Three-wire system thermal resistance measuring circuit

Abstract

The utility model provides a three-wire system thermal resistance measuring circuit. The three-wire system thermal resistance measuring circuit comprises a thermal resistor to be measured, an analog-to-digital converter, a first cable, a second cable and a third cable, wherein a first constant current source and a second constant current source are integrated in the analog-to-digital converter, and the equivalent resistance of the first cable, the equivalent resistance of the second cable and the equivalent resistance of the third cable are equal; the first end of the reference resistor is connected with the second end of the third cable and the first port of the reference voltage input end, and the second end of the reference resistor is connected with the second port of the reference voltage input end; two ports of the measuring voltage input end are connected with the second end of the first cable and the second end of the second cable respectively, and after the current values of the first constant current source and the second constant current source are set, the analog-to-digital converter measures the voltage value between the two ports of the voltage input end. The three-wire system thermal resistance measuring circuit disclosed by the utility model can improve the precision and reliability of thermal resistance measurement.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of electronic circuit, and particularly relates to a three-wire hot resistance measurement circuit. BACKGROUND

[0002] In the prior art, hot resistance measurement mainly has resistance voltage division and constant current source two ways, the resistance voltage division way is suitable for measuring the case of shorter line, and is not suitable for measuring the scene of longer line. The constant current source way is more suitable for measuring the scene of longer line.

[0003] The constant current source measurement way includes two-wire, three-wire, four-wire and the like. The two-wire measurement way cannot eliminate the measurement error caused by the measurement lead; the four-wire can eliminate the measurement error caused by the measurement lead, but the line is relatively complex and the price is relatively high. The three-wire can eliminate the measurement error caused by the measurement lead in the case of good lead resistance matching, but the measurement precision and reliability still need to be improved. CONTENT OF THE INVENTION

[0004] Therefore, the present disclosure provides a three-wire hot resistance measurement circuit to solve the technical problem of low measurement precision and reliability of the hot resistance measurement circuit in the prior art.

[0005] To achieve the above object, the technical scheme adopted by the present disclosure is as follows:

[0006] The three-wire hot resistance measurement circuit provided by the present disclosure includes: a to-be-measured hot resistance; an analog-digital converter internally integrated with a first constant current source and a second constant current source, the analog-digital converter including a reference voltage input end, a first constant current source output end, a second constant current source output end and a measurement voltage input end; a first cable, a first end of the first cable being connected with a first end of the to-be-measured hot resistance, and a second end of the first cable being connected with the first constant current source output end; a second cable, a first end of the second cable being connected with a second end of the to-be-measured hot resistance, and a second end of the second cable being connected with the second constant current source output end; a third cable, a first end of the third cable being connected with the second end of the to-be-measured hot resistance, and the equivalent resistances of the first cable, the second cable and the third cable being equal; a reference resistance, a first end of the reference resistance being connected with a second end of the third cable and a first port of the reference voltage input end, and a second end of the reference resistance being connected with a second port of the reference voltage input end; the first port and the second port of the measurement voltage input end being connected with the second end of the first cable and the second end of the second cable respectively, and after setting the current values of the first constant current source and the second constant current source, the analog-digital converter measures the voltage value between the first port and the second port of the measurement voltage input end.

[0007] In some embodiments, the second end of the first cable is connected to a negative electrode of the first anti-static diode, and a positive electrode of the first anti-static diode is connected to a ground terminal; and / or, the second end of the second cable is connected to a negative electrode of the second anti-static diode, and a positive electrode of the second anti-static diode is connected to the ground terminal; and / or, the second end of the third cable is connected to a negative electrode of the third anti-static diode, and a positive electrode of the third anti-static diode is connected to the ground terminal.

[0008] In some embodiments, the second end of the first cable is connected to a first end of the first filter resistor, a second end of the first filter resistor is connected to a first end of the first filter capacitor and a first port of the measurement voltage input terminal, and a second end of the first filter capacitor is connected to a ground terminal; and / or, the second end of the second cable is connected to a first end of the second filter resistor, a second end of the second filter resistor is connected to a first end of the second filter capacitor and a second port of the measurement voltage input terminal, and a second end of the second filter capacitor is connected to the ground terminal.

[0009] In some embodiments, the second end of the first cable is connected to a negative electrode of the first protection diode, a positive electrode of the first protection diode is connected to a first end of the first protection resistor, and a second end of the first protection resistor is connected to the first constant current source output terminal; and / or, the second end of the second cable is connected to a negative electrode of the second protection diode, a positive electrode of the second protection diode is connected to a first end of the second protection resistor, and a second end of the second protection resistor is connected to the second constant current source output terminal.

[0010] In some embodiments, the three-wire heating resistance measurement circuit further comprises a common mode inductor, two input ports of the common mode inductor are respectively connected to the second end of the first cable and the second end of the second cable, and two output ports of the common mode inductor are respectively connected to the first end of the first filter resistor and the first end of the second filter resistor.

[0011] In some embodiments, the three-wire heating resistance measurement circuit further comprises a first differential mode capacitor, the first differential mode capacitor is connected between the second end of the first filter resistor and the second end of the second filter resistor.

[0012] In some embodiments, a first end of the reference resistor is connected to a first end of the first common mode resistor, a second end of the first common mode resistor is connected to a first end of the first common mode capacitor and a first port of the reference voltage input terminal, and a second end of the first common mode capacitor is connected to a ground terminal; and / or, a second end of the reference resistor is connected to a first end of the second common mode resistor, a second end of the second common mode resistor is connected to a first end of the second common mode capacitor and a second port of the reference voltage input terminal, and a second end of the second common mode capacitor is connected to the ground terminal.

[0013] In some embodiments, the three-wire heating resistance measurement circuit further comprises a second differential mode capacitor, the second differential mode capacitor is connected between the second end of the first common mode resistor and the second end of the second common mode resistor.

[0014] In some embodiments, the voltage conversion units corresponding to the first constant current source output end, the second constant current source output end and the measurement voltage input end form one thermal resistance measurement channel of an analog-digital converter, and the analog-digital converter includes two thermal resistance measurement channels.

[0015] In some embodiments, the second end of the reference resistance is connected with the first end of the grounding resistance, and the second end of the grounding resistance is connected with the ground end.

[0016] Compared with the prior art, the three-wire thermal resistance measurement circuit in the embodiments of the present disclosure has the beneficial effects that: the three-wire thermal resistance measurement circuit in the embodiments of the present disclosure connects the to-be-measured thermal resistance by using three cables with the same equivalent resistance, applies the first constant current source and the second constant current source to the two ends of the to-be-measured thermal resistance respectively, collects the voltage values at the two ends of the to-be-measured thermal resistance, and measures the voltage values at the two ends of the to-be-measured thermal resistance again after exchanging the constant current sources applied to the two ends of the to-be-measured thermal resistance, so that the influence of the matching deviation between the two constant current sources on the thermal resistance measurement precision and the error caused by the thermal resistance lead can be eliminated, and the measurement precision of the thermal resistance is provided. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present disclosure, and other drawings can be obtained by those skilled in the art without creative effort.

[0018] Figure 1 is a schematic diagram of a three-wire thermal resistance measurement circuit provided by an embodiment of the present disclosure;

[0019] Figure 2 is a schematic diagram of another three-wire thermal resistance measurement circuit provided by an embodiment of the present disclosure;

[0020] Figure 3 is a schematic diagram of still another three-wire thermal resistance measurement circuit provided by an embodiment of the present disclosure. DETAILED DESCRIPTION

[0021] In order to make the technical problems to be solved by the present disclosure, the technical solutions and beneficial effects more clearly, the present disclosure will be further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present disclosure and not to limit the present disclosure.

[0022] The three-wire thermal resistance measurement circuit according to the embodiments of the present disclosure will be described in detail below in combination with the drawings.

[0023] Figure 1 is a schematic diagram of a three-wire thermal resistance measurement circuit provided by an embodiment of the present disclosure;Figure 2 is a schematic diagram of another three-wire heating resistance measurement circuit provided by an embodiment of the present disclosure; Figure 3 is a schematic diagram of still another three-wire heating resistance measurement circuit provided by an embodiment of the present disclosure. The three-wire heating resistance measurement circuit provided by an embodiment of the present disclosure will be described below in combination with Figure 1 , Figure 2 and Figure 3 .

[0024] As shown in Figure 1 , the three-wire heating resistance measurement circuit provided by an embodiment of the present disclosure includes a to-be-measured heating resistance RTD0 and an analog-digital converter internally integrated with a first constant current source IIDAC1 and a second constant current source IIDAC2. The analog-digital converter includes a reference voltage input end, a first constant current source output end, a second constant current source output end, and a measurement voltage input end. As shown in Figure 1 , the reference voltage input end includes a first port REF1+ and a second port REF1-, the first constant current source output end is connected with the first constant current source IIDAC1, the second constant current source output end is connected with the second constant current source IIDAC2, and the measurement voltage input end includes a first port AIN1 and a second port AIN2. The first port REF1+, the second port REF1-, the first port AIN1, and the second port AIN2 are all analog ports.

[0025] As shown in Figure 1 , the three-wire heating resistance measurement circuit further includes a first cable with an equivalent resistance of RL0, a second cable with an equivalent resistance of RL1, a third cable with an equivalent resistance of RL2, and a reference resistance REF. The equivalent resistances of the first cable, the second cable, and the third cable are equal in size. A first end of the first cable is connected with a first end of the to-be-measured heating resistance, and a second end of the first cable is connected with the first constant current source output end; a first end of the second cable is connected with a second end of the to-be-measured heating resistance, and a second end of the second cable is connected with the second constant current source output end; a first end of the third cable is connected with the second end of the to-be-measured heating resistance and the reference resistance, a first end of the reference resistance is connected with a second end of the third cable and the first port of the reference voltage input end, and a second end of the reference resistance is connected with the second port of the reference voltage input end; the first port and the second port of the measurement voltage input end are respectively connected with the second end of the first cable and the second end of the second cable. After the current values of the first constant current source and the second constant current source are set, the analog-digital converter measures the voltage value between the first port and the second port of the measurement voltage input end, and obtains the voltage between the V1 position of the first cable and the V2 position of the second cable, i.e., the voltage across the to-be-measured heating resistance.

[0026] The technical solution of this disclosure uses a proportional measurement method to measure the resistance value of the thermal resistor, which can achieve high-precision measurement of the thermal resistor value even without device calibration. Specifically, the analog-to-digital converter integrates two constant current sources with high accuracy and good matching. The error between the two constant current sources is small, and the dual constant current sources can be switched to the corresponding output pins of the analog-to-digital converter through software configuration. In addition, the analog-to-digital converter integrates offset self-calibration and gain self-calibration functions, which can reduce the offset error and gain error caused by the analog-to-digital converter and improve measurement accuracy.

[0027] The technical solution of this disclosure embodiment, by configuring the constant current source of the analog-to-digital converter, allows the application of the first constant current source and the second constant current source at the output terminals of the first and second constant current sources to be switched. The resistance value of the thermal resistor is measured twice before and after the switch, and the average value of the two measurements is calculated based on the resistance value of the thermal resistor to obtain the final measurement result. This can eliminate the matching error of the two constant current sources and the error of the thermal resistor lead wire, and achieve high-precision measurement of the resistance value of the thermal resistor.

[0028] Specifically, the first, second, and third cables are resistance temperature detector (RTD) leads with good conductivity and stability. The smaller the resistance difference between the three leads, the more accurate the measurement result. The fact that the three leads are made of the same material and of the same length eliminates the resistance differences between them.

[0029] To improve the reliability of the three-wire resistance thermometer circuit, the technical solution of this disclosure provides an electrostatic discharge protection scheme.

[0030] like Figure 2 As shown, the second end of the first cable is connected to the negative terminal of the first anti-static diode Z2, and the positive terminal of the first anti-static diode Z2 is connected to ground; and / or, the second end of the second cable is connected to the negative terminal of the second anti-static diode Z3, and the positive terminal of the second anti-static diode Z3 is connected to ground; and / or, the second end of the third cable is connected to the negative terminal of the third anti-static diode Z1, and the positive terminal of the third anti-static diode Z1 is connected to ground. Wherein, Z1 is an anti-static diode used for common-terminal electrostatic protection.

[0031] like Figure 2 As shown, the second end of the first cable is connected to the first end of the first filter resistor R2, the second end of the first filter resistor R2 is connected to the first end of the first filter capacitor C3 and the first port of the measurement voltage input terminal, and the second end of the first filter capacitor C3 is connected to the ground terminal; and / or, the second end of the second cable is connected to the first end of the second filter resistor R3, the second end of the second filter resistor R3 is connected to the first end of the second filter capacitor C2 and the second port of the measurement voltage input terminal, and the second end of the second filter capacitor C2 is connected to the ground terminal.

[0032] The above electrostatic protection scheme has high reliability, can perform electrostatic protection on the position contacted by personnel, prevent electrostatic damage to the core device of the three-wire heating resistance measurement circuit, and also can protect the constant current source from damage, thereby preventing damage of external static electricity to the three-wire heating resistance measurement circuit.

[0033] The first anti-static diode Z2 and the second anti-static diode Z3 provide primary electrostatic protection, and the low-pass filter circuit composed of the first filter resistor R2 and the first filter capacitor C3 and the low-pass filter circuit composed of the second filter resistor R3 and the second filter capacitor C2 can provide secondary electrostatic protection. The two-stage electrostatic protection can ensure that the internal core device of the three-wire heating resistance measurement circuit is not damaged by static electricity. Specifically, the anti-static diode can absorb most of the static electricity energy, and the secondary electrostatic protection of the low-pass filter composed of the filter resistor and the filter capacitor can prevent static electricity from damaging the internal core device of the three-wire heating resistance measurement circuit.

[0034] As shown in Figure 2 the second end of the first cable is connected to the negative electrode of the first protection diode D1, the positive electrode of the first protection diode D1 is connected to the first end of the first protection resistor R1, the second end of the first protection resistor R1 is connected to the first constant current source output end; and / or, the second end of the second cable is connected to the negative electrode of the second protection diode D2, the positive electrode of the second protection diode D2 is connected to the first end of the second protection resistor R2, and the second end of the second protection resistor R2 is connected to the second constant current source output end.

[0035] In the technical scheme of the embodiment of the present disclosure, in order to prevent the influence of large current and large voltage on the double constant current source and prevent the influence of current backflow on the measurement accuracy, a protection diode and a protection resistor can be connected in series on the constant current source output line. The protection circuit of the measurement channel in which the first constant current source output end is located is composed of the first protection diode D1 connected to the first protection resistor R1, and the protection circuit of the measurement channel in which the second constant current source output end is located is composed of the second protection diode D2 connected to the second protection resistor R2.

[0036] The three-wire heating resistance measurement circuit of the embodiment of the present disclosure uses a signal filter circuit to filter common mode noise and differential mode noise, preventing the influence of external noise on the measurement accuracy of the measurement circuit. The signal filter circuit suppresses common mode noise through a common mode inductor and an RC low-pass filter, and suppresses differential mode signals through an RC circuit.

[0037] As shown in Figure 2As shown, the three-wire heating resistance measurement circuit further comprises a common-mode inductor RA0, two input ports of the common-mode inductor RA0 are connected to the second end of the first cable and the second end of the second cable respectively, and two output ports of the common-mode inductor RA0 are connected to the first end of the first filter resistor and the first end of the second filter resistor respectively. The three-wire heating resistance measurement circuit further comprises a first differential-mode capacitor C1, which is connected between the second end of the first filter resistor and the second end of the second filter resistor.

[0038] In the above circuit, the common-mode inductor RA0 and the low-pass filter circuit composed of the first filter resistor R2 and the first filter capacitor C3 and the low-pass filter circuit composed of the second filter resistor R3 and the second filter capacitor C2 jointly act to suppress common-mode signals, and the RC circuit composed of the first differential-mode capacitor C1, the first filter resistor R2 and the second filter resistor R3 can suppress differential-mode signals. The signal filtering circuit can filter the influence of high-frequency noise on the measurement accuracy, thereby improving the measurement accuracy.

[0039] The reference resistance in the technical solution of the embodiments of the present disclosure is a high-precision resistance. By adding a filter circuit to the circuit in which the reference resistance is located, a high-precision reference voltage with noise reduction can be obtained, thereby improving the accuracy of the reference voltage and further improving the measurement accuracy.

[0040] The circuit in which the reference resistance is located forms the reference voltage of the analog-digital converter by flowing through the reference resistance through the double constant current source. The analog-digital converter integrates two constant current sources with high accuracy and good matching, selects a high-precision reference resistance, and simultaneously adds a common-mode signal suppression circuit and a differential-mode signal suppression circuit as a filter circuit, which can avoid the influence of noise on the reference voltage of the analog-digital converter, thereby ensuring that the analog-digital converter has a reference voltage with high accuracy. As shown in FIG. 2, the common-mode signal suppression circuit is composed of a first common-mode resistor R9, a first common-mode capacitor C7, a second common-mode resistor R10 and a second common-mode capacitor C8, and the differential-mode signal suppression circuit is composed of a first common-mode resistor R9, a second common-mode resistor R10 and a second differential-mode capacitor C9.

[0041] As Figure 2As shown, the first terminal of the reference resistor REF is connected to the first terminal of the first common-mode resistor R9, the second terminal of the first common-mode resistor R9 is connected to the first terminal of the first common-mode capacitor C7 and the first port of the reference voltage input terminal, and the second terminal of the first common-mode capacitor C7 is connected to ground; and / or, the second terminal of the reference resistor REF is connected to the first terminal of the second common-mode resistor R10, the second terminal of the second common-mode resistor R10 is connected to the first terminal of the second common-mode capacitor C8 and the second port of the reference voltage input terminal, and the second terminal of the second common-mode capacitor C8 is connected to ground. The three-wire heating resistor measurement circuit also includes a second differential-mode capacitor C9, which is connected between the second terminal of the first common-mode resistor R9 and the second terminal of the second common-mode resistor R10.

[0042] In this embodiment of the disclosure, the second terminal of the reference resistor REF is connected to the first terminal of the grounding resistor RG, and the second terminal of the grounding resistor RG is connected to the ground.

[0043] In this embodiment of the present disclosure, the voltage conversion units corresponding to the first constant current source output terminal, the second constant current source output terminal, and the measurement voltage input terminal constitute a resistance temperature detector (RTD) measurement channel of the analog-to-digital converter, and the analog-to-digital converter includes two RTD measurement channels.

[0044] like Figure 3 As shown, in the circuit where the first RTD measurement channel connected to the RTD under test (RTD0) is located, the measurement voltage input terminals include the first port AIN1 and the second port AIN2. In the circuit where the second RTD measurement channel connected to RTD1 is located, the measurement voltage input terminals include the first port AIN3 and the second port AIN4. The circuit where the second RTD measurement channel is located includes a third constant current source output terminal and a fourth constant current source output terminal. The third constant current source output terminal can be connected to the first constant current source IIDAC1, and the fourth constant current source output terminal can be connected to the second constant current source IIDAC2. By switching the application of the first and second constant current sources at the third and fourth constant current source output terminals, and measuring the RTD resistance twice before and after the switch, the average value of the two measurements can be calculated to obtain the final measurement result.

[0045] The loop in which the second thermal resistance measurement channel is located also includes a first anti-static diode Z4 and a second anti-static diode Z5 to prevent damage to the three-wire thermal resistance measurement circuit caused by external static electricity. The first anti-static diode Z4 and the second anti-static diode Z5 provide primary static protection, and a low-pass filter circuit composed of the first filter resistor R6 and the first filter capacitor C4 and a low-pass filter circuit composed of the second filter resistor R7 and the second filter capacitor C6 can provide secondary static protection. The second thermal resistance measurement channel uses a signal filter circuit to filter common-mode noise and differential-mode noise, thereby preventing external noise from affecting the measurement accuracy of the measurement circuit. In the signal filter circuit, the common-mode inductor RA1, the low-pass filter circuit composed of the first filter resistor R6 and the first filter capacitor C4, and the low-pass filter circuit composed of the second filter resistor R7 and the second filter capacitor C6 together can suppress common-mode signals, and the RC circuit composed of the first differential-mode capacitor C5, the first filter resistor R6, and the second filter resistor R7 can suppress differential-mode signals.

[0046] The technical solution of the embodiments of the present disclosure can eliminate the influence of matching errors between the two constant current sources and the lead impedance of the thermal resistance on the measurement accuracy of the thermal resistance value, thereby improving the measurement accuracy.

[0047] In the embodiments of the present disclosure, the algorithms for measuring the thermal resistance value by the two thermal resistance measurement channels are the same. Taking the first thermal resistance measurement as an example, the ADC (Analog-to-Digital Converter) simultaneously outputs the analog-to-digital converter pins required by the first thermal resistance measurement channel of the two constant current sources, and the two constant current sources flow through the high-precision reference resistor to form the reference voltage of the analog-to-digital converter. At the same time, the two constant current sources also flow through the thermal resistance and the lead resistance to form a voltage, which is measured by the analog-to-digital converter after passing through the static protection circuit and the filter circuit. The specific calculation formula is as follows:

[0048] The code value Code1 of the resistance value measured by the ADC for the first time can be obtained by the following formula (1):

[0049] Code1=Code ref *[IIDAC1*(RL0+RTD0)-IIDAC2*RL1] / [(IIDAC1+IIDAC2)*REF](1)

[0050] where Code ref is the full-scale code value, REF is the actual reference resistance, IIDAC1 is the excitation current generated by the first constant current source, IIDAC2 is the excitation current generated by the second constant current source, REF is the high-precision reference resistance, and RL0 and RL1 are the influence resistances.

[0051] After the exchange of constant current sources, the ADC secondly measures the voltage inputted by the measuring voltage input end to obtain the code value Code2 of the resistance value, which can be obtained by the following formula (2):

[0052] Code2=Code ref *[(IIDAC1+IIDAC2)*(RL0+RTD0)-(IIDAC1+IIDAC2)*RL2] / [2*(IIDAC1+IIDAC2)*REF] (2)

[0053] According to the code values measured twice, the average value Code is obtained by the following formula (3):

[0054] Code=(Code1+Code2) / 2=Code ref *[(IIDAC1+IIDAC2)*(RL0+RTD0)-(IIDAC1+IIDAC2)*RL2] / [2*(IIDAC1+IIDAC2)*REF] (3)

[0055] When RL0=RL1=RL2, that is, the resistances of the three leads of the thermal resistance are approximately equal, the following calculation formula (4) can be obtained:

[0056] Code=Code ref *RTD0 / 2*REF (4)

[0057] According to the code value Code ref corresponding to the reference voltage and the average value Code, the resistance value of the thermal resistance RTD0 to be measured can be obtained. It can be seen that, by using double constant current exchange measurement twice, the influence of the matching deviation between the double constant current sources on the thermal resistance measurement precision can be eliminated, because the resistances of the three leads of the thermal resistance are approximately equal, the error caused by the thermal resistance leads can also be eliminated, thereby the measurement precision of the thermal resistance can be improved.

[0058] According to the three-wire thermal resistance measurement circuit provided by the embodiment of the present disclosure, by using three cables with the same equivalent resistance to connect the thermal resistance to be measured, and by applying the first constant current source and the second constant current source to the two ends of the thermal resistance to be measured respectively, the voltage values at the two ends of the thermal resistance to be measured are collected, and after the exchange of the constant current sources applied to the two ends of the thermal resistance to be measured, the voltage values at the two ends of the thermal resistance to be measured are measured again, thereby the influence of the matching deviation between the double constant current sources on the thermal resistance measurement precision and the error caused by the thermal resistance leads can be eliminated, thereby the measurement precision of the thermal resistance is improved.

[0059] The above is only a preferred embodiment of the present disclosure, and is not used to limit the present disclosure, any modification, equivalent replacement and improvement made within the spirit and principle of the present disclosure shall be included in the protection scope of the present disclosure.

Claims

1. A three-wire heating resistance measuring circuit, characterized in that, The three-wire heating resistance measurement circuit includes: Thermistor to be measured; An analog-to-digital converter that integrates a first constant current source and a second constant current source is provided. The analog-to-digital converter includes a reference voltage input terminal, a first constant current source output terminal, a second constant current source output terminal, and a measurement voltage input terminal. A first cable, the first end of which is connected to the first end of the thermal resistor to be measured, and the second end of which is connected to the output end of the first constant current source; The second cable has a first end connected to the second end of the thermal resistor to be measured, and a second end connected to the output terminal of the second constant current source. The third cable has its first end connected to the second end of the thermal resistor to be measured, and the equivalent resistances of the first cable, the second cable, and the third cable are equal. A reference resistor, wherein the first end of the reference resistor is connected to the second end of the third cable and the first port of the reference voltage input terminal, and the second end of the reference resistor is connected to the second port of the reference voltage input terminal; The first and second ports of the voltage measurement input terminal are respectively connected to the second end of the first cable and the second end of the second cable. After setting the current values ​​of the first constant current source and the second constant current source, the analog-to-digital converter measures the voltage value between the first and second ports of the voltage measurement input terminal.

2. The three-wire heating resistance measuring circuit according to claim 1, characterized in that, The second end of the first cable is connected to the negative terminal of the first anti-static diode, and the positive terminal of the first anti-static diode is connected to ground; and / or, The second end of the second cable is connected to the negative terminal of the second anti-static diode, and the positive terminal of the second anti-static diode is connected to ground; and / or, The second end of the third cable is connected to the negative terminal of the third antistatic diode, and the positive terminal of the third antistatic diode is connected to ground.

3. The three-wire heating resistance measuring circuit according to claim 1, characterized in that, The second end of the first cable is connected to the first end of the first filter resistor, the second end of the first filter resistor is connected to the first end of the first filter capacitor and the first port of the measurement voltage input terminal, and the second end of the first filter capacitor is connected to the ground terminal. And / or, The second end of the second cable is connected to the first end of the second filter resistor, the second end of the second filter resistor is connected to the first end of the second filter capacitor and the second port of the measurement voltage input terminal, and the second end of the second filter capacitor is connected to the ground terminal.

4. The three-wire heating resistance measuring circuit according to claim 1, characterized in that, The second end of the first cable is connected to the negative terminal of the first protection diode, the positive terminal of the first protection diode is connected to the first terminal of the first protection resistor, and the second terminal of the first protection resistor is connected to the output terminal of the first constant current source; and / or, The second end of the second cable is connected to the negative terminal of the second protection diode, the positive terminal of the second protection diode is connected to the first end of the second protection resistor, and the second end of the second protection resistor is connected to the output terminal of the second constant current source.

5. The three-wire heating resistance measuring circuit according to claim 3, characterized in that, The three-wire heating resistance measurement circuit also includes a common-mode inductor. The two input ports of the common-mode inductor are respectively connected to the second end of the first cable and the second end of the second cable, and the two output ports of the common-mode inductor are respectively connected to the first end of the first filter resistor and the first end of the second filter resistor.

6. The three-wire heating resistance measuring circuit according to claim 5, characterized in that, The three-wire heating resistance measurement circuit also includes a first differential mode capacitor, which is connected between the second end of the first filter resistor and the second end of the second filter resistor.

7. The three-wire heating resistance measuring circuit according to claim 1, characterized in that, The first end of the reference resistor is connected to the first end of the first common-mode resistor, the second end of the first common-mode resistor is connected to the first end of the first common-mode capacitor and the first port of the reference voltage input terminal, and the second end of the first common-mode capacitor is connected to the ground terminal. And / or, The second end of the reference resistor is connected to the first end of the second common-mode resistor, the second end of the second common-mode resistor is connected to the first end of the second common-mode capacitor and the second port of the reference voltage input terminal, and the second end of the second common-mode capacitor is connected to the ground terminal.

8. The three-wire heating resistance measuring circuit according to claim 7, characterized in that, The three-wire heating resistance measurement circuit also includes a second differential mode capacitor, which is connected between the second end of the first common mode resistor and the second end of the second common mode resistor.

9. The three-wire heating resistance measuring circuit according to claim 1, characterized in that, The voltage conversion unit corresponding to the first constant current source output terminal, the second constant current source output terminal, and the measurement voltage input terminal constitutes a resistance temperature detector (RTD) measurement channel of the analog-to-digital converter. The analog-to-digital converter includes two RTD measurement channels.

10. The three-wire heating resistance measuring circuit according to claim 1, characterized in that, The second end of the reference resistor is connected to the first end of the grounding resistor, and the second end of the grounding resistor is connected to the ground.

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