Modeling method of thermistor simulation model

Abstract

The invention provides a modeling method of a thermistor simulation model, which comprises the following steps of: establishing a three-parameter model of a thermistor and an anemograph PCB (Printed Circuit Board) model comprising the model, importing the models into simulation software, inputting experimental current, and carrying out IR-drop electric simulation calculation to obtain PCB power distribution; and importing the PCB power distribution into thermal simulation software for simulation to obtain PCB temperature distribution, and completing one-time electrothermal coupling simulation. Repeatedly iterating until an iteration convergence condition is met, adding an anemograph shell, a fan and a wind tunnel model into the electric heating model, inputting an experimental wind speed, simulating to obtain electric-thermal-fluid coupling distribution of the anemograph, judging whether the core temperature of the thermistor is within a specified range, and if yes, judging whether the core temperature of the thermistor is within the specified range; and continuously correcting model parameters until an accurate thermistor simulation model is obtained. According to the method, the accurate thermistor multi-physics field coupling simulation model can be obtained, and powerful support is provided for the thermal design of PCBs including temperature sensitive elements such as thermistors.

Description

Technical Field

[0001] The present invention belongs to the field of multi-physics field simulation, and in particular relates to a modeling method of a thermistor simulation model. Background Art

[0002] Thermistors are one of the most common types of temperature sensors, widely used in modern industrial production and daily life. Thermistors are made by taking advantage of the property of ceramic semiconductor materials that their resistance changes with temperature, exhibiting different resistance values at different temperatures.

[0003] In the field of thermal simulation, modeling temperature-sensitive components such as thermistors has always been difficult. This is because the thermal simulation accuracy of such components is easily affected by the model's precision and material parameters. Component manufacturers usually do not disclose the specific internal structure and material parameters of the components, resulting in thermal simulation results that deviate far from experimental data.

[0004] Therefore, it is necessary to develop a method that can accurately fit thermistor simulation models to meet the thermal design requirements of PCBs that include temperature-sensitive components such as thermistors. This is of great significance for improving the level of multi-physics field simulation technology.

[0005] A conventional constant-temperature anemometer is designed based on the principle that the energy heated by current inside a resistor can be roughly regarded as heat removed by fluid convection. By heating a resistor with current, the resistance or voltage parameters of the component are changed by temperature, and the flowing air removes the heat to achieve a thermal equilibrium state, thereby performing temperature measurement. Summary of the Invention

[0006] The object of the present invention is to provide a modeling method for a thermistor simulation model to solve the problem that the thermal model of temperature-sensitive components such as thermistors in the prior art is not accurate enough.

[0007] The method of the present invention comprises the steps of:

[0008] 1) Establishment of the three-parameter model of thermistor and anemometer PCB model

[0009] First, by presetting the number and thickness of layers of a multilayer thermistor, the thermistor ceramic material was divided into three parts. The thermal conductivity coefficients were set as three parameters. A three-parameter model containing the thermistor was established. This model was then drawn and exported using NX12 software. A PCB model of an anemometer using this thermistor was also drawn and exported using AD20 software.

[0010] 2) Construction and solution of anemometer PCB electrothermal coupling model

[0011] Import the thermistor's three-parameter model and the anemometer PCB model into SIWAVE software; set the excitation, ambient temperature, and initial PCB temperature according to the experimental current; set the initial PCB temperature to the ambient temperature; and set the material as a temperature-dependent function. Perform IR-drop electrical simulation to obtain the PCB power distribution (PCB copper layer power density distribution diagram). This PCB power distribution is then imported into ICEPAK simulation software for board-level thermal simulation to obtain the PCB temperature distribution.

[0012] The i-th electrothermal co-simulation: The PCB temperature distribution of the i-1-th electrothermal co-simulation is imported into SIwave software, and iterative simulation is performed in the same manner as the first electrothermal co-simulation until the results of the last two electrothermal co-simulations meet the iterative convergence conditions, that is, the PCB copper layer electric loss results of the electrothermal coupling co-simulation are obtained; i ≥ 2;

[0013] 3) Construction and solution of the electric-thermal-fluid coupling model of the anemometer

[0014] Use NX12 software to draw and export the anemometer housing and wind tunnel model files, add them to ICEPAK software, and redraw the mesh along with the anemometer PCB and fan. Set the experimental wind speed to the fan speed. Set the PCB power to the PCB copper layer electrical loss result after the i-th joint simulation in step 2). Recalculate the thermal field.

[0015] 4) Determine whether the thermistor core temperature in the thermal analysis results from step 3) is within the specified range. If not, reset the thermistor parameters in ICEPAK and repeat steps 2) and 3). If so, repeat the above steps using the next set of experimental data. Input multiple sets of experimental data sequentially and continuously modify the parameters until the three parameter values that match the experimental data are obtained, ultimately obtaining the electro-thermal-fluid coupled model of the thermistor.

[0016] Furthermore, the thermistor is a multilayer chip thermistor; the structure of the thermistor is divided into an outer silver layer, a nickel layer, a tin layer, a central thermistor ceramic material and a plurality of electrode layers; the number of layers and layer thickness of the thermistor are preset values; the thermistor ceramic material is divided into three parts according to the number of layers and layer thickness: an effective heating area, an electrode end area and an electrode-free area; the three parameters are respectively the thermal conductivity coefficients of the three parts of the thermistor ceramic material.

[0017] Furthermore, the anemometer is a constant-temperature anemometer. It uses a Wheatstone bridge circuit consisting of a thermistor and three other resistors to sample wind speed. During operation, a temperature feedback circuit maintains the Wheatstone bridge in balance, ensuring the thermistor operates at a fixed temperature. The energy heated by the current inside the resistor can be roughly considered as heat removed by fluid convection. When other environmental factors, such as ambient temperature and humidity, remain unchanged, the current in the flow field changes with the flow velocity near the thermistor.

[0018] Furthermore, the three-parameter model of the thermistor is exported from NX12 software, and the file format is a step file; the 3D model of the anemometer PCB is exported from a PCB design file in a third-party EDA tool, and the file format is an ODB++ file.

[0019] Furthermore, the experimental current and experimental wind speed are test data of the anemometer in a wind tunnel, and at least five sets of data sampling are performed.

[0020] Furthermore, the conductivity in the material properties is set as a function related to temperature; the excitation conditions include an excitation current source and a voltage source; the excitation current is set to the experimental current of one set of the experimental data; and the excitation conditions are loaded on the PCB traces through SIwave software to perform IR-drop electrical simulation calculations, including: obtaining copper layer electrical loss data of each layer of the PCB to form a PCB power distribution.

[0021] Furthermore, the PCB power distribution is imported into the simulation software ICEPAK to perform PCB board-level thermal simulation, including:

[0022] Use SIWAVE to call the ICEPAK solver, set the grid parameters, the power of each component, and the electrothermal coupling convergence and iterative convergence conditions, and then perform grid drawing and temperature field analysis after the circuit board is powered on; SIWAVE software automatically starts the electrothermal coupling iterative calculation.

[0023] Furthermore, the iterative convergence condition includes:

[0024] The power difference and temperature difference of the last two electrothermal joint simulations are less than the threshold.

[0025] Furthermore, at least three joint simulations are performed, and the SIWAVE power result of the i-th simulation is set as P i , ICEPAK temperature result is T i , the convergence condition is:

[0026] |P i -P i-1 |≤0.1W and |T i -T i-1|≤0.1℃,i≥2

[0027] Furthermore, the electro-thermal-fluid coupling model includes: an anemometer PCB model, component models, an anemometer housing model, a wind tunnel model, and a fan model;

[0028] The input power of the electro-thermal-fluid coupling model includes: the electrical loss results of the PCB copper layer and the power of each component from the electro-thermal coupling joint simulation. The wind tunnel model must be sufficiently long; the fan must be oriented in the direction of the wind tunnel; the three-parameter model of the thermistor in the anemometer PCB model must extend through slot 1 on the anemometer housing model, with no gap between slot 1 and the anemometer PCB model.

[0029] The anemometer housing model is clamped in the No. 2 slot hole on the wind tunnel model, and there is no gap between the No. 2 slot hole and the anemometer housing model.

[0030] Furthermore, the experimental wind speed is set as the fan wind speed, which should be set to the experimental wind speed corresponding to the set of experimental currents.

[0031] Furthermore, the core temperature of the thermistor being within the specified range means that the absolute value of the difference from the actual operating temperature is less than a sufficiently small value.

[0032] Furthermore, the modified model parameters, i.e., the thermal conductivities of the three components of the thermistor ceramic material in the three-parameter model of the thermistor, are modified to cause the thermistor core temperature to move toward the specified range. Specifically, if the thermistor core temperature is greater than the actual operating temperature of the thermistor, the parameters are increased; otherwise, the parameters are decreased until the absolute value of the difference from the actual operating temperature falls within a specified small range.

[0033] A computer system comprises a memory, a processor and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, the steps of the method for modeling a thermistor simulation model according to any one of claims 1 to 13 are implemented.

[0034] Compared with the prior art, the advantages of the present invention are:

[0035] Based on the principle of constant temperature anemometer, a modeling method for thermistor simulation model is provided, and a thermistor three-parameter model is established.

[0036] Based on the principle that the energy heated by the current inside the resistor during the operation of the constant-temperature anemometer can be approximately regarded as the heat removed by fluid convection, multiple software programs were used to scale the thermistor, anemometer, and wind tunnel model used in the calibration experiment, and perform fluid-electric-thermal coupling simulation.

[0037] Through multiple joint simulations and iterative optimization of simulation results, the three model parameters of the thermistor are continuously corrected so that when different groups of experimental wind speeds and experimental currents are input into the thermistor model, the core temperature of the thermistor is maintained within the actual operating temperature range of the thermistor, thereby obtaining an accurate thermistor simulation model.

[0038] This invention provides a method for accurately fitting simulation models for temperature-sensitive components such as thermistors. The thermal simulation results obtained using this method have a maximum deviation of no more than 0.26%, and an average accuracy of 99.88%. This method meets the thermal design requirements of PCBs that include temperature-sensitive components such as thermistors. This method is of great significance for advancing the state of the art in multi-physics field simulation technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A flow chart of a modeling method for a thermistor simulation model according to an embodiment of the present invention;

[0040] Figure 2 A cross-sectional view of a multilayer chip thermistor according to an embodiment of the present invention;

[0041] Figure 3 A three-parameter model diagram of a thermistor shown in an embodiment of the present invention;

[0042] Figure 4 This is a PCB model of an anemometer according to an embodiment of the present invention;

[0043] Figure 5 A 3D model of an anemometer housing model shown in an embodiment of the present invention;

[0044] Figure 6 A 3D model of an electrical-thermal-fluid coupling model in ICEPAK software shown in an embodiment of the present invention;

[0045] Figure 7 The grid of the electric-thermal-fluid coupling model in the ICEPAK software shown in the embodiment of the present invention;

[0046] Figure 8 This is a diagram showing the power density distribution of the PCB copper layer in the electrothermal coupling model in the SIWAVE software according to an embodiment of the present invention (simulation condition: thermistor current is 0.18A);

[0047] Figure 9 This is a thermal distribution diagram of the copper layer caused by electrical loss in the PCB copper layer of the electrothermal coupling model in SIWAVE software shown in an embodiment of the present invention (simulation condition: thermistor current is 0.18A);

[0048] Figure 10This is a thermal distribution diagram of a three-parameter model of a thermistor in the electric-thermal-fluid coupling model in the ICEPAK software shown in an embodiment of the present invention (simulation conditions: wind speed of 4.922 m / s; thermistor current of 0.17367 A);

[0049] Figure 11 This is a thermal distribution diagram of the anemometer PCB model of the electric-thermal-fluid coupling model in the ICEPAK software shown in an embodiment of the present invention (simulation conditions: wind speed of 4.922 m / s; thermistor current of 0.17367 A);

[0050] Figure 12 This is a fluid distribution diagram of the electro-thermal-fluid coupling model in the ICEPAK software shown in an embodiment of the present invention (simulation conditions: wind speed of 4.922 m / s; thermistor current of 0.17367 A);

[0051] Figure 13 This is a thermal distribution diagram of the anemometer PCB model in the ICEPAK software before and after the electric-thermal-fluid coupling model of the copper layer electrical loss is introduced according to an embodiment of the present invention (simulation conditions: wind speed of 7.5m / s, thermistor current of 0.1802A).

[0052] Figure 14 The figure shows a real object of a constant temperature anemometer, experimental tools and experimental environment according to an embodiment of the present invention. DETAILED DESCRIPTION

[0053] The following is a more detailed description of the modeling method for thermistor simulation model of the present invention, with reference to a schematic diagram. A preferred embodiment of the present invention is shown, and it should be understood that those skilled in the art may modify the present invention described herein while still achieving the advantageous effects of the present invention. Therefore, the following description should be understood as being generally known to those skilled in the art and not intended to limit the present invention.

[0054] This embodiment provides a method for modeling a thermistor simulation model, the process is as follows Figure 1 As shown, the following steps are included:

[0055] Step 1: Establish the three-parameter model of the thermistor and the anemometer PCB model

[0056] First, by presetting the number and thickness of layers of a multilayer thermistor, the thermistor ceramic material is divided into three parts. The thermal conductivity of each part is set as a parameter, thereby establishing a three-parameter model containing the thermistor.

[0057] Use NX12 software to draw and export the three-parameter model of the thermistor; use AD20 software to draw and export the anemometer PCB model using (assembling) the thermistor, such as Figure 4 shown.

[0058] like Figure 2 The figure shows a cross-sectional view of the thermistor model in the anemometer, which is drawn by NX12 software.

[0059] The thermistor is a multi-layer chip thermistor; the structure of the thermistor is divided into an outer silver layer 1, a nickel layer 2, a tin layer 3, a central thermal ceramic material 5 and a plurality of electrode layers 4.

[0060] Specifically, the electrode layer 4 is wrapped in the thermosensitive ceramic material 5 , and both ends of the thermosensitive ceramic material 5 include a tin layer 3 , a nickel layer 2 , and a silver layer 1 arranged in sequence from the inside to the outside.

[0061] The number and thickness of the thermistor are preset values; the thermistor ceramic material is divided into three parts according to the number and thickness of the layers: an effective heating area 5b, an electrode end area 5c, and an electrode-free area 5a; the three parameters are the thermal conductivity coefficients of the three parts of the thermistor ceramic material.

[0062] The length calculation process of the thermistor core area, that is, the effective heating area, is:

[0063] The resistivity of the thermosensitive material at 25°C is preset to be 500Ω·cm, the number of layers is 10, the layer thickness is 0.0013cm, and the electrode layer thickness is 0.00016cm;

[0064] Each layer of resistance is in parallel, and there are 10 layers in total. Since the resistance of the thermistor is 22Ω at 25℃, the resistance of each layer is 22*10=220Ω;

[0065] The width of the thermistor is 0.068cm, which is also the width of the effective heating area;

[0066] The height of the effective heating area is 0.0013*10+0.00016*11=0.01476 cm; wherein 0.00016 is the distance between the electrode layer and the adjacent electrode layer in the effective heating area; wherein the effective heating area is the overlapping area of the electrode layers.

[0067] According to the resistance law R = ρL / S, the single layer area S = 0.0013 / (220 / 500) = 0.00295cm 2 , so the length of the effective heating area is S / 0.068, which is 0.434mm;

[0068] According to the size of the effective heating area, the thermal ceramic material can be divided into three parts. Figure 3 As shown, 5b is the effective heating area; the thermal conductivity coefficients of 5a, 5b, and 5c are set as three parameters.

[0069] Specifically, the specific steps of dividing the thermosensitive ceramic material into three parts are:

[0070] Find the center line of the electrode layer, and find the length boundary of the effective heating area 5b according to the length of the effective heating area 0.434mm. The area within the length boundary is the effective heating area 5b.

[0071] The other regions of all electrode layers constitute the electrode end regions 5c;

[0072] The three-parameter model of the thermistor removes the tin layer 3, nickel layer 2, silver layer 1 at both ends, the effective heating area 5b, and the area 5c at both ends of the electrode. The remaining area is the electrode-free area 5a.

[0073] The anemometer corresponding to the anemometer PCB model is a constant temperature anemometer.

[0074] The anemometer uses a Wheatstone bridge circuit consisting of a thermistor on the anemometer PCB model and three other resistors to sample wind speed.

[0075] During operation, the temperature feedback circuit keeps the Wheatstone bridge balanced to ensure that the thermistor operates at a fixed temperature. The energy heated by the current inside the resistor can be approximately regarded as the heat removed by fluid convection. When other environmental factors such as ambient temperature and humidity remain unchanged, the current in the flow field changes with the flow velocity near the thermistor.

[0076] The three-parameter model of the thermistor is exported from NX12 software in the step file format. The 3D model of the anemometer PCB model is exported from the PCB design file in a third-party EDA tool in the ODB++ file format.

[0077] Step 2: Construction and solution of anemometer PCB electrothermal coupling model

[0078] Import the anemometer PCB model into SIWAVE software and set the excitation conditions, ambient temperature, and PCB initial temperature according to the experimental current:

[0079] The excitation conditions include an excitation current source and a voltage source; the excitation current is set to the experimental current of one of the experimental data sets; the experimental data include the experimental current and the experimental wind speed corresponding to the experimental current, which is the test data of the anemometer when the actual anemometer is in the wind tunnel; at least five groups of data are sampled, that is, the number of groups of experimental data is 5.

[0080] Among them, in step 2, only one set of experimental currents in the experimental data is used, and in step 3, five sets of experimental currents and five sets of experimental wind speeds are used.

[0081] The initial PCB temperature is the ambient temperature.

[0082] In addition, the material properties also need to be set as a temperature-dependent function. Specifically, the conductivity in the material properties is set as a temperature-dependent function.

[0083] Use SIwave software to load excitation conditions on the PCB traces to perform IR-drop electrical simulation calculations, obtain the electrical loss data of the copper layer of each PCB layer, and form the PCB power distribution;

[0084] Import the PCB power distribution into the simulation software ICEPAK to perform PCB board-level thermal simulation and obtain the PCB temperature distribution:

[0085] Use SIWAVE to call the ICEPAK solver, set the grid parameters, the power of each component, and the electrothermal coupling convergence and iterative convergence conditions, and then perform grid drawing and temperature field analysis after the circuit board is powered on; SIWAVE software automatically starts the electrothermal coupling iterative calculation.

[0086] The power of each component refers to the main heating element, including the thermistor, and is calculated using a specific formula based on the current. There are eight heating elements, and the power varies with the current. The thermal distribution diagram also shows that the temperatures of the other components are lower than those of the thermistor.

[0087] The i-th electrothermal joint simulation: import the PCB temperature distribution of the i-1-th electrothermal joint simulation into SIwave software, and perform iterative simulation in the same way as the first electrothermal joint simulation until the results of the last two electrothermal joint simulations meet the iterative convergence conditions, that is, the PCB copper layer electrical loss result of the electrothermal coupling joint simulation is obtained, that is, Figure 8 ;i≥2;

[0088] The iterative convergence conditions include:

[0089] The power difference and temperature difference of the last two electrothermal joint simulations are less than the threshold.

[0090] Furthermore, at least three joint simulations are performed, and the SIWAVE power result of the i-th simulation is set as P i , ICEPAK temperature result is T i , the convergence condition is:

[0091] |P i -P i-1 |≤0.1W and |T i -T i-1 |≤0.1℃,i≥2

[0092] It can be found that: when the ambient temperature is 24.9℃, without considering the components, such as Figure 9As shown in the figure, the maximum temperature of the copper layer near the thermistor reaches 35°C. As a temperature-sensitive component, the thermistor is easily affected by the ambient temperature. The influence of the copper temperature on the accuracy of the anemometer simulation calibration cannot be ignored.

[0093] according to Figure 13 The simulation results shown in the figure compare the thermistor core temperature before and after the copper electrical loss temperature is introduced in the electric-thermal-fluid model. When the wind speed is 7.5 m / s, the thermistor current is 0.1802 A, and the thermistor is subjected to 250 iterations, the difference in the thermistor core temperature is 0.561°C. The core temperature refers to the temperature of the active area.

[0094] Step 3: Construction and solution of the electric-thermal-fluid coupling model of the anemometer

[0095] Use NX12 software to draw and export the model files of the anemometer housing model and wind tunnel model, and add them to the ICEPAK software. After assembling them with the anemometer PCB model and fan model, an electro-thermal-fluid coupling model is formed. Finally, the electro-thermal-fluid coupling model is re-drawn for meshing, as shown in the following example: Figures 6-7 As shown in the figure, the fan model is established in ICEPAK.

[0096] The input power of the electro-thermal-fluid coupling model includes: PCB power and component power. The PCB power is set to the PCB copper layer electrical loss result after the i-th joint simulation in step 2.

[0097] Set the experimental wind speed to the fan speed, corresponding to the experimental current.

[0098] Finally, recalculate the thermal field.

[0099] like Figure 5 As shown in the figure, the constant temperature anemometer model includes: an anemometer PCB model, various component models including the three-parameter model of thermistor, and an anemometer housing model;

[0100] The three-parameter model of the thermistor in the anemometer PCB model extends out of slot No. 1 on the anemometer housing model, and there is no gap between slot No. 1 and the anemometer PCB model.

[0101] like Figure 6 As shown, the electric-thermal-fluid coupling model includes: a constant temperature anemometer model, a wind tunnel model, and a fan model; one end face of the wind tunnel model is open, and the other end face is set as a fan model;

[0102] A second slot hole is provided on the inner wall of the wind tunnel model for placing the anemometer housing model, and there is no gap between the second slot hole and the anemometer housing model.

[0103] like Figure 6As shown in the figure, the arrow direction is the wind speed direction. The red area is the fan model.

[0104] like Figure 7 As shown, the number of grids is about 3.07 million.

[0105] Step 4, determining whether the core temperature of the three-parameter model of the thermistor in the thermal analysis result in step 3 is within a specified range;

[0106] If not, reset the thermosensitive parameters in ICEPAK and repeat steps 2 and 3. If yes, repeat the above steps using the next set of experimental data.

[0107] Multiple sets of experimental data are input in sequence, and the parameters are continuously modified until three parameter values that meet the experimental data are obtained, and finally the electric-thermal-fluid coupling model of the thermistor is obtained.

[0108] The thermistor core temperature is within the specified range when the absolute value of the difference from the actual operating temperature is less than a sufficiently small value.

[0109] Correcting the model parameters involves correcting the thermal conductivity of the three components of the thermistor ceramic material in the thermistor's three-parameter model. Correcting the parameters is necessary to bring the thermistor core temperature within the specified range. Specifically, if the thermistor core temperature is higher than the actual operating temperature, the parameters should be increased; otherwise, the parameters should be decreased until the absolute difference from the thermistor's actual operating temperature falls within a specified, small range.

[0110] The theoretical basis of this simulation parameter determination method:

[0111] When the anemometer is working, there are four factors that affect the temperature change of the thermistor, namely, the self-heating of the resistor caused by the current, the heat convection between the resistor and the moving fluid, the heat conduction between the resistor and the PCB, and the heat radiation between the resistor and the environment.

[0112] Since the heat conduction and heat radiation of the thermistor account for a relatively small proportion when the anemometer is working, the main considerations when using the thermistor are the heat convection and self-heating power between the resistor and the moving fluid.

[0113] When the temperature of the thermistor remains unchanged, it reaches a thermal equilibrium state. According to the thermal equilibrium theory, ignoring the heat radiation part, the heat generated by the resistor in the flow field (self-heating power) should be equal to the heat dissipated (heat convection between the resistor and the moving fluid). That is,

[0114] I 2 R=W=Q t =αS(T w -T f )

[0115] Where: W is the thermal power of the thermistor; I is the current passing through the thermistor; R is the resistance of the thermistor; Q t is the heat dissipation rate of the thermistor, that is, the heat energy carried away by the fluid; α is the convection heat transfer coefficient; S is the contact area between the thermistor and the fluid; T w is the surface temperature of the thermistor; T f is the temperature of the fluid.

[0116] The relationship between the heat transfer coefficient and the velocity and direction of the flow field flowing through the resistor can be obtained from the King formula, that is,

[0117]

[0118] Where: A, B are constants related to the structure and material parameters of the thermistor; v is the fluid velocity.

[0119] Combining the above two equations, we can get the corresponding relationship between the flow velocity of the flow field and the thermistor current under thermal equilibrium conditions, that is,

[0120]

[0121] When the actual anemometer corresponding to this PCB model is powered on, the corresponding bridge arm supplies current to the thermistor, causing it to heat up. When the temperature reaches a certain value, the bridge reaches equilibrium. When fluid removes heat from the thermistor, its temperature drops, causing its resistance to increase, unbalancing the bridge and outputting an unbalanced signal. This signal is amplified by the negative feedback circuit and fed back to the bridge's power control terminal, increasing the bridge voltage and the thermistor's current. This increased current causes the thermistor to heat up again until it reaches the desired temperature, bringing the bridge back to a new equilibrium. This temperature is the thermistor's actual operating temperature, which it maintains throughout the anemometer's operation.

[0122] The corresponding relationship between the thermistor current and wind speed can be found by the different balance points of the bridge at different wind speeds.

[0123] In the electro-thermal-fluid coupled simulation of a constant-temperature anemometer, as long as the thermistor model is sufficiently accurate and the thermistor core temperature is maintained at the actual operating temperature, the relationship between current and wind speed in the simulation can be equivalent to the actual corresponding relationship.

[0124] The thermal conductivity of the ceramic material inside a multilayer chip thermistor is usually not disclosed by the manufacturer. However, by substituting the current and wind speed data measured experimentally into the simulation and maintaining the thermistor core temperature at 88.89°C, the accurate thermal conductivity of the thermistor material can be reversely deduced, completing an accurate thermistor simulation model.

[0125] Since the relationship between current and wind speed is nonlinear, if the existence of electrodes and effective heating areas is not considered, and the thermistor ceramic material is set as a whole, and the thermal conductivity of the whole is set as the only parameter, it is difficult to fit an accurate target nonlinear function. In order to ensure that the fitted function is sufficiently accurate, as many parameters as possible should be set.

[0126] The present invention divides the thermistor ceramic material into three parts according to the number and thickness of layers of the preset multilayer chip resistor, and sets the corresponding thermal conductivity as three parameters, thereby establishing a three-parameter model including the thermistor.

[0127] The simulation diagram in this embodiment is as follows Figures 10-12 As shown. Figure 14 As shown, the experimental data used in this example was measured in the environment depicted in the figure. The wind speed sensor used for calibrating wind speed was aligned with the constant-temperature anemometer in the wind tunnel near the air outlet. To ensure uniform wind speed measurements, the wind tunnel duct was extended as much as possible, and a one-meter-long wind tunnel was used for the experiment. Even so, the sensor is quite sensitive, and the data is unstable, fluctuating within a certain range. Five wind speed settings were tested for approximately five minutes each, yielding hundreds of data points for each setting. These data were weighted averaged using Matlab software to generate five sets of experimental data.

[0128] Table 1 shows the simulation results and model parameter fitting results for the thermistor core temperature obtained from these five data sets. All temperatures are within the specified range, with the absolute difference from 88.89°C not exceeding 0.07°C. The maximum deviation in the thermal simulation results for this thermistor simulation model is no more than 0.78‰, with an average accuracy of 99.95%. The current in Table 1 refers to the current flowing through the thermistor.

[0129] Table 1 Experimental data, thermistor core temperature simulation results and model parameter fitting results

[0130]

[0131]

[0132] The above description is merely a preferred embodiment of the present invention and does not limit the present invention in any way. Any person skilled in the art who, without departing from the scope of the present invention, makes any equivalent substitution, modification, or other changes to the technical solution and technical content disclosed in the present invention shall be deemed to be within the scope of the present invention and still fall within the scope of protection of the present invention.

Claims

1. A method for modeling a thermistor simulation model, characterized in that: The following steps are involved: Step 1: Establish the three-parameter model of the thermistor and the anemometer PCB model: In the three-parameter model of thermistors, the thermal ceramic material consists of three parts, each of which corresponds to a thermal conductivity parameter. Draw and derive the three-parameter model of the thermistor. Draw and export the anemometer PCB model equipped with a three-parameter model of the thermistor; Step 2: Construction and solution of anemometer PCB electrothermal coupling model: Import the anemometer PCB model into SIWAVE software, set the excitation conditions, ambient temperature, and PCB initial temperature; the excitation conditions include an excitation current source and a voltage source; the excitation current is set to the experimental current of one set in the experimental data; the experimental data includes the experimental current and the experimental wind speed corresponding to the experimental current; Then, IR-drop electrical simulation calculation is performed to obtain the power density distribution diagram of the PCB copper layer; Importing the PCB power distribution into the simulation software ICEPAK to perform PCB board-level thermal simulation to obtain the PCB temperature distribution; When the result of the electrothermal co-simulation meets the iterative convergence condition, the electrical loss result of the PCB copper layer of the electrothermal coupling co-simulation is obtained; Step 3: Construction and solution of the electric-thermal-fluid coupling model of the anemometer: Draw and export the model files of the anemometer housing model and wind tunnel model, add them to the ICEPAK software, and assemble them with the anemometer PCB model and fan model to form an electro-thermal-fluid coupling model. Finally, redraw the mesh of the electro-thermal-fluid coupling model. Set the experimental wind speed to the fan speed; set the PCB power to the PCB copper layer power loss result in step 2; Recalculate the thermal field and output the thermal analysis results; Step 4: Determine whether the thermistor core temperature in the thermal analysis results from step 3 is within the specified range; if not, reset the thermistor parameters in ICEPAK and repeat steps 2 and 3; Multiple sets of experimental data are input in sequence, and the parameters are continuously modified until the three thermal conductivity parameter values that meet the experimental data are obtained, and finally the electric-thermal-fluid coupling model of the anemometer is obtained.

2. The modeling method of the thermistor simulation model according to claim 1, wherein The three-parameter model of the thermistor includes: The electrode layer (4) is wrapped in a thermosensitive ceramic material (5), and both ends of the thermosensitive ceramic material (5) include a tin layer (3), a nickel layer (2), and a silver layer (1) arranged in sequence from the inside to the outside; The thermosensitive ceramic material (5) comprises an effective heating area (5b), areas at both ends of the electrode (5c) and an electrode-free area (5a); the effective heating area (5b) is an overlapping area of the electrode layer.

3. The modeling method of the thermistor simulation model according to claim 2, wherein The length of the effective heating area is calculated, and then the thermosensitive ceramic material (5) is divided into three parts according to the length of the effective heating area.

4. The modeling method of the thermistor simulation model according to claim 1, wherein The experimental current and experimental wind speed are test data of the anemometer in a wind tunnel, and at least five sets of data are sampled.

5. The modeling method of the thermistor simulation model according to claim 1, wherein The iterative convergence condition in step 2 is: the power difference between the last two electric-thermal joint simulations is less than a threshold and the temperature difference is less than a threshold.

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