measured.

Description

Technical Field

[0001] The invention belongs to the technical field of electromagnetic induction heating and temperature measurement sensing, and in particular relates to a temperature measurement method of an induction heating element. Background Art

[0002] Electromagnetic induction heating tobacco is a new type of heating tobacco. Compared with the resistance heating method, electromagnetic induction heating has the characteristics of high energy conversion efficiency, fast heating temperature rise, and diversified layout of induction heating elements. At the same time, the material heating position also has good uniformity and high accuracy. The heating structure of the existing electromagnetic heating technology for heating cigarettes is mostly composed of an induction coil and an induction heating element. The induction coil is wound around the outside of the induction heating element. The heating element is heated by the principle of electromagnetic induction, and then the heated cigarette is heated by the induction heating element. The smoking taste of the heating tobacco with this structure is closely related to the heating element inside the tobacco. Generally, the temperature of the internal heating element needs to reach about 350℃ for the tobacco to have the best taste. Therefore, its core element is the induction heating element, and the core technology is the temperature control of the induction heating element. The key to temperature control is to measure the temperature. Since the heating element in the smoking device is placed in the heating cavity, the space inside the heating cavity is small. Secondly, the outer shell of the heating cavity is made of PEEK material, which is opaque. The temperature measurement of the induction heating element in the smoking device is blocked by the heating cavity shell of the smoking device, the surrounding coil, etc., which becomes a technical difficulty.

[0003] The above electromagnetic induction heating cigarette smoking device has a particular principle and structure, which makes the measurement technology of the surface temperature of the induction heating element different from the traditional resistance heating element surface temperature measurement technology. The resistance heating element can be exposed to the air without any shielding, and its surface temperature can be measured by an infrared thermal imager, or by a contact temperature sensor such as a thermocouple. The induction heating element of the electromagnetic induction heating cigarette smoking device is not exposed to the air because it is surrounded by an induction coil, and its surface temperature cannot be measured by an infrared thermal imager. When using traditional thermocouples to conduct temperature tests on electromagnetic induction heating smoking devices, the temperature measuring end of the thermocouple needs to be in close contact with the surface of the induction heating element. However, this method will cause a potential difference at each point of the induction heating element parallel to the direction of the current, thereby introducing an interfering potential. At the same time, when the thermocouple measures the surface temperature of the induction heating element, the temperature measurement environment in which it is located has an alternating magnetic field. Therefore, it is affected by the alternating magnetic field. Since the loop of the thermocouple lead wire is in a changing magnetic field, the closed loop generates an induced potential, which affects the accuracy of the thermocouple temperature measurement. Inaccurate temperature measurement makes it difficult to ensure the quality of the smoking device.

[0004] In order to solve the above problems, the present invention is proposed. Summary of the invention

[0005] In order to solve the above technical problems, the specific technical solution of a temperature measurement method of an induction heating element of the present invention is as follows:

[0006] A method for measuring temperature of an induction heating element comprises the following steps:

[0007] A. The modulation module modulates the output voltage of the power supply into a PWM waveform voltage through pulse width modulation and applies it to the induction coil. When the PWM waveform voltage V≠0, the induction coil heats the induction heating element, and the thermoelectromotive force signal generated by the induction heating element after being heated is transmitted to the controller;

[0008] B. The modulation module also transmits the PWM waveform voltage signal to the controller;

[0009] C. During the period when the PWM waveform voltage V=0, the controller records the thermoelectromotive force value generated by the induction heating element after being heated and calculates the temperature value accordingly;

[0010] The induction heating element comprises a thermocouple having different metallic materials, wherein at least one metallic material is an electromagnetic receptor.

[0011] Preferably, the cold end of the induction heating element is connected in parallel with a cold end compensation resistor R Cu , the cold end compensation resistor R Cu The resistance value is set to the corresponding resistance value R0 when the temperature is 0℃ to compensate for the cold end temperature.

[0012] Preferably, the different metal materials are selected from Permalloy, Constantan alloy or Iron-Ni alloy.

[0013] Preferably, the cold end compensation resistor R Cu The resistance of pure metal material.

[0014] Preferably, the cold end compensation resistor R Cu The measurement method of the corresponding resistance R0 at a temperature of 0°C is as follows:

[0015] Z1. The hot end of the temperature-sensitive heating element is placed in a constant temperature heating furnace 9, the cold end is led out with a copper wire, and the cold end is placed in an oil bath 12;

[0016] Z2. The measuring device is connected in series with the ammeter 14, and then connected in parallel with the sliding rheostat 15, and both ends of the parallel circuit are connected to the cold end of the temperature-sensing heating element;

[0017] Z3. Control the temperature in the constant temperature heating furnace 9, adjust the cold end temperature in the range of 0-50 ℃, and measure the resistance value R of the sliding rheostat 15 with a resistance box t , according to the linear characteristic of resistance changing with temperature R t=R0(1+αt), α and R0 are calculated, where α is the temperature coefficient of resistivity.

[0018] Preferably, the cold end compensation resistor R Cu is a copper resistor.

[0019] Preferably, the temperature in the constant temperature heating furnace 9 is 300-400°C.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The induction heating element in the electromagnetic induction heating smoking device of the present invention is composed of different metal materials, among which at least one metal material is an electromagnetic receptor, which can not only perform induction heating, but also reflect temperature information through the thermoelectric potential generated by itself. This structure that can both generate heat and measure temperature solves the problem that thermocouples are difficult to fix in a small space temperature measurement environment and that induced potential interference voltage is generated when measuring temperature on the contact surface of the thermocouple.

[0022] 2. Utilizing the principle of pulse width modulation (PWM), the induction coil is used to perform induction heating on the induction heating temperature measuring element during the period when the PWM waveform voltage V≠0, and the temperature of the induction heating element is measured during the period when the PWM waveform voltage V=0. The thermoelectric potential value of the induction heating temperature measuring element is recorded by the controller, and the temperature value is calculated based on it to obtain the surface temperature of the induction heating temperature measuring element. Since there is no current in the coil during the period when V=0, there is naturally no electromagnetic field, which solves the problem of induced potential caused by electromagnetic interference in the alternating magnetic field temperature measurement environment, so that accurate temperature measurement can be achieved in semi-enclosed small spaces and temperature measurement environments with alternating magnetic fields.

[0023] 3. The present invention connects a metal resistor in parallel to the cold end of the induction heating element. The resistance of the metal resistor is the resistance corresponding to a temperature of 0°C, which solves the problem of temperature measurement error caused by cold end temperature change when measuring the temperature of the induction heating element in the electromagnetic induction heating smoking device. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the thermocouple schematic diagram;

[0025] Figure 2 Schematic diagram of an induction heating element made of two different metal materials;

[0026] Figure 3 This is a schematic diagram of converting a sine wave into a PWM wave;

[0027] Figure 4 This is a schematic diagram of PWM temperature measurement;

[0028] Figure 5 This is a schematic diagram of the cold-end compensation principle;

[0029] Figure 6 This is a schematic diagram of the measurement method of the cold-end compensation resistor;

[0030] Description of reference numerals:

[0031] 9-constant temperature heating furnace, 10-insulation cotton, 11-induction heating element, 12-oil bath, 13-resistance R 测 , 14-ammeter, 15-sliding rheostat, 16-test tube. DETAILED DESCRIPTION

[0032] In order to better understand the purpose, structure and function of the present invention, a temperature measurement method of a heating smoking device of the present invention is further described in detail below with reference to the accompanying drawings.

[0033] The induction heating element of the present invention is a thermocouple composed of two different metal materials, wherein at least one metal material is an electromagnetic receptor, which can be inductively heated and can reflect temperature information through the thermoelectric potential generated by itself. The magnitude of the thermoelectric potential is determined by the temperature difference between the cold end and the hot end, and has nothing to do with the thickness of the two metal conductors, but only with the characteristics of the two metal conductors and the temperature of the two ends. The available relationship expression is E t =E AB (T2, T1), where E t is the thermoelectric potential, T1 is the cold end temperature, and T2 is the hot end temperature. If T1 remains basically constant, then E t As the hot end temperature T2 changes, measure E t The hot end temperature T2 can be measured.

[0034] The principle of cold junction compensation of induction heating elements is:

[0035] A cold end compensation resistor is connected in parallel to the cold end of the induction heating element to compensate the cold end;

[0036] Specifically: connect a cold end compensation resistor R in parallel to the cold end of the induction heating element Cu , choose metal resistor as cold end compensation resistor R Cu , the thermoelectric potential E of the induction heating element t It can be equivalent to the power supply E and the power supply internal resistance r0, and the thermoelectric potential E can be measured. t The device is equivalent to a resistor R 测 According to Kirchhoff's current law, the current I flowing from the equivalent power source E through the internal resistance r0 is equal to the current flowing through the metal resistance R Cu The current I1 flows through the measuring device resistor R 测 The formula is: I = I1 + I2, which can be written as I2 = I-I1, where I is the current flowing out of the equivalent power supply E through the internal resistance r0, and I1 is the current flowing through the cold end compensation resistor RCu The current, I2, flows through the measuring device resistor R 测 The current. According to the thermocouple intermediate temperature law: E t =E AB (T2, T1) = E AB (T2, 0)-E AB (T1, 0), the cold end temperature T1 increases, then E AB (T1, 0) increases, the thermoelectric potential E t The equivalent power source E and current I also decrease. Assume that the reduction of current I is ΔI; the cold end compensation resistor R Cu At the same temperature as the cold end, the cold end temperature T1 increases, and the resistance R Cu Increases, flows through R Cu The current I1 decreases accordingly, then I2 = (I-ΔI)-(I1- ΔI1), and I2 = (I-I1)-(ΔI-ΔI1); the cold end compensation resistor R Cu The resistance value is adjusted to the resistance value R0 corresponding to the temperature of 0℃, so that the current change ΔI≈ΔI1 caused by the change in cold end temperature, then when the cold end temperature T1 increases, I2=I-I1, thus realizing compensation for the cold end temperature.

[0037] Keep the cold end of the induction heating element away from the heat source, that is, the hot end of the induction heating element.

[0038] A temperature measurement method of an induction temperature measuring element of the present invention comprises the following specific steps:

[0039] A. The modulation module of the electromagnetic induction heating smoking device modulates the output voltage of the power supply into a PWM waveform voltage through pulse width modulation, and applies it to the induction coil of the electromagnetic induction heating smoking device. When the PWM waveform voltage V≠ 0, the induction coil heats the induction heating element, and the thermoelectromotive force signal generated by the induction heating element after being heated is transmitted to the controller;

[0040] B. The modulation module also transmits the PWM waveform voltage signal to the controller;

[0041] C. During the period when the PWM waveform voltage V=0, the controller records the thermoelectromotive force value generated by the induction heating element after being heated and calculates the temperature value accordingly;

[0042] The induction heating element comprises a thermocouple having different metallic materials, wherein at least one metallic material is an electromagnetic receptor.

[0043] The cold end of the induction heating element is connected in parallel with a cold end compensation resistor R Cu , the cold end compensation resistor R Cu The resistance value is set to the corresponding resistance value R0 when the temperature is 0℃ to compensate for the cold end temperature.

[0044] Cold junction compensation resistor R Cu is a copper resistor.

[0045] The cold junction compensation resistor R Cu The measurement method of the corresponding resistance R0 at a temperature of 0°C is as follows:

[0046] The present invention is directed to the cold end compensation resistor R Cu An experimental scheme is proposed to determine the resistance value R0 corresponding to the resistance value at a temperature of 0°C. The hot end of the induction heating element 11 is placed in a constant temperature heating furnace 9, and the induction heating element 11 is wrapped with insulation cotton 10, so that the hot end of the induction heating element 11 is in a stable temperature field. The cold end of the induction heating element 11 is led out with a copper wire using the intermediate conductor law. The cold end of the induction heating element 11 is placed in a test tube 16 in an oil bath 12, and the contact is in contact with the bottom of the test tube 16. The mouth of the test tube is plugged with a cotton ball to reduce heat dissipation. The measuring device is equivalent to the resistance R 测 13, which is connected in parallel with the adjustable resistance sliding rheostat 15, the resistor R 测 13 is connected in series with the ammeter 14 and then connected to the copper wire. After the test starts, the temperature of the hot end is controlled to 350 degrees Celsius, the temperature of the cold end is controlled to 40 degrees Celsius, and the resistance value of the sliding rheostat 15 is adjusted to make the measuring device (resistance R 测 ) is 350℃±1℃, that is, ΔI≈ΔI1; use a resistance box to measure the resistance value of the sliding rheostat 15, that is, R 40 Then, the temperature of the oil bath 12 is controlled to 50°C, and the resistance value of the sliding rheostat 15 is adjusted so that the measuring device (resistance R 测 ) is 350℃±1℃, that is, ΔI≈ΔI1; use the resistance box to measure the resistance value of the sliding rheostat, that is, R 50 Generally, within a certain temperature range (such as 0-50°C), the metal resistance changes with temperature in a linear manner: R t =R0(1+ αt); then: R 40 =R0(1+40α), R 50 =R0(1+50α), where α is the temperature coefficient of resistivity, R t is the resistance value at t degree. 40 With R 50 , the two equations can be combined to obtain R0 and α, and the metal resistor material selected for cold end compensation can be determined by α; the 0℃ resistance of the compensation resistor can be determined by R0. If a copper thermal resistor is selected as the cold end compensation resistor, the metal copper resistance changes linearly with temperature in the range of 0 to 100℃, and its resistivity temperature coefficient α=4.28899×10 -3 (℃ -1 ), then use R40 =R0(1+40α) or R 50 = R0(1+50α) to determine R0.

[0047] like Figure 3 , Figure 4 As shown in the figure, the pulse width modulation (PWM) principle used in the present invention is used. The pulse width modulation refers to a method of using the on and off of semiconductor switching devices to convert the DC voltage into a voltage pulse sequence while keeping the DC voltage obtained by rectification unchanged, and changing the equivalent output voltage by controlling the period or width of the voltage pulse. The basic waveform of the PWM output voltage is as follows: Figure 3 As shown in b), Figure 3 b) and Figure 3 a) The traditional sine wave has the same heating amount. In half a cycle, the total width of the output pulse can determine the size of the average output voltage, and the effective value of the output voltage can be changed to achieve the purpose of controlling the average power of the heating element. The temperature can be accurately controlled by simply keeping the number of pulses in half a cycle unchanged and changing the width of the pulse; the temperature is measured during the period when the PWM waveform voltage V=0, and the temperature measurement time is controlled to be completed within 100 milliseconds. The period when V≠0 is the heating period. During the period when the PWM waveform voltage V=0, the controller 9 records the thermoelectric potential value of the induction heating element to obtain the surface temperature of the induction heating element.

[0048] It is understood that the present invention is described by some embodiments, and those skilled in the art are aware that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application belong to the scope of protection of the present invention.

Claims

1. A method for measuring temperature of an induction heating element, characterized in that: The following steps are involved: A. The modulation module modulates the output voltage of the power supply into a PWM waveform voltage through pulse width modulation and applies it to the induction coil. When the PWM waveform voltage V≠0, the induction coil heats the induction heating element, and the thermoelectromotive force signal generated by the induction heating element after being heated is transmitted to the controller; B. The modulation module also transmits the PWM waveform voltage signal to the controller; C. During the period when the PWM waveform voltage V=0, the controller records the thermoelectromotive force value generated by the induction heating element after being heated and calculates the temperature value accordingly; The induction heating element comprises a thermocouple having different metallic materials, wherein at least one metallic material is an electromagnetic receptor.

2. The temperature measurement method of the induction heating element according to claim 1, characterized in that: The cold end of the induction heating element is connected in parallel with a cold end compensation resistor R Cu , the cold end compensation resistor R Cu The resistance value is set to the corresponding resistance value R0 when the temperature is 0℃ to compensate for the cold end temperature.

3. The temperature measurement method according to claim 1, characterized in that: The different metal materials are selected from constantan alloy or iron-nickel alloy.

4. The temperature measurement method according to claim 2, characterized in that: The cold junction compensation resistor R Cu The resistance of pure metal material.

5. The temperature measurement method according to claim 2, characterized in that: The cold junction compensation resistor R Cu The measurement method of the corresponding resistance R0 at a temperature of 0°C is as follows: Z1. The hot end of the temperature-sensitive heating element is placed in a constant temperature heating furnace (9), the cold end is led out with a copper wire, and the cold end is placed in an oil bath (12); Z2. The measuring device is connected in series with the ammeter (14), and then connected in parallel with the sliding rheostat (15), and both ends of the parallel circuit are connected to the cold end of the temperature-sensing heating element; Z3 control the temperature of the constant temperature heating furnace (9), adjust the cold end temperature in the range of 0-50 ℃, and measure the resistance of the sliding rheostat (15) with a resistance box R t , according to the linear characteristic of resistance changing with temperature R t =R0(1+αt), α and R0 are calculated, where α is the temperature coefficient of resistivity.

6. The temperature measurement method according to claim 5, characterized in that: The cold junction compensation resistor R Cu is a copper resistor.

7. The temperature measurement method according to claim 5, characterized in that: The temperature inside the constant temperature heating furnace (9) is 300-400°C.

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