Temperature measuring device based on NTC thermistor

Abstract

The utility model discloses a temperature measuring device based on an NTC thermistor. The temperature measuring device comprises a single-chip microcomputer, a temperature measuring sensing module, a power supply VCC, a switch module, a differential amplification filtering module and an RC filtering module. The temperature measurement sensing module comprises a first resistor R1, a second resistor R2, a first capacitor C1 and an NTC thermistor Rt; the NTC thermistor Rt and the first capacitor C1 are connected in parallel, one end of the NTC thermistor Rt is grounded, the other end of the NTC thermistor Rt is connected with one end of the first resistor R1 and one end of the second resistor R2 and is connected with a voltage sampling end of the single chip microcomputer through the RC filtering module, the other end of the first resistor R1 is connected with a power supply VCC, and the other end of the second resistor R2 is connected with the power supply VCC through a controlled end of the switch module. The control end of the switch module is connected with the control output end of the single-chip microcomputer, the two input ends of the differential amplification filtering module are connected with the two ends of the second resistor R2 respectively, the output end of the differential amplification filtering module is connected with the current sampling end of the single-chip microcomputer, and the measurement precision in the wide temperature range can be guaranteed.

Description

TECHNICAL FIELD

[0001] The utility model belongs to motor temperature measurement field, concretely relates to a temperature measuring device based on NTC thermistor. BACKGROUND

[0002] The driving motor of the electric vehicle uses NTC thermistor to measure the temperature of the motor stator, and the higher the temperature of the NTC thermistor, the smaller the resistance value. When the NTC thermistor is at low temperature (for example, -20 DEG C), the resistance value changes by hundreds of ohms when the temperature increases by 1 DEG C; when the NTC thermistor is at high temperature (for example, 100 DEG C), the resistance value changes only by a few ohms when the temperature increases by 1 DEG C, which is nearly 100 times less than the change at -20 DEG C.

[0003] At present, the motor stator temperature of the electric vehicle is mainly measured by resistance voltage division method, that is, a pull-up resistor is connected in series with the NTC thermistor, a fixed voltage is applied to the two resistors, the voltage division value of the NTC thermistor and the current value flowing through the NTC thermistor are measured, the resistance value of the NTC thermistor is determined, and then the motor stator temperature is obtained by looking up the table according to the resistance value (that is, looking up the corresponding relationship table of the resistance value and the temperature of the NTC thermistor). Since the resistance value of the pull-up resistor in series is fixed, the measurement accuracy of this method can only be maintained within a small temperature range (for example, at low temperature), and in another temperature range (for example, at high temperature), the voltage and current collection are inaccurate due to the mismatch of the resistance value of the pull-up resistor, thereby reducing the measurement accuracy, and the measurement accuracy within a wide temperature range cannot be guaranteed. UTILITY MODEL CONTENTS

[0004] The utility model aims at providing a temperature measuring device based on NTC thermistor to guarantee the measurement accuracy within a wide temperature range.

[0005] The temperature measuring device based on NTC thermistor, comprising a single-chip microcomputer, a temperature measurement sensor module, a power supply VCC, a switch module, a differential amplification filter module and an RC filter module. The temperature measurement sensor module comprises a first resistor R1, a second resistor R2, a first capacitor C1 and an NTC thermistor Rt. The NTC thermistor Rt is connected in parallel with the first capacitor C1 and grounded at one end, the other end of the NTC thermistor Rt is connected with the input end of the RC filter module and one end of the first resistor R1 and one end of the second resistor R2, the output end of the RC filter module is connected with the voltage sampling end (i.e. AD_IN port) of the single-chip microcomputer, the other end of the first resistor R1 is connected with the power supply VCC, the other end of the second resistor R2 is connected with the power supply VCC through the controlled end of the switch module, the control end of the switch module is connected with the control output end (i.e. MCU_CTL port) of the single-chip microcomputer, and the two input ends of the differential amplification filter module are respectively connected with the two ends of the second resistor R2, and the output end of the differential amplification filter module is connected with the current sampling end (i.e. Cur port) of the single-chip microcomputer.

[0006] Preferably, the switch module comprises a PMOS transistor T1, an NMOS transistor T2, a third resistor R3 and a fourth resistor R4. The drain of the PMOS transistor T1 is connected to the other end of the second resistor R2, the source of the PMOS transistor T1 is connected to a power supply VCC, the gate of the PMOS transistor T1 is connected to the drain of the NMOS transistor T2 and one end of the third resistor R3, the other end of the third resistor R3 is connected to the power supply VCC, the source of the NMOS transistor T2 is connected to ground, and the gate of the NMOS transistor T2 is connected to one end of the fourth resistor R4 and a control output end of the single-chip microcomputer (i.e. MCU_CTL port), and the other end of the fourth resistor R4 is connected to ground.

[0007] Preferably, the differential amplification filter module comprises a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, an amplifier U1, a second capacitor C2 and a third capacitor C3. One end of the sixth resistor R6 is connected to one end of the second resistor R2, the other end of the sixth resistor R6 is connected to the inverting input end of the amplifier U1 and one end of the eighth resistor R8, the other end of the eighth resistor R8 is connected to the output end of the amplifier U1, one end of the seventh resistor R7 is connected to the other end of the second resistor R2, the other end of the seventh resistor R7 is connected to one end of the fifth resistor R5 and the non-inverting input end of the amplifier U1, the other end of the fifth resistor R5 is connected to ground, the power supply end of the amplifier U1 is connected to the power supply VCC and one end of the second capacitor C2, the other end of the second capacitor C2 is connected to ground, the ground end of the amplifier U1 is connected to ground, the output end of the amplifier U1 is connected to one end of the ninth resistor R9 and the current sampling end of the single-chip microcomputer (i.e. Cur port), and the other end of the third capacitor C3 is connected to ground.

[0008] Preferably, the resistance value of the fifth resistor R5 is equal to the resistance value of the eighth resistor R8, and the resistance value of the sixth resistor R6 is equal to the resistance value of the seventh resistor R7.

[0009] Preferably, the resistance value of the first resistor R1 is 200 to 400 times the resistance value of the second resistor R2.

[0010] Preferably, the RC filter module comprises a tenth resistor R10 and a fourth capacitor C4, one end of the tenth resistor R10 is connected to the other end of the NTC thermistor Rt, the other end of the tenth resistor R10 is connected to one end of the fourth capacitor C4 and the voltage sampling end of the single-chip microcomputer (i.e. AD_IN port), and the other end of the fourth capacitor C4 is connected to ground.

[0011] The working principle of the temperature measuring device is as follows:

[0012] When the control output end of the single-chip microcomputer outputs high level, the NMOS transistor T2 is turned on, the PMOS transistor T1 is turned on, the second resistor R2 is connected to the power supply VCC through the PMOS transistor T1, and the first resistor R1 and the second resistor R2 are connected in parallel to form a pull-up resistor; when the control output end of the single-chip microcomputer outputs low level, the NMOS transistor T2 is turned off, the PMOS transistor T1 is turned off, the second resistor R2 cannot be connected to the power supply VCC, and the first resistor R1 forms a pull-up resistor. Therefore, the PWM signal with different duty cycles output by the single-chip microcomputer is used to control the NMOS transistor T2, thereby controlling the on / off time of the PMOS transistor T1, adjusting the current flowing through the second resistor R2, and after being filtered by the first capacitor C1, the resistance value of the pull-up resistor is equivalent to being increased / decreased, so as to ensure the measurement accuracy in a wide temperature range.

[0013] The resistance value of the equivalent pull-up resistor connected in series with the NTC thermistor Rt can be changed, and the voltage (i.e. the voltage collected by the voltage sampling end of the single-chip microcomputer) of the NTC thermistor Rt with the resistance value changing due to temperature change is still maintained in a proper range, so that the measurement accuracy in a wide temperature range is basically maintained, and the measurement accuracy in a wide temperature range is improved, and the application range is wider. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 It is a circuit block diagram of the temperature measurement device based on the NTC thermistor in the embodiment.

[0015] Figure 2 It is a circuit schematic diagram of the temperature measurement device based on the NTC thermistor in the embodiment (the single-chip microcomputer is not shown). DETAILED DESCRIPTION

[0016] In order to enable more detailed understanding of the features and technical contents of the embodiments of the present application, the implementation of the embodiments of the present application will be described in detail below with reference to the accompanying drawings, and the accompanying drawings are only used for reference and are not used to limit the embodiments of the present application.

[0017] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terms used herein are only for the purpose of describing the embodiments of the present application and are not intended to limit the present application.

[0018] In the following description, "some embodiments" are described, which describe a subset of all possible embodiments, but it can be understood that "some embodiments" can be the same subset or different subsets of all possible embodiments, and can be combined with each other without conflict.

[0019] As Figure 1、 Figure 2 The utility model discloses a temperature measurement device based on NTC thermistor, including singlechip 1, temperature measurement sensor module 3, power supply VCC, switch module 2, differential amplification filter module 4 and RC filter module 5. Temperature measurement sensor module 3 includes first resistance R1, second resistance R2, first electric capacity C1 and NTC thermistor Rt. NTC thermistor Rt is parallel with first electric capacity C1 and one end ground, and the other end of NTC thermistor Rt connects the input of RC filter module 5 and the one end of first resistance R1, the one end of second resistance R2, and the output of RC filter module 5 connects the voltage sampling end (i.e. AD IN port) of singlechip 1, the other end of first resistance R1 connects power supply VCC, and the other end of second resistance R2 connects power supply VCC through the controlled end of switch module 2, and the control end of switch module 2 connects the control output end (i.e. MCU_CTL port) of singlechip 1, and the two input ends of differential amplification filter module 4 connect the two ends of second resistance R2 respectively, and the output end of differential amplification filter module 4 connects the current sampling end (i.e. Cur port) of singlechip 1, and the power supply end VDD of singlechip 1 connects power supply VCC, and the grounding end of singlechip 1 connects ground (not shown in the figure). As an example, the model of singlechip 1 is SAK-TC397XX-256F300S, and the voltage value U0 of power supply VCC is 5V. Figure 1

[0020] In some embodiments, the resistance value of the first resistance R1 is 200 to 400 times of the resistance value of the second resistance R2, so as to better adjust the equivalent pull-up resistance and adapt to the change of the resistance value of the NTC thermistor Rt with temperature. As an example, the resistance value of the first resistance R1 is 300 times of the resistance value of the second resistance R2, for example, R1=300K and R2=1K.

[0021] ​In some embodiments, the switch module 2 comprises a PMOS transistor T1, an NMOS transistor T2, a third resistor R3 and a fourth resistor R4. The drain and source of the PMOS transistor T1 constitute the controlled end of the switch module 2, the drain of the PMOS transistor T1 is connected to the other end of the second resistor R2, the source of the PMOS transistor T1 is connected to the power supply VCC, the gate of the PMOS transistor T1 is connected to the drain of the NMOS transistor T2 and one end of the third resistor R3, the other end of the third resistor R3 is connected to the power supply VCC, the source of the NMOS transistor T2 is connected to the ground, the gate of the NMOS transistor T2 (as the control end of the switch module 2) is connected to one end of the fourth resistor R4 and the control output end of the single-chip microcomputer 1 (i.e. the MCU_CTL port), and the other end of the fourth resistor R4 is connected to the ground. The PMOS transistor T1, the NMOS transistor T2 and the third resistor R3 are used in cooperation to realize the connection / disconnection of the second resistor R2 and the power supply VCC, which can avoid the error conduction / cutoff of the MOS transistor due to the excessive voltage difference between the source and the gate of the MOS transistor. As an example, the model of the PMOS transistor T1 is BSS84P, and the model of the NMOS transistor T2 is BSS138.

[0022] In some embodiments, the RC filtering module 5 comprises a tenth resistor R10 and a fourth capacitor C4, one end of the tenth resistor R10 (as the input end of the RC filtering module 5) is connected to the other end of the NTC thermistor Rt, the other end of the tenth resistor R10 (as the output end of the RC filtering module 5) is connected to one end of the fourth capacitor C4 and the voltage sampling end of the single-chip microcomputer 1 (i.e. the AD_IN port), and the other end of the fourth capacitor C4 is connected to the ground. The RC filtering module 5 is used to filter out stray current.

[0023] In some embodiments, the differential amplification filtering module 4 comprises a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, an amplifier U1, a second capacitor C2 and a third capacitor C3. One end of the sixth resistor R6 (as one input end of the differential amplification filtering module 4) is connected to one end of the second resistor R2, the other end of the sixth resistor R6 is connected to the inverting input end of the amplifier U1 and one end of the eighth resistor R8, the other end of the eighth resistor R8 is connected to the output end of the amplifier U1, one end of the seventh resistor R7 (as the other input end of the differential amplification filtering module 4) is connected to the other end of the second resistor R2, the other end of the seventh resistor R7 is connected to one end of the fifth resistor R5 and the non-inverting input end of the amplifier U1, the other end of the fifth resistor R5 is connected to the ground, the power supply end of the amplifier U1 is connected to the power supply VCC and one end of the second capacitor C2, the other end of the second capacitor C2 is connected to the ground, the ground end of the amplifier U1 is connected to the ground, the output end of the amplifier U1 is connected to one end of the ninth resistor R9, the other end of the ninth resistor R9 (as the output end of the differential amplification filtering module 4) is connected to one end of the third capacitor C3 and the current sampling end (i.e. the Cur port) of the single-chip microcomputer 1, the other end of the third capacitor C3 is connected to the ground. The fifth resistor R5, the sixth resistor R6, the seventh resistor R7, the eighth resistor R8 and the amplifier U1 constitute a differential operational amplifier for amplifying the current passing through the second resistor R2, the ninth resistor R9 and the third capacitor C3 constitute a filtering circuit for filtering out the stray current, and the current sampled by the current sampling end of the single-chip microcomputer 1 is the amplified equivalent direct current I.

[0024] In some embodiments, the resistance value of the fifth resistor R5 is equal to the resistance value of the eighth resistor R8, and the resistance value of the sixth resistor R6 is equal to the resistance value of the seventh resistor R7. Then the amplification factor A of the differential operational amplifier is R8 / R6. As an example, the model of the amplifier U1 adopted is MCP6001, and the resistance value of the eighth resistor R8 is 10 times the resistance value of the seventh resistor R6, so the amplification factor A of the differential operational amplifier here is 10.

[0025] The working principle of the temperature measuring device is as follows:

[0026] When the control output end of the single-chip microcomputer 1 outputs a high level, the NMOS transistor T2 is turned on, the gate voltage of the PMOS transistor T1 is pulled low, the PMOS transistor T1 is turned on, the second resistor R2 is connected to the power supply VCC through the PMOS transistor T1, and the first resistor R1 and the second resistor R2 are connected in parallel to form a pull-up resistor. When the control output end of the single-chip microcomputer 1 outputs a low level, the NMOS transistor T2 is turned off, the gate voltage of the PMOS transistor T1 is pulled high to 5V, the PMOS transistor T1 is turned off, and the second resistor R2 cannot be connected to the power supply VCC, so that the first resistor R1 forms a pull-up resistor. Therefore, the PWM signal with different duty cycles output by the single-chip microcomputer 1 can be used to control the NMOS transistor T2, and then the on / off time of the PMOS transistor T1 is controlled, the current flowing through the second resistor R2 is adjusted, and after being filtered by the first capacitor C1, the resistance value of the pull-up resistor is equivalent to being increased / decreased (equivalent to controlling the resistance value of the pull-up resistor to change between the resistance value of the first resistor R1 and the resistance value of the first resistor R1 and the second resistor R2 connected in parallel).

[0027] When the temperature change makes the voltage of the NTC thermistor Rt (i.e. the voltage U collected by the voltage sampling end of the single-chip microcomputer 1) greater than the preset upper limit voltage, the single-chip microcomputer 1 reduces the duty cycle of the PWM signal output from the control output end, which is equivalent to increasing the resistance value of the pull-up resistor. When the temperature change makes the voltage of the NTC thermistor Rt (i.e. the voltage U collected by the voltage sampling end of the single-chip microcomputer 1) less than the preset lower limit voltage, the single-chip microcomputer 1 increases the duty cycle of the PWM signal output from the control output end, which is equivalent to reducing the resistance value of the pull-up resistor. Thus, the voltage of the NTC thermistor Rt is kept between the preset lower limit voltage and the preset upper limit voltage, and the measurement accuracy in a wide temperature range is basically kept consistent. Among them, the single-chip microcomputer has multiple ways to reduce / increase the duty cycle of the PWM signal output from the control output end according to the voltage of the NTC thermistor Rt collected by the voltage sampling end, all of which belong to the prior art. Here is an implementation, for example: set the initial output duty cycle of the PWM signal of the single-chip microcomputer 1 to 50%; when the temperature change makes the voltage of the NTC thermistor Rt greater than the preset upper limit voltage, the single-chip microcomputer 1 reduces the output duty cycle of the PWM signal according to the preset gradient (for example, -10%) until the voltage of the NTC thermistor Rt is less than or equal to the preset upper limit voltage; when the temperature change makes the voltage of the NTC thermistor Rt less than the preset lower limit voltage, the single-chip microcomputer 1 increases the output duty cycle of the PWM signal according to the preset gradient (for example, 10%) until the voltage of the NTC thermistor Rt is greater than or equal to the preset lower limit voltage. As an example, the preset lower limit voltage is 2V, and the preset upper limit voltage is 3V.

[0028] According to the specific circuit structure of the temperature measuring device, it can be concluded that the resistance of the NTC thermistor Rt is: Rt=(R1*U) / (U0-U+R1*I*R6 / R8). After knowing the resistance of the NTC thermistor Rt, the temperature of the current measured object (such as a motor stator) can be obtained by looking up the table according to the resistance. The resistance calculation and table lookup process belong to the prior art.

Claims

1. A temperature measuring device based on an NTC thermistor, comprising a microcontroller (1), a temperature sensing module (3), and a power supply VCC, characterized in that: It also includes a switch module (2), a differential amplifier filter module (4), and an RC filter module (5); the temperature sensing module (3) includes a first resistor R1, a second resistor R2, a first capacitor C1, and an NTC thermistor Rt; the NTC thermistor Rt is connected in parallel with the first capacitor C1 and one end is grounded, the other end of the NTC thermistor Rt is connected to the input terminal of the RC filter module (5) and one end of the first resistor R1 and the second resistor R2, the output terminal of the RC filter module (5) is connected to the voltage sampling terminal of the microcontroller (1), the other end of the first resistor R1 is connected to the power supply VCC, the other end of the second resistor R2 is connected to the power supply VCC through the controlled terminal of the switch module (2), the control terminal of the switch module (2) is connected to the control output terminal of the microcontroller (1), the two input terminals of the differential amplifier filter module (4) are respectively connected to the two ends of the second resistor R2, and the output terminal is connected to the current sampling terminal of the microcontroller (1).

2. The temperature measuring device based on an NTC thermistor according to claim 1, characterized in that: The switching module (2) includes a PMOS transistor T1, an NMOS transistor T2, a third resistor R3 and a fourth resistor R4. The drain of the PMOS transistor T1 is connected to the other end of the second resistor R2, and the source is connected to the power supply VCC. The gate of the PMOS transistor T1 is connected to the drain of the NMOS transistor T2 and one end of the third resistor R3. The other end of the third resistor R3 is connected to the power supply VCC. The source of the NMOS transistor T2 is grounded. The gate of the NMOS transistor T2 is connected to one end of the fourth resistor R4 and the control output terminal of the microcontroller (1). The other end of the fourth resistor R4 is grounded.

3. The temperature measuring device based on an NTC thermistor according to claim 1, characterized in that: The differential amplifier and filter module (4) includes a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, an amplifier U1, a second capacitor C2, and a third capacitor C3; one end of the sixth resistor R6 is connected to one end of the second resistor R2, the other end of the sixth resistor R6 is connected to the inverting input terminal of the amplifier U1 and one end of the eighth resistor R8, the other end of the eighth resistor R8 is connected to the output terminal of the amplifier U1, one end of the seventh resistor R7 is connected to the other end of the second resistor R2, the other end of the seventh resistor R7 is connected to one end of the fifth resistor R5 and the non-inverting input terminal of the amplifier U1, the other end of the fifth resistor R5 is grounded, the power supply terminal of the amplifier U1 is connected to the power supply VCC and one end of the second capacitor C2, the other end of the second capacitor C2 is grounded, the ground terminal of the amplifier U1 is grounded, the output terminal is connected to one end of the ninth resistor R9, the other end of the ninth resistor R9 is connected to one end of the third capacitor C3 and the current sampling terminal of the microcontroller (1), and the other end of the third capacitor C3 is grounded.

4. The temperature measuring device based on an NTC thermistor according to claim 3, characterized in that: The resistance value of the fifth resistor R5 is equal to the resistance value of the eighth resistor R8, and the resistance value of the sixth resistor R6 is equal to the resistance value of the seventh resistor R7.

5. The temperature measuring device based on an NTC thermistor according to any one of claims 1 to 4, characterized in that: The resistance of the first resistor R1 is 200 to 400 times that of the second resistor R2.

6. The temperature measuring device based on an NTC thermistor according to claim 5, characterized in that: The RC filter module (5) includes a tenth resistor R10 and a fourth capacitor C4. One end of the tenth resistor R10 is connected to the other end of the NTC thermistor Rt, and the other end of the tenth resistor R10 is connected to one end of the fourth capacitor C4 and the voltage sampling terminal of the microcontroller (1). The other end of the fourth capacitor C4 is grounded.

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