Terminal temperature measuring circuit, temperature measuring method and metering instrument

Abstract

This invention discloses a terminal temperature measurement circuit, a temperature measurement method, and a measuring instrument. The terminal temperature measurement circuit includes an NTC resistor circuit, a standard resistor RT8, a channel switching circuit, a common voltage divider circuit, a main control MCU, and a power supply circuit. The channel switching circuit is connected to the NTC resistor circuit, the standard resistor RT8, the common voltage divider circuit, the power supply circuit, and the main control MCU. The standard resistor RT8 is connected to the power supply circuit. The NTC resistor circuit includes multiple NTC thermistors, each of which is connected to both the power supply circuit and the channel switching circuit. The common voltage divider circuit forms a voltage divider loop with the resistor connected to the NTC resistor circuit or the standard resistor RT8 and the power supply circuit. The voltage divider output is connected to the analog input I / O port of the main control MCU. This invention solves the technical problems of existing terminal temperature measurement circuits, such as limited temperature measurement range, excessive AD port usage, errors introduced by power fluctuations and component deviations, and low sampling efficiency due to multi-channel switching.

Description

Technical Field

[0001] This invention relates to the field of terminal temperature monitoring technology, and in particular to a terminal temperature measuring circuit, a temperature measuring method, and a measuring instrument. Background Technology

[0002] During the field operation of electricity meters, a common fault is the melting or burning of terminals. The root cause is loose or missing terminal screws, leading to poor contact between the cable and the terminal, increased contact resistance, and severe overheating when high current flows. To address this, the State Grid and China Southern Power Grid have added terminal temperature measurement requirements to the technical specifications of various electricity meter models.

[0003] Currently, the following technical solutions are mainly used for temperature measurement of electricity meter terminals: Solution 1: Dedicated integrated circuit combined with NPN transistor solution; Invention patent with announcement number CN113778151A discloses a method, device, equipment and electricity meter for controlling the temperature of electricity meter terminals. This solution sets a PN junction temperature sensor for the terminal and uses the voltage drop of the PN junction temperature sensor to obtain the ambient temperature to achieve terminal temperature measurement; however, this solution is limited by the operating temperature range of the transistor PN junction, and the temperature measurement range cannot exceed 150℃, resulting in a monitoring blind zone in severe overheating scenarios. Option 2: NTC thermistor combined with a dedicated MCU AD port; Patent CN113701911A discloses a circuit and method for detecting the terminal temperature of an energy meter, utilizing an NTC thermistor for voltage division sampling and acquiring the data through an internal analog-to-digital converter circuit of the microcontroller. In this option, each NTC thermistor requires an independent voltage divider circuit and occupies a dedicated temperature measurement AD port on the MCU. When monitoring multiple terminal temperatures, this consumes a large amount of I / O port resources, hindering functional expansion. Furthermore, resistance deviations in the voltage divider resistors within each independent voltage divider circuit, as well as voltage deviations and fluctuations in the power supply, introduce system errors, affecting temperature measurement accuracy. The aforementioned existing technology also suffers from low sampling efficiency; after switching temperature measurement channels, a relatively long waiting time is usually required for the signal to stabilize, reducing the polling efficiency of multi-channel temperature measurements.

[0004] Therefore, in order to solve the above-mentioned technical problems, it is urgent to propose a terminal temperature measurement circuit, a temperature measurement method, and a measuring instrument. Summary of the Invention

[0005] The main objective of this invention is to propose a terminal temperature measurement circuit, a temperature measurement method, and a measuring instrument, aiming to solve the technical problems of existing terminal temperature measurement circuits, such as limited temperature measurement range, excessive occupation of MCU AD port resources, system errors introduced by power fluctuations and component deviations, and low efficiency of multi-channel switching sampling.

[0006] To achieve the above objectives, the present invention provides a terminal temperature measurement circuit, wherein the terminal temperature measurement circuit includes: an NTC resistor circuit, a standard resistor RT8, a channel switching circuit, a common voltage divider circuit, a main control MCU, and a power supply circuit;

[0007] The channel switching circuit is connected to the NTC resistor circuit, the standard resistor RT8, the common voltage divider circuit, the power supply circuit, and the main control MCU, respectively; the other end of the standard resistor RT8 is connected to the power supply circuit.

[0008] The NTC resistor circuit includes multiple NTC thermistors, with one end of each NTC thermistor connected to the power supply circuit and the other end connected to the channel switching circuit.

[0009] The common voltage divider circuit forms a voltage divider loop with the resistor connected to the NTC resistor circuit or the standard resistor RT8 and the power supply circuit, and connects the voltage divider output terminal to the analog input IO port of the main control MCU.

[0010] In one preferred embodiment, the common voltage divider circuit includes an upper voltage divider resistor R1, a lower voltage divider resistor R2, and a filter capacitor C3; one end of the upper voltage divider resistor R1 is connected to the analog output terminal of the channel switching circuit, and the other end of the upper voltage divider resistor R1 is connected to the lower voltage divider resistor R2, the filter capacitor C3, and the analog input IO port of the main control MCU, respectively; the other ends of the lower voltage divider resistor R2 and the filter capacitor C3 are grounded.

[0011] In one preferred embodiment, the channel switching circuit includes an analog switch U1, resistors R3, R4, R5, R6, R7, R8, and R9, and capacitors C1 and C2.

[0012] The channel control pins A, B, and C of the analog switch U1 are connected to resistors R4, R5, and R6, respectively. The other end of resistor R4 is connected to resistor R7 and the main control MCU's I / O port NTC_A, the other end of resistor R5 is connected to resistor R8 and the main control MCU's I / O port NTC_B, and the other end of resistor R6 is connected to resistor R9 and the main control MCU's I / O port NTC_C. The other ends of resistors R4, R5, and R6 are connected to the power supply circuit.

[0013] The power supply pins of the analog switch U1 are connected to capacitor C2 and resistor R3 respectively. The other end of resistor R3 is connected to capacitor C1 and the power supply circuit respectively. The other ends of capacitor C1 and capacitor C2 are grounded.

[0014] The enable pin and ground pin of the analog switch U1 are connected to the power supply ground.

[0015] The analog input terminal of the analog switch U1 is connected to the NTC resistor circuit and the standard resistor RT8, respectively.

[0016] The analog output terminal X of the analog switch U1 is connected to a common voltage divider circuit.

[0017] One preferred embodiment is that the NTC resistor circuit is equipped with 7 NTC thermistors.

[0018] In one preferred embodiment, the standard resistor RT8 is a high-precision fixed resistor, and the resistance deviation of the standard resistor RT8 is less than the resistance deviation of the branch where each NTC thermistor is located.

[0019] A terminal temperature measurement method using the aforementioned terminal temperature measurement circuit includes the following steps:

[0020] S1. Main control MCU power-on initialization;

[0021] S2. The control channel switching circuit connects the standard resistor to the common voltage divider circuit. After a preset delay, the output voltage of the common voltage divider circuit is sampled multiple times to obtain the average value of the reference AD ​​data.

[0022] S3. The control channel switching circuit connects the first NTC thermistor to the common voltage divider circuit. After a preset delay, the output voltage of the common voltage divider circuit is sampled multiple times to obtain the first average AD data. The current resistance value of the first NTC thermistor is calculated based on the reference average AD data and the first average AD data, and the first temperature value is obtained based on the RT resistance table.

[0023] S4. Sequentially control the channel switching circuit to connect each subsequent NTC thermistor to the common voltage divider circuit. After each channel is delayed for a preset time, multiple samples are taken to obtain the corresponding AD data average value. Calculate the current resistance value of each NTC thermistor and obtain the corresponding temperature value according to the RT resistance value table.

[0024] S5. Return to step S3 and repeat the next round of temperature measurement.

[0025] In one preferred embodiment, the current resistance value of the first NTC thermistor in step S3 is:

[0026]

[0027] in, This is the current resistance value of the first NTC thermistor. This is the resistance value of a standard resistor. The resistance value of the upper voltage divider resistor R1 is... Let R2 be the resistance value of the lower voltage divider resistor. To reference the average value of AD data, This is the average value of the first AD data corresponding to the first NTC thermistor.

[0028] In one preferred embodiment, in steps S3-S4, after each NTC thermistor sampling and AD data average value calculation is completed, the channel switching circuit is immediately controlled to switch to the next channel, so that the signal stabilization time of the next channel overlaps with the data processing time of the current channel.

[0029] In one preferred embodiment, in steps S3-S4, after calculating the resistance value of the current NTC thermistor, the corresponding temperature value is obtained by looking up the table or by interpolation based on the pre-stored RT resistance value table.

[0030] A metering instrument, the metering instrument including the aforementioned terminal temperature measuring circuit.

[0031] In the above technical solution of the present invention, the terminal temperature measurement circuit includes: an NTC resistor circuit, a standard resistor RT8, a channel switching circuit, a common voltage divider circuit, a main control MCU, and a power supply circuit; the channel switching circuit is connected to the NTC resistor circuit, the standard resistor RT8, the common voltage divider circuit, the power supply circuit, and the main control MCU respectively; the other end of the standard resistor RT8 is connected to the power supply circuit; the NTC resistor circuit includes multiple NTC thermistors, one end of each NTC thermistor is connected to the power supply circuit, and the other end is connected to the channel switching circuit; the common voltage divider circuit forms a voltage divider loop with the resistor connected to the NTC resistor circuit or the standard resistor RT8 and the power supply circuit, and connects the voltage divider output terminal to the analog input IO port of the main control MCU. The present invention solves the technical problems of existing terminal temperature measurement circuits, such as limited temperature measurement range, excessive occupation of MCU AD port resources, system errors introduced by power fluctuations and component deviations, and low sampling efficiency due to multi-channel switching.

[0032] In this invention, multiple NTC thermistors and standard resistors share a common voltage divider circuit through a channel switching circuit and are connected to the same AD port of the main control MCU. Only one AD port is needed to complete multi-channel temperature monitoring, which reduces the limitation on MCU selection and facilitates functional expansion.

[0033] In this invention, by connecting the standard resistor and each NTC thermistor to the same common voltage divider circuit, and using the measured AD value of the standard resistor as a reference for proportional calculation, the measurement error caused by power supply voltage deviation and fluctuation, as well as the resistance value deviation of each voltage divider resistor in the traditional independent voltage divider scheme, is eliminated, thereby improving the temperature measurement accuracy and reducing the number of components.

[0034] In this invention, the strategy of immediately switching to the next channel after sampling and delaying for a preset time arranges the channel switching stabilization time and the sampling period in parallel, eliminating the need to wait for the signal to stabilize before the next sampling, thus improving the efficiency of temperature measurement polling. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of a terminal temperature measuring circuit according to an embodiment of the present invention;

[0037] Figure 2 This is a schematic diagram of an NTC resistor circuit according to an embodiment of the present invention;

[0038] Figure 3 This is a schematic diagram of the standard resistor RT8 in an embodiment of the present invention;

[0039] Figure 4 This is a schematic diagram of the channel switching circuit according to an embodiment of the present invention;

[0040] Figure 5 This is a schematic diagram of a terminal temperature measurement method according to an embodiment of the present invention.

[0041] The realization of the objective, functional characteristics and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0042] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] It should be noted that all directional indicators (such as up, down, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicator will also change accordingly.

[0044] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature.

[0045] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0046] See Figures 1-4 According to one aspect of the present invention, the present invention provides a terminal temperature measurement circuit, wherein the terminal temperature measurement circuit includes: an NTC resistor circuit, a standard resistor RT8, a channel switching circuit, a common voltage divider circuit, a main control MCU, and a power supply circuit;

[0047] The channel switching circuit is connected to the NTC resistor circuit, the standard resistor RT8, the common voltage divider circuit, the power supply circuit, and the main control MCU, respectively; the other end of the standard resistor RT8 is connected to the power supply circuit.

[0048] The NTC resistor circuit includes multiple NTC thermistors, with one end of each NTC thermistor connected to the power supply circuit and the other end connected to the channel switching circuit.

[0049] The common voltage divider circuit forms a voltage divider loop with the resistor connected to the NTC resistor circuit or the standard resistor RT8 and the power supply circuit, and connects the voltage divider output terminal to the analog input IO port of the main control MCU.

[0050] Specifically, in this embodiment, the power supply circuit outputs power supply V3P3 to power its connected circuits.

[0051] Specifically, in this embodiment, the common voltage divider circuit includes an upper voltage divider resistor R1, a lower voltage divider resistor R2, and a filter capacitor C3; one end of the upper voltage divider resistor R1 is connected to the analog output terminal of the channel switching circuit, and the other end of the upper voltage divider resistor R1 is connected to the lower voltage divider resistor R2, the filter capacitor C3, and the analog input IO port of the main control MCU, respectively, and the other end of the lower voltage divider resistor R2 and the filter capacitor C3 is grounded.

[0052] Specifically, in this embodiment, the channel switching circuit includes an analog switch U1, resistors R3, R4, R5, R6, R7, R8, R9, capacitor C1, and capacitor C2.

[0053] The channel control pins A, B, and C of the analog switch U1 are connected to resistors R4, R5, and R6, respectively. The other end of resistor R4 is connected to resistor R7 and the main control MCU's I / O port NTC_A, the other end of resistor R5 is connected to resistor R8 and the main control MCU's I / O port NTC_B, and the other end of resistor R6 is connected to resistor R9 and the main control MCU's I / O port NTC_C. The other ends of resistors R4, R5, and R6 are connected to the power supply circuit.

[0054] The power supply pins of the analog switch U1 are connected to capacitor C2 and resistor R3 respectively. The other end of resistor R3 is connected to capacitor C1 and the power supply circuit respectively. The other ends of capacitor C1 and capacitor C2 are grounded.

[0055] The enable pin and ground pin of the analog switch U1 are connected to the power supply ground.

[0056] The analog input terminal of the analog switch U1 is connected to the NTC resistor circuit and the standard resistor RT8, respectively.

[0057] The analog output terminal X of the analog switch U1 is connected to a common voltage divider circuit.

[0058] Specifically, in this embodiment, the NTC resistor circuit includes 7 NTC thermistors; the NTC resistor circuit includes NTC thermistors RT1, RT2, RT3, RT4, RT5, RT6, and RT7; one end of each of the NTC thermistors RT1, RT2, RT3, RT4, RT5, RT6, and RT7 is connected to the power supply circuit, and the other end of each of the NTC thermistors RT1, RT2, RT3, RT4, RT5, RT6, and RT7 is connected to the channel switching circuit.

[0059] Specifically, in this embodiment, the standard resistor RT8 is a high-precision fixed resistor, and the resistance deviation of the standard resistor RT8 is less than the resistance deviation of the branch where each NTC thermistor is located.

[0060] See Figure 5 According to another aspect of the present invention, the present invention provides a terminal temperature measurement method, wherein the terminal temperature measurement method includes the following steps:

[0061] S1. Main control MCU power-on initialization;

[0062] S2. The control channel switching circuit connects the standard resistor to the common voltage divider circuit. After a preset delay, the output voltage of the common voltage divider circuit is sampled multiple times to obtain the average value of the reference AD ​​data.

[0063] S3. The control channel switching circuit connects the first NTC thermistor to the common voltage divider circuit. After a preset delay, the output voltage of the common voltage divider circuit is sampled multiple times to obtain the first average AD data. The current resistance value of the first NTC thermistor is calculated based on the reference average AD data and the first average AD data, and the first temperature value is obtained based on the RT resistance table.

[0064] S4. Sequentially control the channel switching circuit to connect each subsequent NTC thermistor to the common voltage divider circuit. After each channel is delayed for a preset time, multiple samples are taken to obtain the corresponding AD data average value. Calculate the current resistance value of each NTC thermistor and obtain the corresponding temperature value according to the RT resistance value table.

[0065] S5. Return to step S3 and repeat the next round of temperature measurement.

[0066] Specifically, in this embodiment, the current resistance value of the first NTC thermistor in step S3 is:

[0067]

[0068] in, This is the current resistance value of the first NTC thermistor. This is the resistance value of a standard resistor. The resistance value of the upper voltage divider resistor R1 is... Let R2 be the resistance value of the lower voltage divider resistor. To reference the average value of AD data, This is the average value of the first AD data corresponding to the first NTC thermistor.

[0069] Specifically, in this embodiment, in steps S3-S4, after each NTC thermistor sampling and AD data average value calculation is completed, the channel switching circuit is immediately controlled to switch to the next channel, so that the signal stabilization time of the next channel overlaps with the data processing time of the current channel.

[0070] Specifically, in this embodiment, in steps S3-S4, after calculating the resistance value of the current NTC thermistor, the corresponding temperature value is obtained by looking up the table or by interpolation based on the pre-stored RT resistance value table.

[0071] Specifically, in this embodiment, the main control MCU is powered on and initialized; the main control MCU outputs all 1s on its digital I / O port, making the channel control terminal [C,B,A] of analog switch U1 [1,1,1], controlling the analog input terminal X7 of analog switch U1 to connect to the analog output terminal X, and the channel selection is X7-X. After a preset delay T, the next step is executed; the main control MCU samples the analog input I / O port voltage multiple times to obtain the average value of the AD data. The main control MCU outputs all 0s to the digital I / O port, making the channel control terminal [C,B,A] of analog switch U1 [0,0,0]. This connects the analog input terminal X0 of analog switch U1 to the analog output terminal X, selecting the channel X0-X. After a preset delay T, the next step is executed. The main control MCU samples the analog input I / O port voltage multiple times to obtain the average value of the AD data. According to the formula:

[0072]

[0073] Calculate the resistance value of RT1, and then obtain the current measured temperature T1 according to the RT resistance value table. The main control MCU outputs a control signal through its digital I / O port to make the channel control terminal [C,B,A] of analog switch U1 [0,0,1]. This controls the analog input terminal X1 of analog switch U1 to be connected to the analog output terminal X, and the channel selection is X1-X. After a preset delay T, the next step is executed. The main control MCU samples the analog input I / O port voltage multiple times to obtain the average value of the AD data. According to the formula:

[0074]

[0075] Calculate the resistance value of RT2, and then obtain the current measured temperature T2 according to the RT resistance value table. The main control MCU outputs a control signal through its digital I / O port, making the channel control terminal [C,B,A] of analog switch U1 [0,1,0], which connects the analog input terminal X2 of analog switch U1 to the analog output terminal X, and the channel selection is X2-X. After a preset delay T, the next step is executed. The main control MCU samples the analog input I / O port voltage multiple times to obtain the average value of the AD data. According to the formula:

[0076]

[0077] Calculate the resistance value of RT3, and then obtain the current measured temperature T3 according to the RT resistance value table. The main control MCU outputs a control signal through its digital I / O port, making the channel control terminal [C,B,A] of analog switch U1 [0,1,1], controlling the analog input terminal X3 of analog switch U1 to connect to the analog output terminal X, and the channel selection is X3-X. After a preset delay T, proceed to the next step. The main control MCU samples the analog input I / O port voltage multiple times to obtain the average value of the AD data. According to the formula:

[0078]

[0079] Calculate the resistance value of RT4, and then obtain the current measured temperature T4 according to the RT resistance value table. The main control MCU outputs a control signal through its digital I / O port, making the channel control terminal [C,B,A] of analog switch U1 [1,0,0], thus connecting the analog input terminal X4 of analog switch U1 to the analog output terminal X, with the channel selection set to X4-X. After a preset delay T, proceed to the next step. The main control MCU samples the analog input I / O port voltage multiple times to obtain the average value of the AD data. According to the formula:

[0080]

[0081] Calculate the resistance value of RT5, and then obtain the current measured temperature T5 according to the RT resistance value table. The main control MCU outputs a control signal through its digital I / O port to make the channel control terminal [C,B,A] of analog switch U1 [1,0,1]. This connects the analog input terminal X5 of analog switch U1 to the analog output terminal X, and the channel selection is X5-X. After a preset delay T, proceed to the next step. The main control MCU samples the analog input I / O port voltage multiple times to obtain the average value of the AD data. According to the formula:

[0082]

[0083] Calculate the resistance value of RT6, and then obtain the current measured temperature T6 according to the RT resistance value table. The main control MCU outputs a control signal through its digital I / O port to make the channel control terminal [C,B,A] of analog switch U1 [1,1,0]. This connects the analog input terminal X6 of analog switch U1 to the analog output terminal X, and the channel selection is X6-X. After a preset delay T, the next step is executed. The main control MCU samples the analog input I / O port voltage multiple times to obtain the average value of the AD data. According to the formula:

[0084]

[0085] Calculate the resistance value of RT7, and then obtain the current measured temperature T7 according to the RT resistance value table. The digital I / O port of the main control MCU outputs a control signal to make the channel control terminal [C,B,A] of the analog switch U1 [1,1,1]. Control the analog input terminal X7 of the analog switch U1 to connect to the analog output terminal X, and select the channel as X7-X. After a preset delay T, return to the above steps.

[0086] According to another aspect of the present invention, a metering instrument is provided, which includes the aforementioned terminal temperature measurement circuit. The metering instrument enables a standard MCU with an AD port to perform terminal temperature measurement, requiring only one AD port to complete multi-channel temperature monitoring. It incorporates a standard resistor and a common voltage divider circuit, along with MCU program control, to sequentially connect the standard resistor and multiple NTC thermistors to the common voltage divider circuit. The voltage divider value is then connected to the MCU's AD port for analog-to-digital conversion, eliminating power supply voltage deviations and fluctuations, as well as system errors caused by resistance value deviations during individual voltage division for each temperature measurement channel. This improves temperature measurement accuracy and reduces the number of components. Furthermore, by using multiple samplings to improve sampling accuracy and employing a strategy of immediately switching to the next channel after sampling and delaying for a preset time, it eliminates the need to wait for signal stabilization before the next sampling, thus improving sampling efficiency.

[0087] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A terminal temperature measuring circuit, characterized in that, include: NTC resistor circuit, standard resistor RT8, channel switching circuit, common voltage divider circuit, main control MCU and power supply circuit; The channel switching circuit is connected to the NTC resistor circuit, the standard resistor RT8, the common voltage divider circuit, the power supply circuit, and the main control MCU, respectively; the other end of the standard resistor RT8 is connected to the power supply circuit. The NTC resistor circuit includes multiple NTC thermistors, with one end of each NTC thermistor connected to the power supply circuit and the other end connected to the channel switching circuit. The common voltage divider circuit forms a voltage divider loop between the NTC resistor circuit or the standard resistor RT8 connected to the power supply circuit, and connects the voltage divider output terminal to the analog input IO port of the main control MCU; the common voltage divider circuit includes an upper voltage divider resistor R1, a lower voltage divider resistor R2, and a filter capacitor C3; one end of the upper voltage divider resistor R1 is connected to the analog output terminal of the channel switching circuit, and the other end of the upper voltage divider resistor R1 is connected to the lower voltage divider resistor R2, the filter capacitor C3, and the analog input IO port of the main control MCU, respectively, and the other end of the lower voltage divider resistor R2 and the filter capacitor C3 is grounded.

2. The terminal temperature measuring circuit according to claim 1, characterized in that, The channel switching circuit includes an analog switch U1, resistors R3, R4, R5, R6, R7, R8, R9, capacitor C1, and capacitor C2. The channel control pins A, B, and C of the analog switch U1 are connected to resistors R4, R5, and R6, respectively. The other end of resistor R4 is connected to resistor R7 and the main control MCU's I / O port NTC_A, the other end of resistor R5 is connected to resistor R8 and the main control MCU's I / O port NTC_B, and the other end of resistor R6 is connected to resistor R9 and the main control MCU's I / O port NTC_C. The other ends of resistors R4, R5, and R6 are connected to the power supply circuit. The power supply pins of the analog switch U1 are connected to capacitor C2 and resistor R3 respectively. The other end of resistor R3 is connected to capacitor C1 and the power supply circuit respectively. The other ends of capacitor C1 and capacitor C2 are grounded. The enable pin and ground pin of the analog switch U1 are connected to the power supply ground. The analog input terminal of the analog switch U1 is connected to the NTC resistor circuit and the standard resistor RT8, respectively. The analog output terminal X of the analog switch U1 is connected to a common voltage divider circuit.

3. The terminal temperature measuring circuit according to claim 1, characterized in that, The NTC resistor circuit is equipped with 7 NTC thermistors.

4. A terminal temperature measuring circuit according to claim 1, characterized in that, The standard resistor RT8 is a high-precision fixed resistor, and the resistance deviation of the standard resistor RT8 is less than the resistance deviation of the branch where each NTC thermistor is located.

5. A terminal temperature measurement method, using the terminal temperature measurement circuit according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Main control MCU power-on initialization; S2. The control channel switching circuit connects the standard resistor to the common voltage divider circuit. After a preset delay, the output voltage of the common voltage divider circuit is sampled multiple times to obtain the average value of the reference AD ​​data. S3. The control channel switching circuit connects the first NTC thermistor to the common voltage divider circuit. After a preset delay, the output voltage of the common voltage divider circuit is sampled multiple times to obtain the first average AD data. The current resistance value of the first NTC thermistor is calculated based on the reference average AD data and the first average AD data, and the first temperature value is obtained based on the RT resistance table. S4. Sequentially control the channel switching circuit to connect each subsequent NTC thermistor to the common voltage divider circuit. After each channel is delayed for a preset time, multiple samples are taken to obtain the corresponding AD data average value. Calculate the current resistance value of each NTC thermistor and obtain the corresponding temperature value according to the RT resistance value table. S5. Return to step S2 and repeat the next round of temperature measurement.

6. The terminal temperature measurement method according to claim 5, characterized in that, The current resistance value of the first NTC thermistor in step S3 is: in, This is the current resistance value of the first NTC thermistor. This is the resistance value of a standard resistor. The resistance value of the upper voltage divider resistor R1 is... Let R2 be the resistance value of the lower voltage divider resistor. To reference the average value of AD data, This is the average value of the first AD data corresponding to the first NTC thermistor.

7. The terminal temperature measurement method according to claim 5, characterized in that, In S3-S4, after each NTC thermistor sampling and AD data average calculation is completed, the channel switching circuit is immediately controlled to switch to the next channel, so that the signal stabilization time of the next channel overlaps with the data processing time of the current channel.

8. A terminal temperature measurement method according to claim 5, characterized in that, In steps S3-S4, after calculating the resistance value of the current NTC thermistor, the corresponding temperature value is obtained by looking up the table or by interpolation based on the pre-stored RT resistance value table.

9. A measuring instrument, characterized in that, The metering instrument includes a terminal temperature measuring circuit as described in any one of claims 1-4.

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