High-precision low-cost multi-loop temperature measuring device

Abstract

The invention discloses a multi-loop temperature measuring device with high precision and low cost. Comprising a plurality of thermal resistors used for temperature measurement, a constant current source module used for providing constant current for the thermal resistors, and an analog-to-digital conversion module used for converting voltage analog quantity on the thermal resistors into voltage digital quantity in a constant current loading mode, the MCU module is used for carrying out data processing on the voltage digital quantity output by the analog-to-digital conversion module; one end of the thermal resistor is provided with a single connecting line, and the other end of the thermal resistor is provided with two connecting lines; the constant current source module is connected to the thermal resistors through a current switching electronic switch module so as to provide two paths of constant currents for the thermal resistors, and the thermal resistors are connected to the analog-to-digital conversion module through a voltage switching electronic switch module so as to sample two groups of voltage analog quantities on the thermal resistors. And the analog-to-digital conversion module is connected with the MCU module. According to the invention, the temperature measurement precision and the device cost of the multi-loop temperature measurement device are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of temperature measurement, and particularly relates to a multi-loop temperature measurement device with high precision and low cost. Background Art

[0002] A multi-loop temperature measurement device is a temperature measurement device used to achieve multi-point temperature measurement. In the prior art, a typical multi-loop temperature measurement device uses multiple thermal resistors as temperature-sensitive elements for measuring temperature. The two ends of the thermal resistor are respectively connected to a temperature measurement circuit through a single connecting wire. The temperature measurement circuit indirectly obtains the temperature of the point to be measured by measuring the resistance value of the thermal resistor, so as to achieve multi-point temperature measurement. In order to achieve the switching measurement of multi-point temperature, a multi-channel analog-to-digital conversion chip is used in its temperature measurement circuit, and its deficiencies are as follows: First, the two ends of the thermal resistor are respectively connected to the temperature measurement circuit through a single connecting wire. When the wiring length is long at the application site, affected by the wiring resistance, the temperature measurement accuracy is poor.

[0003] Second, the multi-channel analog-to-digital conversion chip used in the temperature measurement circuit is expensive, resulting in a high cost of the multi-loop temperature measurement device.

[0004] Therefore, it is necessary to improve the existing multi-loop temperature measurement device to solve the above problems. Summary of the Invention

[0005] In order to solve the above problems, the present invention proposes a multi-loop temperature measurement device with high precision and low cost, aiming to improve the temperature measurement accuracy of the multi-loop temperature measurement device and reduce the cost of the multi-loop temperature measurement device. The specific technical solutions are as follows: A multi-loop temperature measurement device with high precision and low cost includes multiple thermal resistors for temperature measurement, a constant current source module for providing a constant current for each of the thermal resistors, an analog-to-digital conversion module for converting the voltage analog quantity on the thermal resistor into a voltage digital quantity in the constant current loading mode, and an MCU module for processing the voltage digital quantity output by the analog-to-digital conversion module; the thermal resistor is a three-wire connection thermal resistor with a single connecting wire at one end and two connecting wires at the other end; the constant current source module is connected to the thermal resistor through a current switching electronic switch module to respectively provide two constant currents for each of the thermal resistors, the thermal resistor is connected to the analog-to-digital conversion module through a voltage switching electronic switch module to sample two groups of voltage analog quantities on each of the thermal resistors, and the analog-to-digital conversion module is connected to the MCU module.

[0006] In the present invention, the constant current source module includes a reference voltage chip U2 for providing a reference voltage VREF and two groups of constant current circuits for providing two constant current flows to the thermal resistor; each constant current circuit includes an operational amplifier U1A and a MOS transistor IC1. The reference voltage output terminal VREF of the reference voltage chip U2 is connected to the non-inverting input terminal of the operational amplifier U1A through a high-precision low-temperature drift resistor R1. One end of the high-precision low-temperature drift resistor R1 connected to the non-inverting input terminal of the operational amplifier U1A is also connected to the ground terminal GND through a high-precision low-temperature drift resistor R2. The inverting input terminal of the operational amplifier U1A is connected to the source S of the MOS transistor IC1. The output pin Vo of the reference voltage chip U2 is also connected to the source S of the MOS transistor IC1 through a high-precision low-temperature drift resistor R3. The output terminal of the operational amplifier U1A is connected to the gate G of the MOS transistor IC1. The drain D of the MOS transistor IC1 outputs the constant current required by the thermal resistor. The two constant current circuits respectively output two constant current flows I1 and I2 for supplying the thermal resistor.

[0007] In the present invention, the negative power supply terminal of the operational amplifier U1A is connected to the ground terminal GND, and the positive power supply terminal of the operational amplifier U1A is connected to the ground terminal GND through a filter capacitor C1.

[0008] The working principle of the constant current source module in the above multi-loop temperature measurement device is as follows: In the constant current source module, R1, R2, and R3 are high-precision low-temperature drift resistors, U1 is an operational amplifier, IC1 is a MOS transistor, C1, C2, C3, C4, and C5 are filter capacitors, and U2 is a high-precision low-temperature drift reference voltage chip.

[0009] The power supply voltage generates a high-precision reference voltage VREF through the reference voltage chip U2. VREF is divided by the resistors R1 and R2 and input to the non-inverting input terminal of the operational amplifier. After being inverted and followed, the voltage V1 is obtained. At this time, the MOS transistor is turned on, and a constant current I1 = (VREF - V1) / R3 is obtained at the load terminal connected to the drain D of the MOS transistor IC1. Two constant current flows with the same parameters form the constant current source module, which is used to generate the constant current flows I1 and I2 respectively.

[0010] In the present invention, the reference voltage chip U2 is provided with a power supply pin Vi, an output pin Vo, and a ground pin G. A filter capacitor C2 and a filter capacitor C3 are connected in parallel between the power supply line connecting the power supply pin Vi and the ground wire connecting the ground pin G. A filter capacitor C4 and a filter capacitor C5 are connected in parallel between the reference voltage output line connecting the output pin Vo and the ground wire connecting the ground pin G.

[0011] Preferably, the thermal resistor is a PT100 thermal resistor.

[0012] Preferably, the PT100 thermal resistor includes a thermal resistor PT100 with a resistance value Rpt100, a connection wire PT1-1 with a resistance value RL1 connected to one end of the thermal resistor PT100, a connection wire PT1-2 with a resistance value RL2 and a ground wire with a resistance value RL3 respectively connected to the other end of the thermal resistor PT100.

[0013] In the present invention, the current switching electronic switch module includes a current switching electronic switch chip IC2. A power input pin VCC is provided on the current switching electronic switch chip IC2, and the power input pin VCC is connected to a ground terminal GND through a filter capacitor C6; a pair of constant current input pins XOUT / YOUT and four pairs of constant current switching output pins X0 / Y0, X1 / Y1, X2 / Y2, X3 / Y3 are provided on the current switching electronic switch chip IC2. Current switching control pins A and B for realizing current output switching are further provided on the current switching electronic switch chip IC2; two paths of constant current I1 and I2 of the constant current source module are connected to a pair of constant current input pins XOUT / YOUT of the current switching electronic switch chip IC2, and the connection wire PT1-1 and the connection wire PT1-2 of the thermal resistor are correspondingly connected to a pair of constant current switching output pins X0 / Y0 of the current switching electronic switch chip IC2; the current switching control pins A and B of the current switching electronic switch chip IC2 are respectively connected to the MCU module.

[0014] The working principle of the above current switching electronic switch module is as follows: IC2 in the current switching electronic switch module is a current switching electronic switch chip, and C6 is a filter capacitor. RL1, RL2, RL3 and PT100 are PT100 thermal resistor sensors of a three-wire system. Since the error caused by the wire resistance cannot be ignored when the wiring of the thermal resistor is long during on-site installation, which will affect the temperature measurement accuracy, RL1, RL2 and RL3 are used here to simulate the wire resistance of 3 wires.

[0015] Two paths of constant current flow through the electronic switch to the PT100 thermal resistor sensor, and thus the voltages Upt1-1 = I1*(RL1 + RL3 + Rpt100) and Upt1-2 = I2*(RL2 + RL3) are obtained.

[0016] In the present invention, the voltage switching electronic switch module includes a voltage switching electronic switch chip IC3. A power input pin VCC is provided on the voltage switching electronic switch chip IC3, and the power input pin VCC is connected to the ground terminal GND through a filter capacitor C7. Four pairs of sampled voltage input pins X0 / Y0, X1 / Y1, X2 / Y2, X3 / Y3 and a pair of sampled voltage output pins XOUT / YOUT are provided on the voltage switching electronic switch chip IC3. A voltage switching control pin A and a voltage switching control pin B for realizing voltage output switching are further provided on the current switching electronic switch chip IC2. The terminal voltage Upt1-1 of the connection line PT1-1 is loaded onto one of the sampled voltage input pins X0 of a pair of sampled voltage input pins X0 / Y0, and the terminal voltage Upt1-2 of the connection line PT1-2 is loaded onto the other sampled voltage input pin Y0 of the pair of sampled voltage input pins X0 / Y0. The voltage switching control pins A and B of the voltage switching electronic switch chip IC3 are respectively connected to the analog-to-digital conversion module.

[0017] Among them, the terminal voltage Upt1-1 of the connection line PT1-1 is: Upt1-1 = I1 * (RL1 + RL3 + Rpt100); the terminal voltage Upt1-2 of the connection line PT1-2 is: Upt1-2 = I2 * (RL2 + RL3).

[0018] Among them, the resistance value Rpt100 at both ends of the thermal resistor PT100 = ΔU / I1; among them, ΔU = I1 * (RL1 + RL3 + Rpt100) - I2 * (RL2 + RL3).

[0019] The working principle of the above voltage switching electronic switch module is as follows: In the voltage switching electronic switch module, IC3 is a voltage switching electronic switch chip, and C7 is a filter capacitor. The voltage switching electronic switch chip IC3 inputs the differential voltages Upt1-1 and Upt1-2 of the previous stage into the differential voltage input port of the analog-to-digital conversion module of the subsequent stage, and obtains: ΔU = (Upt1-1) - (Upt1-2) = I1 * (RL1 + RL3 + Rpt100) - I2 * (RL2 + RL3), Since the wire resistances RL1 = RL2 = RL3 of the three wires of the three-wire PT100 thermal resistor sensor and the currents I1 = I2, it is obtained that ΔU = I1 * Rpt100, that is, the voltage value at both ends of the thermal resistor.

[0020] The MCU module obtains this voltage value by communicating with the analog-to-digital conversion module, obtains the resistance value of the thermal resistor according to the formula Rpt100 = ΔU / I1, and obtains the current temperature value through the standard temperature resistance value comparison table of the thermal resistor.

[0021] In the present invention, the MCU module controls the electronic switch module through two pins A and B to perform multi-channel switching, and samples the thermistor voltage values of each channel. Since the cost of the electronic switch is relatively low, multi-channel temperature measurement can be carried out in this way. Using multiple electronic switches to replace multi-channel analog-to-digital conversion chips or multiple analog-to-digital conversion chips can greatly reduce the cost of the device.

[0022] The present invention solves the measurement error caused by the wire resistance of the 3-wire PT100 thermistor sensor through a two-way high-precision and low-temperature-drift constant current measurement scheme, and improves the measurement accuracy of the thermistor temperature.

[0023] The beneficial effects of the present invention are as follows: First, a multi-loop temperature measurement device with high precision and low cost according to the present invention connects the PT100 thermistor to the temperature measurement circuit through three connecting wires. At the same time, a low-cost current switching electronic switch module and a voltage switching electronic switch module are used in the temperature measurement circuit to replace the conventional multi-channel analog-to-digital conversion chip. The temperature measurement channels are switched and collected through the electronic switch, thereby improving the temperature measurement accuracy of the multi-loop temperature measurement device and reducing the cost of the multi-loop temperature measurement device.

[0024] Second, a multi-loop temperature measurement device with high precision and low cost according to the present invention designs a high-precision constant current source module in the temperature measurement circuit. The high-precision reference voltage VREF is generated by the reference voltage chip U2, and after being processed by the operational amplifier U1A, a high-precision constant current required for the thermistor is generated through the MOS transistor, thereby improving the temperature measurement accuracy of the multi-loop temperature measurement device. Description of the Drawings

[0025] Figure 1 is a schematic diagram of the principle of a multi-loop temperature measurement device with high precision and low cost according to the present invention; Figure 2 is a schematic diagram of the circuit of the constant current source module; Figure 3 is a schematic diagram of the pin wiring of the current switching electronic switch chip; Figure 4 is a schematic diagram of the pin wiring of the voltage switching electronic switch chip. Detailed Embodiments

[0026] The following combines the drawings and embodiments to further describe the specific embodiments of the present invention. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and cannot be used to limit the protection scope of the present invention.

[0027] As Figures 1 to 4An embodiment of a high-precision and low-cost multi-loop temperature measurement device according to the present invention is shown, which includes a plurality of thermal resistors for temperature measurement, a constant current source module for providing a constant current for each of the thermal resistors, an analog-to-digital conversion module for converting the analog voltage on the thermal resistor into a digital voltage in the constant current loading mode, and an MCU module for processing the digital voltage output by the analog-to-digital conversion module; the thermal resistor is a three-wire connected thermal resistor with a single connecting wire at one end and two connecting wires at the other end; the constant current source module is connected to the thermal resistor through a current switching electronic switch module to provide two constant currents for each of the thermal resistors, the thermal resistor is connected to the analog-to-digital conversion module through a voltage switching electronic switch module to sample two sets of analog voltages on each of the thermal resistors, and the analog-to-digital conversion module is connected to the MCU module.

[0028] In this embodiment, the constant current source module includes a reference voltage chip U2 for providing a reference voltage VREF and two sets of constant current circuits for providing two constant currents for the thermal resistor; each constant current circuit includes an operational amplifier U1A and a MOS transistor IC1. The reference voltage output terminal VREF of the reference voltage chip U2 is connected to the non-inverting input terminal of the operational amplifier U1A through a high-precision and low-temperature-drift resistor R1. One end of the high-precision and low-temperature-drift resistor R1 connected to the non-inverting input terminal of the operational amplifier U1A is also connected to the ground terminal GND through a high-precision and low-temperature-drift resistor R2. The inverting input terminal of the operational amplifier U1A is connected to the source terminal S of the MOS transistor IC1. The output pin Vo of the reference voltage chip U2 is also connected to the source terminal S of the MOS transistor IC1 through a high-precision and low-temperature-drift resistor R3. The output terminal of the operational amplifier U1A is connected to the gate terminal G of the MOS transistor IC1. The drain terminal D of the MOS transistor IC1 outputs the constant current required for the thermal resistor. The two constant current circuits respectively output two constant currents I1 and I2 for supplying the thermal resistor.

[0029] In this embodiment, the negative power supply terminal of the operational amplifier U1A is connected to the ground terminal GND, and the positive power supply terminal of the operational amplifier U1A is connected to the ground terminal GND through a filter capacitor C1.

[0030] The working principle of the constant current source module in the above multi-loop temperature measurement device is as follows: In the constant current source module, R1, R2, and R3 are high-precision and low-temperature-drift resistors, U1 is an operational amplifier, IC1 is a MOS transistor, C1, C2, C3, C4, and C5 are filter capacitors, and U2 is a high-precision and low-temperature-drift reference voltage chip.

[0031] The supply voltage generates a high-precision reference voltage VREF through the reference voltage chip U2. VREF is input to the non-inverting input terminal of the operational amplifier after being divided by the resistors R1 and R2. After following in the reverse direction, the voltage V1 is obtained. At this time, the MOS transistor conducts, and a constant current I1 = (VREF - V1) / R3 is obtained at the load terminal connected to the drain D of the MOS transistor IC1 in Figure 2 Two constant currents with the same parameters form a constant current source module, which is used to generate constant currents I1 and I2 respectively.

[0032] In this embodiment, the reference voltage chip U2 is provided with a power supply pin Vi, an output pin Vo, and a ground pin G. A filter capacitor C2 and a filter capacitor C3 are connected in parallel between the power supply line connecting the power supply pin Vi and the ground wire connecting the ground pin G. A filter capacitor C4 and a filter capacitor C5 are connected in parallel between the reference voltage output line connecting the output pin Vo and the ground wire connecting the ground pin G.

[0033] Preferably, the thermal resistor is a PT100 thermal resistor.

[0034] Preferably, the PT100 thermal resistor includes a thermal resistor PT100 with a resistance value Rpt100, a connection wire PT1-1 with a resistance value RL1 connected to one end of the thermal resistor PT100, connection wires PT1-2 with a resistance value RL2 respectively connected to the other end of the thermal resistor PT100, and a ground wire with a resistance value RL3.

[0035] In this embodiment, the current switching electronic switch module includes a current switching electronic switch chip IC2. The current switching electronic switch chip IC2 is provided with a power input pin VCC, and the power input pin VCC is connected to the ground terminal GND through a filter capacitor C6; the current switching electronic switch chip IC2 is provided with a pair of constant current input pins XOUT / YOUT and four pairs of constant current switching output pins X0 / Y0, X1 / Y1, X2 / Y2, X3 / Y3. The current switching electronic switch chip IC2 is also provided with current switching control pins A and B for realizing current output switching; the two constant currents I1 and I2 of the constant current source module are connected to a pair of constant current input pins XOUT / YOUT of the current switching electronic switch chip IC2, and the connection wire PT1-1 and the connection wire PT1-2 of the thermal resistor are correspondingly connected to a pair of constant current switching output pins X0 / Y0 of the current switching electronic switch chip IC2; the current switching control pins A and B of the current switching electronic switch chip IC2 are respectively connected to the MCU module.

[0036] The working principle of the above current switching electronic switch module is as follows: IC2 in the current switching electronic switch module is a current switching electronic switch chip, and C6 is a filter capacitor. Figure 3 RL1, RL2, RL3, and PT100 in the left box are three-wire PT100 thermal resistance sensors. When the wiring of the thermal resistance is long during on-site installation, the error caused by the wire resistance cannot be ignored, which will affect the temperature measurement accuracy. Therefore, RL1, RL2, and RL3 are used to simulate the wire resistance of 3 wires.

[0037] Two constant currents flow through the electronic switch to the PT100 thermal resistance sensor, and thus the voltages Upt1-1 = I1 * (RL1 + RL3 + Rpt100) and Upt1-2 = I2 * (RL2 + RL3) are obtained.

[0038] In this embodiment, the voltage switching electronic switch module includes a voltage switching electronic switch chip IC3. A power input pin VCC is provided on the voltage switching electronic switch chip IC3, and the power input pin VCC is connected to the ground terminal GND through a filter capacitor C7; four pairs of sampled voltage input pins X0 / Y0, X1 / Y1, X2 / Y2, X3 / Y3 and a pair of sampled voltage output pins XOUT / YOUT are provided on the voltage switching electronic switch chip IC3. A voltage switching control pin A and B for realizing voltage output switching are also provided on the current switching electronic switch chip IC2; the terminal voltage Upt1-1 of the connection line PT1-1 is loaded onto one of the sampled voltage input pins X0 of a pair of sampled voltage input pins X0 / Y0, and the terminal voltage Upt1-2 of the connection line PT1-2 is loaded onto the other sampled voltage input pin Y0 of the pair of sampled voltage input pins X0 / Y0; the voltage switching control pins A and B of the voltage switching electronic switch chip IC3 are respectively connected to the analog-to-digital conversion module.

[0039] Among them, the terminal voltage Upt1-1 of the connection line PT1-1 is: Upt1-1 = I1 * (RL1 + RL3 + Rpt100); the terminal voltage Upt1-2 of the connection line PT1-2 is: Upt1-2 = I2 * (RL2 + RL3).

[0040] Among them, the resistance value Rpt100 at both ends of the thermal resistance PT100 = ΔU / I1; where ΔU = I1 * (RL1 + RL3 + Rpt100) - I2 * (RL2 + RL3).

[0041] The working principle of the above voltage switching electronic switch module is as follows: In the voltage switching electronic switch module, IC3 is a voltage switching electronic switch chip, and C7 is a filtering capacitor. The voltage switching electronic switch chip IC3 inputs the differential voltages Upt1-1 and Upt1-2 of the previous stage into the differential voltage input port of the analog-to-digital conversion module of the subsequent stage, and obtains: ΔU=(Upt1-1)-(Upt1-2)= I1*(RL1+RL3+Rpt100)-I2*(RL2+RL3), Since the wire resistances RL1 = RL2 = RL3 of the three wires of the three-wire PT100 thermal resistance sensor and the currents I1 = I2, it is obtained that ΔU = I1*Rpt100, which is the voltage value across the thermal resistance.

[0042] The MCU module obtains this voltage value by communicating with the analog-to-digital conversion module, obtains the resistance value of the thermal resistance according to the formula Rpt100 = ΔU / I1, and obtains the current temperature value through the standard temperature resistance value comparison table of the thermal resistance.

[0043] In this embodiment, the MCU module controls the electronic switch module to perform multi-channel switching through two pins A and B, and samples the thermal resistance voltage values of each channel. Since the cost of the electronic switch is relatively low, multi-channel temperature measurement can be performed in this way. Using multiple electronic switches to replace multi-channel analog-to-digital conversion chips or multiple analog-to-digital conversion chips can greatly reduce the cost of the device.

[0044] This embodiment adopts a two-way high-precision and low-temperature-drift constant current measurement scheme to solve the measurement error caused by the wire resistance of the three-wire PT100 thermal resistance sensor and improve the measurement accuracy of the thermal resistance temperature.

[0045] The above is only the preferred embodiment of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A high-precision, low-cost multi-circuit temperature measuring device, characterized in that: It includes a plurality of thermal resistors for temperature measurement, a constant current source module for providing a constant current to each of the thermal resistors, an analog-to-digital conversion module for converting the voltage analog quantity on the thermal resistor into a voltage digital quantity in a constant current loading mode, and an MCU module for performing data processing on the voltage digital quantity output by the analog-to-digital conversion module; The thermal resistor is a three-wire connected thermal resistor with a single connecting wire at one end and two connecting wires at the other end; the constant current source module is connected to the thermal resistor through a current switching electronic switch module to provide two constant currents for each thermal resistor respectively, and the thermal resistor is connected to the analog-to-digital conversion module through a voltage switching electronic switch module to sample and obtain two groups of voltage analog quantities on each thermal resistor, and the analog-to-digital conversion module is connected to the MCU module.

2. A high-precision, low-cost multi-circuit temperature measuring device according to claim 1, characterized in that: The constant current source module includes a reference voltage chip U2 for providing a reference voltage VREF and two groups of constant current circuits that provide two constant currents for the thermal resistor; each constant current circuit includes an operational amplifier U1A and a MOS tube IC1, the reference voltage output terminal VREF of the reference voltage chip U2 is connected to the in-phase input terminal of the operational amplifier U1A through a high-precision low-temperature drift resistor R1, one end of the high-precision low-temperature drift resistor R1 connected to the in-phase input terminal of the operational amplifier U1A is also connected to the ground terminal GND through a high-precision low-temperature drift resistor R2, the inverting input terminal of the operational amplifier U1A is connected to the source S of the MOS tube IC1, the output pin Vo of the reference voltage chip U2 is also connected to the source S of the MOS tube IC1 through a high-precision low-temperature drift resistor R3, the output terminal of the operational amplifier U1A is connected to the gate G of the MOS tube IC1, the drain D of the MOS tube IC1 outputs the constant current required by the thermal resistor, and the two constant current circuits respectively output two constant currents I1 and I2 for supplying the thermal resistor.

3. A high-precision, low-cost multi-circuit temperature measuring device according to claim 2, characterized in that: The negative power supply terminal of the operational amplifier U1A is connected to the ground terminal GND, and the positive power supply terminal of the operational amplifier U1A is connected to the ground terminal GND through the filter capacitor C1.

4. The high-precision and low-cost multi-circuit temperature measuring device according to claim 1 is characterized in that: The reference voltage chip U2 is provided with a power supply pin Vi, an output pin Vo and a ground pin G, and filter capacitors C2 and C3 are arranged in parallel between the power supply line connected to the power supply pin Vi and the ground line connected to the ground pin G, and filter capacitors C4 and C5 are arranged in parallel between the reference voltage output line connected to the output pin Vo and the ground line connected to the ground pin G.

5. A high-precision, low-cost multi-circuit temperature measuring device according to claim 2, characterized in that: The thermal resistor is a PT100 thermal resistor.

6. A high-precision, low-cost multi-circuit temperature measuring device according to claim 5, characterized in that: The PT100 thermal resistor includes a thermal resistor PT100 with a resistance value Rpt100, a connecting wire PT1-1 with a resistance value RL1 connected to one end of the thermal resistor PT100, a connecting wire PT1-2 with a resistance value RL2 respectively connected to the other end of the thermal resistor PT100, and a grounding wire with a resistance value RL3.

7. A high-precision, low-cost multi-circuit temperature measuring device according to claim 6, characterized in that: The current switching electronic switch module includes a current switching electronic switch chip IC2, and a power input pin VCC is provided on the current switching electronic switch chip IC2, and the power input pin VCC is connected to the ground terminal GND through a filter capacitor C6; a pair of constant current input pins XOUT / YOUT and four pairs of constant current switching output pins X0 / Y0, X1 / Y1, X2 / Y2, and X3 / Y3 are provided on the current switching electronic switch chip IC2, and current switching control pins A and B for realizing current output switching are also provided on the current switching electronic switch chip IC2; two constant currents I1 and I2 of the constant current source module are connected to a pair of constant current input pins XOUT / YOUT of the current switching electronic switch chip IC2, and the connecting lines PT1-1 and PT1-2 of the thermal resistor are correspondingly connected to a pair of constant current switching output pins X0 / Y0 of the current switching electronic switch chip IC2; the current switching control pins A and B of the current switching electronic switch chip IC2 are respectively connected to the MCU module.

8. The high-precision and low-cost multi-circuit temperature measuring device according to claim 6, characterized in that: The voltage switching electronic switch module includes a voltage switching electronic switch chip IC3, on which a power input pin VCC is provided, and the power input pin VCC is connected to the ground terminal GND through a filter capacitor C7; the voltage switching electronic switch chip IC3 is provided with four pairs of sampling voltage input pins X0 / Y0, X1 / Y1, X2 / Y2, X3 / Y3 and a pair of sampling voltage output pins XOUT / YOUT, and the current switching electronic switch chip IC2 is also provided with voltage switching control pins A and B for realizing voltage output switching; the terminal voltage Upt1-1 of the connecting line PT1-1 is loaded to one sampling voltage input pin X0 of the pair of sampling voltage input pins X0 / Y0, and the terminal voltage Upt1-2 of the connecting line PT1-2 is loaded to the other sampling voltage input pin Y0 of the pair of sampling voltage input pins X0 / Y0; the voltage switching control pins A and B of the voltage switching electronic switch chip IC3 are respectively connected to the analog-to-digital conversion module.

9. A high-precision, low-cost multi-circuit temperature measuring device according to claim 8, characterized in that: The terminal voltage Upt1 - 1 of the connecting line PT1 - 1 is: Upt1 - 1 = I1 * (RL1 + RL3 + Rpt100); the terminal voltage Upt1 - 2 of the connecting line PT1 - 2 is: Upt1 - 2 = I2 * (RL2 + RL3).

10. The high-precision and low-cost multi-circuit temperature measuring device according to claim 1, characterized in that: The resistance value of both ends of the thermal resistor PT100 is Rpt100=ΔU / I1; wherein, ΔU= I1*(RL1+RL3+Rpt100)-I2*(RL2+RL3).

Images