Automatic detection circuit and method for three-wire heating resistance wire sequence

Abstract

The embodiment of the present disclosure relates to an automatic detection circuit and method for a three-wire heating resistance wire sequence. The three wires of the three-wire heating resistance to be detected can be connected to the 1 port, the 2 port and the 3 port of the terminal in any sequence, without the need to pay attention to the electrical definition, thereby improving the convenience of assembly and effectively saving the installation and debugging time; the first constant current source is connected to the fixed port, and the second constant current source is selectively connected to the 2 port and the 3 port of the terminal through the first switch and the second switch; the use of two equal constant current sources (i.e. the first constant current source and the second constant current source) as excitation to convert the resistance value of the heating resistance to be detected into a voltage signal has extremely high anti-interference ability; whether the heating resistance to be detected is correctly connected to the measurement loop is judged according to the differential pressure signal, and if not, it can be corrected through a switch switching; and the measurement error introduced by the lead resistance can be eliminated.

Description

Technical Field

[0001] This disclosure relates to the fields of industrial control, detection, and instrumentation control technology, and in particular to an automatic detection circuit and method for the wire sequence of a three-wire resistance thermometer. Background Technology

[0002] In industrial control and testing fields, resistance temperature detectors (RTDs) and thermocouples are the most widely used temperature measurement sensors. RTDs, in particular, are widely used in industrial control and experimental research with high temperature control requirements due to their high measurement accuracy, good linearity, and high reliability. RTDs sense temperature based on the resistance effect, with lead resistance being the main source of error. Currently, three-wire and four-wire RTDs have been developed. Because they are simpler than four-wire systems and their measurement accuracy meets most application requirements, three-wire systems are more widely used in scientific research and industrial settings. For three-wire RTDs, common measurement methods include the Wheatstone bridge method and the dual current source excitation method. Due to the strong anti-interference capability of current, the use of a constant current source to excite the RTD and generate a voltage signal is widely applied. The dual constant current source excitation method can effectively eliminate the error caused by lead resistance. It uses two identical constant current sources: one flows through the RTD and ground to form a loop, and the other flows through a compensating wire and ground to form a loop. The voltage difference across the RTD eliminates the lead resistance error. The voltage difference signal is then amplified and filtered, and transmitted as voltage and current.

[0003] However, while the application of the three-wire system solves the error problem, it also introduces complex wiring issues. Installation must be carried out strictly in accordance with the electrical definition. If the wiring sequence is incorrect, that is, if the two current sources are injected from the two wires with compensation terminals respectively, the voltages generated by the two constant current sources on the thermal resistor will cancel each other out, the differential voltage signal will be almost zero, and it will not work properly. If the electrical definition is unclear, it may be necessary to make several adjustments to install it correctly, which will affect the efficiency of on-site installation and commissioning and the convenience of use. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides an automatic detection circuit and method for the wiring sequence of a three-wire resistance temperature detector (RTD). This addresses the problems in existing technologies where the three-wire system, while solving error issues, also introduces complex wiring. Installation requires strict adherence to electrical definitions. If the wiring sequence is incorrect (i.e., the two current sources are injected from the two wires containing the compensation terminals), the voltages generated by the two constant current sources on the RTD cancel each other out, resulting in a near-zero differential voltage signal and preventing normal operation. Furthermore, if the electrical definitions are unclear, several adjustments may be required for correct installation, impacting on-site installation and debugging efficiency and ease of use.

[0005] According to a first aspect of the present disclosure, an automatic detection circuit for the wire sequence of a three-wire heating resistor is provided, comprising:

[0006] The output terminal of terminal block 1 is connected to the input terminal of the first current-limiting resistor. The output terminal of terminal block 2 is connected to the input terminal of the first switch. The output terminal of terminal block 3 is connected to the input terminal of the second switch. The output terminals of the first current-limiting resistor and the first constant current source are both connected to the positive input terminal of the differential operational amplifier. The normally closed terminal of the first switch and the normally open terminal of the second switch are both connected to the output terminal of the second constant current source. The normally open terminal of the first switch and the normally closed terminal of the second switch are connected in series with the second current-limiting resistor and grounded. The normally open terminal of the first switch and the normally closed terminal of the second switch are both connected to the negative input terminal of the differential operational amplifier. The output terminal of the differential operational amplifier is connected to the input terminal of the analog-to-digital converter. The output terminal of the analog-to-digital converter is connected to the microprocessor. The microprocessor is electrically connected to the switch control unit. The switch control unit is electrically connected to the first switch and the second switch respectively.

[0007] The first constant current source is used to flow through the first current-limiting resistor, port 1 of the terminal block, the thermal resistor to be measured, port 2 or 3 of the terminal block, the closed contact of the first switching switch branch, the second current-limiting resistor, and ground to form a first current loop.

[0008] The second constant current source is used to flow through port 2 of the terminal block, the thermal resistor to be measured, port 3 of the terminal block, the normally closed second switching switch, the second current limiting resistor, and ground to form a second current loop.

[0009] The first current-limiting resistor acts on the first current loop to prevent the first constant current source from short-circuiting to ground. The resistance value of the first current-limiting resistor is less than the resistance value corresponding to the lowest temperature in the ambient temperature range of the thermal resistor under test.

[0010] The second current-limiting resistor acts on the second current loop to prevent the second constant current source from short-circuiting to ground. The resistance value of the second current-limiting resistor is less than the resistance value corresponding to the lowest temperature in the ambient temperature range of the thermal resistor under test.

[0011] The first switching switch and the second switching switch are used to switch the two switches in response to the instructions of the microprocessor to change the flow direction of the second constant current source; wherein, the normally closed of the first switching switch and the normally open of the second switching switch are connected to the second constant current source, the normally open of the first switching switch and the normally closed of the second switching switch are connected in series with a second current limiting resistor to ground, and the contacts of the two switches are respectively connected to the other two ports occupied by the first constant current source.

[0012] The differential operational amplifier is used to amplify and condition the differential voltage signal across the resistor under test to the range of the analog-to-digital converter.

[0013] The microprocessor is used to acquire temperature and voltage signals and take their absolute values. It determines whether the switching switch is activated based on the voltage value. When the voltage difference is less than the set threshold, it indicates that the wiring sequence does not meet the requirements. After switching, normal measurement can be achieved.

[0014] According to a second aspect of the present disclosure, an automatic detection method for the wire sequence of a three-wire heating resistor is provided, applied to any of the above-described automatic detection circuits for the wire sequence of a three-wire heating resistor, the method comprising:

[0015] Connect the three wires of the RTD to be tested to ports 1, 2 and 3 of the terminal block respectively; wherein the first switch is normally closed and the second switch is normally open.

[0016] When the circuit is powered on, the microprocessor performs a power-on self-test. This self-test includes reading the output voltage of the differential operational amplifier and determining whether the wiring is correct based on the voltage. If the voltage is greater than a set threshold, the three wires of the RTD under test are determined to be correctly connected. If the voltage is less than the set threshold, the three wires of the RTD under test are determined not to be correctly connected to the measurement circuit. In this case, the microprocessor sends an action command to the switch control unit to correct the wiring sequence. The switch control unit controls the first switch and the second switch to switch so that the first switch is normally open and the second switch is normally closed.

[0017] The resistance of the thermal resistor to be measured can be obtained by taking the absolute value of the voltage, dividing it by the amplification factor of the differential operational amplifier, and then dividing it by the current of the first constant current source. The temperature value can be obtained through the corresponding relationship.

[0018] The switch control unit is used to control the first switching switch and the second switching switch to switch on or off.

[0019] The technical solutions provided by the embodiments of this disclosure may include the following beneficial effects:

[0020] In the embodiments of this disclosure, through the above-described automatic detection circuit and method for the three-wire resistance temperature detector (RTD) wiring sequence, the three wires of the RTD under test can be connected to ports 1, 2, and 3 of the terminal block in any wiring sequence, without needing to consider its electrical definition, thus improving assembly convenience and effectively saving installation and debugging time. The first constant current source is connected to a fixed port, and the second constant current source can be selectively connected from ports 2 and 3 of the terminal block through the first and second switching switches. Using two equal constant current sources (i.e., the first and second constant current sources) as excitation to convert the resistance value of the RTD under test into a voltage signal has extremely high anti-interference capability. The difference in voltage signal is used to determine whether the RTD under test is correctly connected to the measurement circuit. If it is incorrect, it can be corrected by switching once. Furthermore, the measurement error introduced by the lead resistance can be eliminated. Attached Figure Description

[0021] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure. It is obvious that the drawings described below are merely some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0022] Figure 1 A schematic diagram of an automatic detection circuit for the wiring sequence of a three-wire heating resistor is shown in an exemplary embodiment of the present disclosure.

[0023] Figure 2 The diagram illustrates the steps of an automatic detection method for the wire sequence of a three-wire heating resistor in an exemplary embodiment of the present disclosure.

[0024] Figure 3 This diagram illustrates a circuit schematic representing the first scenario that occurs after the PT100 is randomly connected to a terminal block in an exemplary embodiment of this disclosure.

[0025] Figure 4 A circuit diagram illustrating a second scenario that occurs after the PT100 is randomly connected to the terminal block in an exemplary embodiment of this disclosure;

[0026] Figure 5 This diagram illustrates a third scenario that occurs when the PT100 is randomly connected to a terminal block in an exemplary embodiment of this disclosure.

[0027] In the diagram, 1 is the first constant current source; 2 is the second constant current source; 3 is the first current-limiting resistor; 4 is the second current-limiting resistor; 5 is the first switching switch; 6 is the second switching switch; 7 is the switch control unit; 8 is the terminal block; 9 is the differential operational amplifier; 10 is the analog-to-digital converter; 11 is the microprocessor; and 12 is the reference point. Detailed Implementation

[0028] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, they are provided so that this disclosure will be more comprehensive and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0029] Furthermore, the accompanying drawings are merely illustrative diagrams of embodiments of this disclosure and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted. Some block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0030] This example implementation first provides an automatic detection circuit for the wire sequence of a three-wire heating resistor. (Reference) Figure 1 As shown, the automatic detection circuit for the three-wire heating resistor wire sequence may include:

[0031] The output terminal of port 1 of terminal block 8 is connected to the input terminal of the first current-limiting resistor 3. The output terminal of port 2 of terminal block 8 is connected to the input terminal of the first switching switch 5. The output terminal of port 3 of terminal block 8 is connected to the input terminal of the second switching switch 6. The output terminals of the first current-limiting resistor 3 and the first constant current source 1 are both connected to the positive input terminal of the differential operational amplifier 9. The normally closed terminal of the first switching switch 5 and the normally open terminal of the second switching switch 6 are both connected to the output terminal of the second constant current source 2. The normally open terminal of the first switching switch 5 and the normally closed terminal of the second switching switch 6 are connected in series with the second current-limiting resistor 4 and grounded. The normally open terminal of the first switching switch 5 and the normally closed terminal of the second switching switch 6 are both connected to the negative input terminal of the differential operational amplifier 9. The output terminal of the differential operational amplifier 9 is connected to the input terminal of the analog-to-digital converter 10. The output terminal of the analog-to-digital converter 10 is connected to the microprocessor 11. The microprocessor 11 is electrically connected to the switch control unit 7. The switch control unit 7 is electrically connected to the first switching switch 5 and the second switching switch 6 respectively.

[0032] Through the above-described automatic detection circuit for the three-wire RTD wiring sequence, the three wires of the three-wire RTD under test can be connected to ports 1, 2, and 3 of terminal 8 in any wiring sequence, without needing to consider its electrical definition, thus improving assembly convenience and effectively saving installation and debugging time. The first constant current source 1 is connected to a fixed port, and the second constant current source 2 can be selectively connected from ports 2 and 3 of terminal 8 through the first switching switch 5 and the second switching switch 6. Using two equal constant current sources (i.e., the first constant current source 1 and the second constant current source 2) as excitation to convert the resistance value of the RTD under test into a voltage signal has extremely high anti-interference capability. The circuit determines whether the RTD under test is correctly connected to the measurement circuit based on the differential pressure signal. If it is incorrect, it can be corrected by switching once. Furthermore, it can eliminate the measurement error introduced by the lead resistance.

[0033] Below, we will refer to Figure 1 The various parts of the automatic detection circuit for the three-wire heating resistor in this example embodiment will be described in more detail.

[0034] In one embodiment, the first constant current source 1 (i.e., constant current source 1) is used to flow through the first current limiting resistor 3 (i.e., current limiting resistor 1), port 1 of the terminal 8, the thermal resistor to be measured, port 2 or 3 of the terminal 8, the closed contact of the branch of the first switching switch 5 (i.e., switching switch 1), the second current limiting resistor 4 (i.e., current limiting resistor 2), and ground to form the first current branch (i.e., the first current loop).

[0035] The second constant current source 2 (i.e., constant current source 2) is used to flow through port 2 of terminal 8, the thermal resistor to be measured, port 3 of terminal 8, the closed contact of the branch of the second switching switch 6 (i.e., switching switch 2), the second current limiting resistor 4, and ground to form a second current loop (i.e., second current loop).

[0036] In one embodiment, the first current-limiting resistor 3 acts on the circuit of the first constant current source 1, which can prevent the first constant current source 1 from short-circuiting to ground, and at the same time improve the voltage level, thereby achieving the purpose of improving the signal-to-noise ratio. Its resistance value should be less than the resistance value corresponding to the lowest temperature in the ambient temperature range of the thermal resistor.

[0037] The second current-limiting resistor 4 acts on the circuit of the second constant current source 2, which can prevent the second constant current source 2 from short-circuiting to ground, and at the same time improve the voltage level, thereby achieving the purpose of improving the signal-to-noise ratio. Its resistance value should be less than the resistance value corresponding to the lowest temperature in the operating environment of the thermal resistor.

[0038] In one embodiment, the first switching switch 5 and the second switching switch 6 are used to switch the two switches (i.e., the first switching switch 5 and the second switching switch 6) in response to instructions from the microprocessor 11 (i.e., MCU) to change the flow direction of the second constant current source 2. They are the execution elements for adjusting the wiring sequence. The normally closed switch of the first switching switch 5 and the normally open switch of the second switching switch 6 are connected to the second constant current source 2. The normally open switch of the first switching switch 5 and the normally closed switch of the second switching switch 6 are connected in series with a current-limiting resistor to ground. The contacts of the two switches are respectively connected to the other two ports occupied by the first constant current source 1.

[0039] In one embodiment, the switch control unit 7 is used to control the switching switch to switch on or off;

[0040] Terminal 8 is used to connect a three-wire heating resistor in any wiring sequence (one wire per port);

[0041] The differential operational amplifier 9 is used to amplify and condition the differential voltage signal across the RTD to the range of the analog-to-digital converter 10.

[0042] The analog-to-digital converter 10 (ADC) has the function of measuring positive and negative voltages and is used to convert the analog voltage signal output by the differential operational amplifier 9 into a digital signal.

[0043] The microprocessor 11 is used to acquire temperature and voltage signals and take their absolute values. It determines whether the switching switch is activated based on the voltage value. When the voltage difference is less than the set threshold, it indicates that the wiring sequence does not meet the requirements. After switching, normal measurement can be achieved.

[0044] Reference point 12 is used to provide a circuit for constant current sources and active devices, and generally refers to ground.

[0045] Furthermore, this example embodiment also provides an automatic detection method for the wire sequence of a three-wire heating resistor. (See reference) Figure 2 As shown, the automatic detection method for the three-wire heating resistor wire sequence may include steps S101 to S103.

[0046] Step S101: Connect the three wires of the RTD to be tested to ports 1, 2 and 3 of terminal 8 respectively; wherein the first switch 5 is normally closed and the second switch 6 is normally open.

[0047] Step S102: Power on the circuit, and the microprocessor 11 performs a power-on self-test; wherein, the power-on self-test includes reading the output voltage of the differential operational amplifier 9, and judging whether the wiring is correct by the voltage. If the voltage is greater than a set threshold, it is determined that the three wires of the RTD under test are correctly connected. If the voltage is less than the set threshold, it is determined that the three wires of the RTD under test are not correctly connected to the measurement circuit. Then, the microprocessor 11 sends an action command to the switch control unit 7 to correct the wiring sequence. The switch control unit 7 controls the first switching switch 5 and the second switching switch 6 to switch so that the first switching switch 5 is normally open and the second switching switch 6 is normally closed.

[0048] Step S103: Take the absolute value of the voltage, divide it by the amplification factor of the differential operational amplifier 9, and then divide it by the current of the first constant current source 1 to obtain the resistance value of the thermal resistor to be measured. The temperature value is obtained through the corresponding relationship.

[0049] In one specific embodiment, an automatic detection circuit for the wire sequence of a three-wire resistance temperature detector (RTD) includes a first constant current source 1, a second constant current source 2, a first current-limiting resistor 3, a second current-limiting resistor 4, a first switching switch 5, a second switching switch 6, a switch control unit 7, a terminal block 8 (connected to the three wires of the RTD), a differential operational amplifier 9, an ADC, an MCU, and a reference point 12. The following detailed description uses a three-wire PT100 RTD as the sensor:

[0050] When the three wires of a three-wire PT100 are randomly connected to the terminal block without knowing their electrical definitions, the following issues may occur. Figure 3 , Figure 4 and Figure 5 Three scenarios.

[0051] like Figure 3 As shown, assuming the ambient temperature is >-20℃, i.e., R pt100 >92Ω, the differential operational amplifier has a gain of G times, R limit1 =R limit2 <92Ω:

[0052] Step 1: Connect the three wires of the three-wire heating resistor to the terminals respectively (assuming they are...). Figure 3 (structural access).

[0053] Step 2: The current I1 from constant current source 1 passes through current-limiting resistor 1, terminal port 1, lead resistor 1, thermal resistor, lead resistor 3, terminal port 3, the normally closed path of switch 2, and current-limiting resistor 2, flowing into the reference point and generating voltage U at the non-inverting input of the differential operational amplifier. + =I1*(R limit1 +R lead1 +R pt100 +R lead3 );

[0054] Step 3: The current I2 from constant current source 2 flows into the reference point through the normally closed path of switch 1, terminal port 2, lead resistor 2, lead resistor 3, and current limiting resistor 2, generating a voltage U at the inverting terminal of the differential operational amplifier. - =I2*(R lead2 +R lead3 +R limit2 );

[0055] Step 4: Since I1=I2, R limit1 =R limit2 Differential op-amp output voltage U = G * (U + -U - =G*I1*R pt100 , to obtain R pt100 =G(U + -U - ) / I1, temperature T through R pt100 =R0*(1+A*T+B*T 2 +C*(T-100)*T 3 (R0=100Ω, A=3.9083e-3, B=-5.775e-7, C=-4.23225e-12, C=0 when T>0) The measurement is complete.

[0056] Among them, R limit1 R is the resistance value of current-limiting resistor 1. limit2 R is the resistance value of current-limiting resistor 2. lead1 R is the resistance value of lead resistor 1. lead2 R is the resistance of lead resistor 2. lead3 R is the resistance of lead resistor 3. pt100 It is a three-wire PT100 resistor.

[0057] like Figure 4 As shown, when PT100 is Figure 4 When the structure is connected, due to U + =I1*(R limit1 +R lead2 +R lead3 ), U - =I2*(R limit1 +R lead1 +R pt100 +R lead2 If the differential operational amplifier output voltage U = -G*I1*R, then the output voltage U = -G*I1*R. pt100 At this point, simply take the absolute value of the voltage in the processor and execute step 4 to complete the measurement.

[0058] like Figure 5 As shown, when PT100 is Figure 5When the structure is connected, if the switch is not switched, then U + =I1*(R limit1 +R lead3 +R pt100 +R lead1 +R limit2 ), U - =I2*(R lead2 +R pt100 +R lead1 +R limit2 If the differential operational amplifier output voltage U is... + -U - =I1*R limit1 =0.5*10=5mV <I1*R pt100 At this point, the MCU will assume that the PT100 is not correctly connected to the measurement circuit, and therefore will issue a switching command, turning it into... Figure 5 The current path is shown. Its calculation is... Figure 4 Similarly, this will not be elaborated upon here.

[0059] In summary, regardless of the wiring sequence of the PT100, this circuit scheme can complete the measurement of the resistance value of the RTD and can completely eliminate the error introduced by the lead resistance.

[0060] Through the above-described automatic detection circuit and method for the three-wire resistance temperature detector (RTD) circuit, the three wires of the RTD under test can be connected to ports 1, 2, and 3 of terminal 8 in any order, without needing to consider their electrical definitions, thus improving assembly convenience and effectively saving installation and debugging time. The first constant current source 1 is connected to a fixed port, and the second constant current source 2 can be selectively connected from ports 2 and 3 of terminal 8 through the first switching switch 5 and the second switching switch 6. Using two equal constant current sources (i.e., the first constant current source 1 and the second constant current source 2) as excitation to convert the resistance value of the RTD under test into a voltage signal has extremely high anti-interference capability. The difference in voltage signal is used to determine whether the RTD under test is correctly connected to the measurement circuit. If it is incorrect, it can be corrected by switching once. Furthermore, the measurement error introduced by the lead resistance can be eliminated.

[0061] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of this disclosure, "a plurality of" means two or more, unless otherwise explicitly specified.

[0062] In the embodiments of this disclosure, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this disclosure according to the specific circumstances.

[0063] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this disclosure. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0064] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the appended claims.

Claims

1. An automatic detection circuit for the wire sequence of a three-wire heating resistor, characterized in that, include: The output terminal of terminal block 1 is connected to the input terminal of the first current-limiting resistor; the output terminal of terminal block 2 is connected to the input terminal of the first switch; the output terminal of terminal block 3 is connected to the input terminal of the second switch; the output terminals of the first current-limiting resistor and the first constant current source are both connected to the positive input terminal of the differential operational amplifier; the normally closed pin of the first switch and the normally open pin of the second switch are both connected to the output terminal of the second constant current source; the normally open pin of the first switch and the normally closed pin of the second switch are connected in series with the second current-limiting resistor and grounded; and the normally open pin of the first switch and the normally closed pin of the second switch are both connected to the negative input terminal of the differential operational amplifier; the output terminal of the differential operational amplifier is connected to the input terminal of the analog-to-digital converter; the output terminal of the analog-to-digital converter is connected to the microprocessor; the microprocessor is electrically connected to the switch control unit; and the switch control unit is electrically connected to both the first switch and the second switch. The first constant current source is used to flow through the first current limiting resistor, port 1 of the terminal block, the thermal resistor to be tested, port 2 or 3 of the terminal block, the normally closed first switching switch, the second current limiting resistor, and ground to form a first current loop; the three wires of the three-wire thermal resistor to be tested are connected to port 1, port 2, and port 3 of the terminal block in any order. The second constant current source is used to flow through port 2 of the terminal block, the thermal resistor to be measured, port 3 of the terminal block, the normally closed second switching switch, the second current limiting resistor, and ground to form a second current loop; The first switching switch and the second switching switch are used to switch the two switches in response to the instructions of the microprocessor to change the flow direction of the second constant current source; The microprocessor is used to acquire temperature and voltage signals and take their absolute values. It determines whether the switching switch is activated based on the voltage value. When the voltage difference is less than the set threshold, it indicates that the wiring sequence does not meet the requirements. After switching, normal measurement can be achieved.

2. The automatic detection circuit for the three-wire heating resistor wire sequence according to claim 1, characterized in that, The first current-limiting resistor acts on the first current loop to prevent the first constant current source from short-circuiting to ground. The resistance value of the first current-limiting resistor is less than the resistance value corresponding to the lowest temperature in the ambient temperature range of the thermal resistor under test.

3. The automatic detection circuit for the three-wire heating resistor wire sequence according to claim 2, characterized in that, The second current-limiting resistor acts on the second current loop to prevent the second constant current source from short-circuiting to ground. The resistance value of the second current-limiting resistor is less than the resistance value corresponding to the lowest temperature in the ambient temperature range of the thermal resistor under test.

4. The automatic detection circuit for the three-wire heating resistor wire sequence according to claim 3, characterized in that, The normally closed terminal of the first switching switch and the normally open terminal of the second switching switch are connected to the second constant current source. The normally open terminal of the first switching switch and the normally closed terminal of the second switching switch are connected in series with a second current-limiting resistor and grounded. The two switch contacts are respectively connected to the other two ports occupied by the first constant current source.

5. The automatic detection circuit for the three-wire heating resistor wire sequence according to claim 4, characterized in that, The differential operational amplifier is used to amplify and condition the differential voltage signal across the resistor under test to the range of the analog-to-digital converter.

6. An automatic detection method for the wire sequence of a three-wire heating resistor, characterized in that, The method, applied to the automatic detection circuit for the three-wire heating resistor wire sequence of any one of claims 1 to 5, comprises: Connect the three wires of the RTD to be tested to ports 1, 2 and 3 of the terminal block respectively; wherein the first switch is normally closed and the second switch is normally open. When the circuit is powered on, the microprocessor performs a power-on self-test. This self-test includes reading the output voltage of the differential operational amplifier and determining whether the wiring is correct based on the voltage. If the voltage is greater than a set threshold, the three wires of the RTD under test are determined to be correctly connected. If the voltage is less than the set threshold, the three wires of the RTD under test are determined not to be correctly connected to the measurement circuit. In this case, the microprocessor sends an action command to the switch control unit to correct the wiring sequence. The switch control unit controls the first switch and the second switch to switch so that the first switch is normally open and the second switch is normally closed. The resistance of the thermal resistor to be measured can be obtained by taking the absolute value of the voltage, dividing it by the amplification factor of the differential operational amplifier, and then dividing it by the current of the first constant current source. The temperature value can then be obtained through the corresponding relationship.

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