Micro-resistance measuring circuit

Abstract

The utility model relates to a micro-resistance measuring circuit, which belongs to the technical field of micro-resistance measurement and comprises a single chip microcomputer, a controllable constant current source circuit, a detection circuit, a measured resistor and a fixed resistor. The single-chip microcomputer realizes a two-step measurement method by controlling the on-off of the controllable constant current source, the contact state of the measured resistor and whether the resistance value exceeds the range or not are judged through the suspended detection circuit, and the constant current source is started only in an effective range for accurate measurement. The fixed resistor enables the input voltage of the operational amplifier to be far away from a non-linear region, and the small signal measurement precision is improved. The dynamic zero-returning compensation module automatically deducts a fixed resistor and a line resistance value through a short-circuit detection terminal so as to realize high-precision compensation in a two-end measurement mode. A clamping diode and a two-stage low-pass filter are additionally arranged in the signal conditioning circuit, overvoltage and high-frequency interference are restrained, and sampling stability is ensured. The device has the advantages of low power consumption, high precision and simplified structure, and is suitable for rapid detection of micro-resistors such as glow plugs and the like.

Description

Technical Field

[0001] This utility model belongs to the field of micro resistance measurement technology, and specifically relates to a micro resistance measurement circuit. Background Technology

[0002] In industrial testing, microresistance measurement (such as glow plug resistance measurement) needs to balance accuracy and power consumption. Traditional solutions typically use a constant current source to continuously drive the resistor under test and eliminate line resistance errors through four-wire measurement, but this results in high overall power consumption and complex circuitry. Furthermore, four-wire systems require additional wiring, increasing costs. On the other hand, existing two-terminal measurement schemes are susceptible to the nonlinear characteristics of the operational amplifier near 0V, leading to poor stability in small-signal measurements. Therefore, there is an urgent need for a low-power, high-precision, and structurally simple microresistance detection solution. Utility Model Content

[0003] The purpose of this invention is to provide a micro-resistance measurement circuit to solve the problems mentioned in the background art.

[0004] To achieve the above objectives, this utility model provides the following technical solution:

[0005] A microresistance measurement circuit includes a microcontroller, a controllable constant current source circuit, a detection circuit, a resistor to be measured, and a fixed resistor; wherein:

[0006] One end of the resistor under test is connected to the output of the controllable constant current source circuit through the REDI N node, and the other end of the resistor under test is connected to one end of the fixed resistor through the BLACKI N node. The other end of the fixed resistor is grounded.

[0007] The control input terminal of the controllable constant current source circuit is connected to the control output terminal of the microcontroller, which is used to control the opening and closing of the controllable constant current source circuit.

[0008] The detection circuit includes a floating detection circuit and a signal conditioning circuit:

[0009] The input terminal of the floating detection circuit is connected to the floating detection output terminal of the microcontroller, and the output terminal of the floating detection circuit is connected to the REDI N node. The floating detection circuit and the microcontroller work together to detect the contact state of the resistor under test and whether the resistance value of the resistor under test exceeds the preset range.

[0010] The signal conditioning circuit includes a second amplifier. The input of the signal conditioning circuit is connected to the REDI N node, and the output of the signal conditioning circuit is connected to the analog-to-digital converter port of the microcontroller. The signal conditioning circuit is used to acquire and amplify voltage signals. Fixed resistors are used to avoid the nonlinear operating region of the second amplifier.

[0011] The microcontroller includes a dynamic zero-homing compensation module, which records the total voltage drop of the fixed resistor and the line resistance, and obtains the actual resistance value of the measured resistor by subtracting the total voltage drop.

[0012] The contact status of the resistor under test and whether it is within the range are roughly measured by the floating detection circuit. If it is within the range, the constant current source circuit is started. By shorting the nodes at both ends of the resistor under test, the line resistance of the system itself (including the fixed resistor) is measured. Finally, the voltage drop after the resistor under test is connected is measured to obtain the resistance value of the resistor under test.

[0013] Preferably, the controllable constant current source circuit includes a first amplifier, a first diode, a first transistor, and a second transistor;

[0014] The non-inverting input terminal of the first amplifier is grounded through the ninth resistor and connected to the positive terminal of the power supply through the fifth resistor. The inverting input terminal of the first amplifier is connected to the collector of the second transistor. The output terminal of the first amplifier is connected to the base of the first transistor through the seventh resistor. The output terminal of the first amplifier is connected to one end of the sixth resistor. The other end of the sixth resistor is connected to the positive terminal of the power supply and one end of the second resistor. The other end of the second resistor is connected to the emitter of the first transistor and one end of the third resistor. The other end of the third resistor is connected to the collector of the second transistor. The power supply terminal of the first amplifier is connected to the positive terminal of the power supply. The ground terminal of the first amplifier is grounded.

[0015] The collector of the first transistor is grounded through the first capacitor and connected to the REDI N node through a positive temperature coefficient thermistor.

[0016] The anode of the first diode is grounded, and the cathode of the first diode is connected to the positive terminal of the power supply through the first resistor and to the collector of the second transistor through the fourth resistor.

[0017] The base of the second transistor is connected to the control output terminal of the microcontroller through the eighth resistor, and the emitter of the second transistor is grounded.

[0018] Preferably, the third and fourth resistors are megohm-level resistors.

[0019] Preferably, the first diode is a Zener diode.

[0020] Preferably, the suspension detection circuit includes a second diode and a twelfth resistor;

[0021] One end of the twelfth resistor is connected to the floating detection output terminal of the microcontroller, and the other end of the twelfth resistor is connected to the anode of the second diode, and the cathode of the second diode is connected to the REDIN node.

[0022] Preferably, the signal conditioning circuit includes a second amplifier, a tenth resistor, an eleventh resistor, and a thirteenth resistor;

[0023] The non-inverting input of the second amplifier is connected to the REDIN node through the thirteenth resistor. The inverting input of the second amplifier is connected to one end of the tenth resistor and one end of the eleventh resistor, respectively. The other end of the tenth resistor is grounded, and the other end of the eleventh resistor is connected to the output of the second amplifier and the analog-to-digital converter port of the microcontroller, respectively.

[0024] Preferably, the signal conditioning circuit further includes a third diode and a fourth diode;

[0025] The anode of the third diode is connected to one end of the thirteenth resistor, the cathode of the fourth diode, and the non-inverting input of the second amplifier. The cathode of the third diode is connected to the positive terminal of the power supply, and the anode of the fourth diode is grounded.

[0026] Preferably, the detection circuit further includes two stages of low-pass filtering, wherein;

[0027] The first-stage low-pass filter includes a second capacitor. One end of the second capacitor is connected to the inverting input of the second amplifier, and the other end of the second capacitor is connected to the output of the second amplifier.

[0028] The second-stage low-pass filter includes a third capacitor and a fourteenth resistor. The fourteenth resistor is located between the output of the second amplifier and the analog-to-digital converter port of the microcontroller. One end of the third capacitor is connected to the analog-to-digital converter port of the microcontroller, and the other end of the third capacitor is grounded.

[0029] Preferably, the dynamic zero-return compensation module obtains the total voltage drop of the fixed resistance and line resistance by shorting the REDIN node and the BLACKIN node.

[0030] Preferably, the micro-resistance measurement circuit further includes a first circuit breaker connected in parallel with the resistor being measured, used to short-circuit the REDIN node and the BLACKIN node.

[0031] Compared with the prior art, the beneficial effects of this utility model are:

[0032] 1. Two-step measurement method:

[0033] Coarse measurement (floating detection): The floating detection circuit quickly determines the contact status of the resistor being measured and whether it is within the range, avoiding unnecessary power consumption.

[0034] Precision Measurement (Constant Current Drive): Enables high-precision measurement only within the effective range, starts the constant current source, and reduces the overall power consumption.

[0035] 2. The introduction of a fixed resistor raises the op-amp input voltage to the linear operating region, improving the stability of small-signal measurements.

[0036] 3. A zero-return mechanism is used to dynamically calibrate the fixed resistor and line resistance, enabling two-terminal measurement with four-wire accuracy, simplifying the structure while maintaining accuracy.

[0037] 4. The diode clamping voltage and multi-stage filtering settings ensure signal integrity and enhance system robustness. Attached Figure Description

[0038] Figure 1 This is a block diagram illustrating the measurement principle of this utility model;

[0039] Figure 2 This is a circuit diagram of a controllable constant current source;

[0040] Figure 3 Circuit diagram for testing;

[0041] Figure 4 The circuit structure diagram shows the short-circuit REDI N node and BLACKI N node. Detailed Implementation

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

[0043] It should be understood that the step numbers used in the text are for ease of description only and are not intended to limit the order in which the steps are performed.

[0044] It should be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the scope of the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0045] The terms “comprising” and “including” indicate the presence of the described feature, whole, step, operation, element and / or component, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or collections thereof.

[0046] The term “and / or” refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes these combinations.

[0047] In this embodiment, the microcontroller is model HC89S003, and the first amplifier and the second amplifier are model MCP6002.

[0048] As attached Figure 1 As shown, a micro-resistance measurement circuit includes a microcontroller, a controllable constant current source circuit, a detection circuit, a resistor to be measured Rx, and a fixed resistor R15; wherein:

[0049] One end of the resistor being measured, Rx, is connected to the output of the controllable constant current source circuit through the REDIN node, and the other end of the resistor being measured is connected to one end of the fixed resistor R15 through the BLACKIN node. The other end of the fixed resistor R15 is grounded.

[0050] The control input terminal of the controllable constant current source circuit is connected to the control output terminal AMPCTRL of the microcontroller. The microcontroller is used to control the opening and closing of the controllable constant current source circuit.

[0051] The detection circuit includes a floating detection circuit and a signal conditioning circuit:

[0052] The input terminal of the floating detection circuit is connected to the floating detection output terminal JUDGEPEN of the microcontroller, and the output terminal of the floating detection circuit is connected to the REDIN node. The floating detection circuit and the microcontroller work together to detect the contact status of the resistor Rx under test and whether the resistance value of the resistor Rx under test exceeds the preset range.

[0053] The signal conditioning circuit includes a second amplifier U1.2. The input terminal of the signal conditioning circuit is connected to the REDIN node, and the output terminal of the signal conditioning circuit is connected to the analog-to-digital conversion port AD1 of the microcontroller. The signal conditioning circuit is used to acquire and amplify voltage signals. The fixed resistor R15 is used to avoid the nonlinear operating region of the second amplifier U1.2.

[0054] The microcontroller includes a dynamic zero-homing compensation module, which records the total voltage drop of the fixed resistor R15 and the line resistance, and obtains the actual resistance value of the measured resistor Rx by subtracting the total voltage drop.

[0055] As a preferred embodiment of this utility model, see attached... Figure 2 As shown, the controllable constant current source circuit includes a first amplifier U1.1, a first diode D1, a first transistor Q1, and a second transistor Q2;

[0056] The non-inverting input of the first amplifier U1.1 is grounded through the ninth resistor R9 and connected to the positive power supply through the fifth resistor R5. The inverting input of the first amplifier U1.1 is connected to the collector of the second transistor Q2. The output of the first amplifier U1.1 is connected to the base of the first transistor Q1 through the seventh resistor R7. The output of the first amplifier U1.1 is also connected to one end of the sixth resistor R6. The other end of the sixth resistor R6 is connected to the positive power supply and one end of the second resistor R2. The other end of the second resistor R2 is connected to the emitter of the first transistor Q1 and one end of the third resistor R3. The other end of the third resistor R3 is connected to the collector of the second transistor Q2. The power supply terminal of the first amplifier U1.1 is connected to the positive power supply, and the ground terminal of the first amplifier U1.1 is grounded.

[0057] The collector of the first transistor Q1 is grounded through the first capacitor C1 and connected to the RED IN node through the positive temperature coefficient thermistor PTC1.

[0058] The anode of the first diode D1 is grounded, and the cathode of the first diode D1 is connected to the positive terminal of the power supply through the first resistor R1 and to the collector of the second transistor Q2 through the fourth resistor R4.

[0059] The base of the second transistor Q2 is connected to the control output terminal AMPCTRL of the microcontroller through the eighth resistor R8, and the emitter of the second transistor Q2 is grounded.

[0060] In a preferred embodiment of this utility model, the third resistor R3 and the fourth resistor R4 are megohm-level resistors.

[0061] In a preferred embodiment of this utility model, the first diode D1 is a Zener diode.

[0062] The specific working principle of the controllable constant current source circuit is as follows:

[0063] When the microcontroller's control output terminal AMPCTRL is low under the microcontroller's control, the second transistor Q2 is cut off, and the constant current source outputs current to the RED IN node; when the microcontroller's control output terminal AMPCTRL is high under the microcontroller's control, the first amplifier U1.1 is in a forward bias state, and the constant current flowing through the second resistor R2 drops to zero, thus turning off the constant current source; specifically:

[0064] The controllable constant current source circuit stabilizes the voltage to the left of the first diode D1 to 1.2V through the loop formed by the first resistor R1 and the first diode D1. The fifth resistor R5 and the ninth resistor R9 form a voltage divider circuit to divide the 5V to 2.5V as the input of the non-inverting input terminal of the first amplifier U1.1. When the control output terminal AMPCTRL of the microcontroller connected to the control terminal of the controllable constant current source circuit is low, the second transistor Q2 is cut off. The first amplifier U1.1, the sixth resistor R6, the seventh resistor R7, and the first transistor Q1 form the output drive circuit. The output voltage of the first amplifier U1.1 is generated by the output drive circuit and then divided by the third resistor R3 and the fourth resistor R4 before being fed back to the inverting input terminal of the first amplifier U1.1. Therefore, the voltage value of the right pin of the second resistor R2 is a fixed value of 0V. The 5V is released as a constant current value to the 0V node through the second resistor R2. The third resistor R3 and the fourth resistor R4 are megohm-level high-resistance resistors, and the current flowing through the voltage divider network is extremely small. Therefore, the constant current flows through the first transistor Q1 and the positive temperature coefficient thermistor PTC1 and is output from the REDIN node. When the control output terminal AMPCTRL of the microcontroller connected to the control terminal of the controllable constant current source circuit is high, the first amplifier U1.1 is in a forward bias state and outputs a 5V voltage. The second transistor Q2 is turned on, and the collector voltage of the second transistor Q2 is pulled down to 0V, causing the voltage difference across the second resistor R2 to disappear, the constant current is terminated, and the constant current source is turned off.

[0065] In a preferred embodiment of the present invention, the suspension detection circuit includes a second diode D2 and a twelfth resistor R12;

[0066] One end of the twelfth resistor R12 is connected to the floating detection output terminal JUDGEPEN of the microcontroller, and the other end of the twelfth resistor R12 is connected to the anode of the second diode D2. The cathode of the second diode D2 is connected to the REDIN node.

[0067] The process of the floating detection circuit for detecting the contact state of the resistor Rx under test is as follows: The microcontroller periodically sets the floating detection output terminal JUDGEPEN to a high level, and determines whether the contact state of the resistor Rx under test exceeds the preset range by detecting the level state of the analog-to-digital converter port AD1 of the microcontroller. Specifically:

[0068] When the measured resistor Rx is floating or the resistance value of the measured resistor Rx exceeds the preset value (the preset value is set to 50Ω in this embodiment), the analog-to-digital conversion port AD1 of the microcontroller detects a high level, which is determined to be an invalid measurement state (i.e. Rx is open or over the range), and the constant current source is kept off.

[0069] When the resistance value of the resistor being measured, Rx, is within the effective range, the analog-to-digital converter port AD1 of the microcontroller detects a low level, which is determined to be a valid measurement state. The floating detection output terminal JUDGEPEN of the microcontroller is set to a low level, and the constant current source is started to enter the precise measurement stage.

[0070] In a preferred embodiment of this utility model, the signal conditioning circuit includes a second amplifier U1.2, a tenth resistor R10, an eleventh resistor R11, and a thirteenth resistor R13;

[0071] The non-inverting input of the second amplifier U1.2 is connected to the REDIN node through the thirteenth resistor R13. The inverting input of the second amplifier U1.2 is connected to one end of the tenth resistor R10 and one end of the eleventh resistor R11. The other end of the tenth resistor R10 is grounded. The other end of the eleventh resistor R11 is connected to the output of the second amplifier U1.2 and the analog-to-digital converter port AD1 of the microcontroller.

[0072] The second amplifier U1.2, the tenth resistor R10, and the eleventh resistor R11 form a proportional amplifier circuit to amplify the input voltage of the detection circuit. The amplified voltage is then sent to the microcontroller via the analog-to-digital converter port AD1 for AD conversion, thus enabling resistance detection. The thirteenth resistor R13 limits the input current of the second amplifier U1.2.

[0073] In a preferred embodiment of the present invention, the signal conditioning circuit further includes a third diode D3 and a fourth diode D4;

[0074] The anode of the third diode D3 is connected to one end of the thirteenth resistor R13, the cathode of the fourth diode D4, and the non-inverting input terminal of the second amplifier U1.2. The cathode of the third diode D3 is connected to the positive terminal of the power supply, and the anode of the fourth diode D4 is grounded.

[0075] The third diode D3 and the fourth diode D4 are used to clamp the voltage to the range of -0.7V to 5.7V to prevent overvoltage at the input of the second amplifier U1.2.

[0076] In a preferred embodiment of this utility model, the detection circuit further includes two stages of low-pass filtering, wherein;

[0077] The first-stage low-pass filter includes a second capacitor C2. One end of the second capacitor C2 is connected to the inverting input terminal of the second amplifier U1.2, and the other end of the second capacitor C2 is connected to the output terminal of the second amplifier U1.2.

[0078] The second-stage low-pass filter includes a third capacitor C3 and a fourteenth resistor R14. The fourteenth resistor R14 is located between the output of the second amplifier U1.2 and the analog-to-digital converter port AD1 of the microcontroller. One end of the third capacitor C3 is connected to the analog-to-digital converter port AD1 of the microcontroller, and the other end of the third capacitor C3 is grounded.

[0079] High-frequency noise is suppressed by two-stage low-pass filtering, stabilizing the sampling of the microcontroller's analog-to-digital converter port AD1.

[0080] In a preferred embodiment of this utility model, the dynamic zero-return compensation module obtains the total voltage drop of the fixed resistance and line resistance by shorting the REDIN node and the BLACKIN node. The specific working logic is as follows:

[0081] In this embodiment, when the dynamic zero-return compensation module measures the fixed resistor R15 and the line resistance, the REDIN and BLACKIN nodes are shorted. During the dynamic zero-return compensation operation, the REDIN and BLACKIN nodes are shorted, and the total voltage drop value of the fixed resistor R15 and the line resistance is measured and stored.

[0082] In a preferred embodiment of the present invention, the micro-resistance measurement circuit further includes a first circuit breaker QF, which is connected in parallel with the resistor being measured Rx and is used to short-circuit the REDIN node and the BLACKIN node.

[0083] As attached Figure 4 As shown, the first circuit breaker QF can achieve the effect of short-circuiting the REDIN and BLACKIN nodes. When measuring the total voltage drop of the fixed resistor R15 and the line resistance, the first circuit breaker QF closes. During actual measurement, the first circuit breaker QF opens.

[0084] In actual measurement, the actual resistance value of the resistor being measured, Rx, is obtained by subtracting the total voltage drop value.

[0085] In this application embodiment, "at least one" refers to one or more, and "more than one" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent the existence of A alone, A and B simultaneously, or B alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one of the following" and similar expressions refer to any combination of these items, including any combination of singular or plural items. For example, at least one of a, b, and c can represent: a, b, c, a and b, a and c, b and c, or a and b and c, where a, b, and c can be single or multiple.

[0086] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A micro-ohmmeter circuit, comprising: It includes a microcontroller, a controllable constant current source circuit, a detection circuit, the resistor to be measured, and a fixed resistor; among which: One end of the resistor under test is connected to the output of the controllable constant current source circuit through the REDI N node, and the other end of the resistor under test is connected to one end of the fixed resistor through the BLACKI N node. The other end of the fixed resistor is grounded. The control input terminal of the controllable constant current source circuit is connected to the control output terminal of the microcontroller, which is used to control the opening and closing of the controllable constant current source circuit. The detection circuit includes a floating detection circuit and a signal conditioning circuit: The input terminal of the floating detection circuit is connected to the floating detection output terminal of the microcontroller, and the output terminal of the floating detection circuit is connected to the REDI N node to detect the contact status of the resistor under test and whether the resistance value of the resistor under test exceeds the preset range. The signal conditioning circuit includes a second amplifier. The input of the signal conditioning circuit is connected to the REDI N node, and the output of the signal conditioning circuit is connected to the analog-to-digital converter port of the microcontroller. The signal conditioning circuit is used to acquire and amplify voltage signals. Fixed resistors are used to avoid the nonlinear operating region of the second amplifier. The microcontroller includes a dynamic zero-homing compensation module, which records the total voltage drop of the fixed resistor and the line resistance, and obtains the actual resistance value of the measured resistor by subtracting the total voltage drop.

2. The microresistance measurement circuit according to claim 1, characterized in that: The controllable constant current source circuit includes a first amplifier, a first diode, a first transistor, and a second transistor; The non-inverting input terminal of the first amplifier is grounded through the ninth resistor and connected to the positive terminal of the power supply through the fifth resistor. The inverting input terminal of the first amplifier is connected to the collector of the second transistor. The output terminal of the first amplifier is connected to the base of the first transistor through the seventh resistor. The output terminal of the first amplifier is connected to one end of the sixth resistor. The other end of the sixth resistor is connected to the positive terminal of the power supply and one end of the second resistor. The other end of the second resistor is connected to the emitter of the first transistor and one end of the third resistor. The other end of the third resistor is connected to the collector of the second transistor. The power supply terminal of the first amplifier is connected to the positive terminal of the power supply. The ground terminal of the first amplifier is grounded. The collector of the first transistor is grounded through the first capacitor and connected to the REDIN node through a positive temperature coefficient thermistor. The anode of the first diode is grounded, and the cathode of the first diode is connected to the positive terminal of the power supply through the first resistor and to the collector of the second transistor through the fourth resistor. The base of the second transistor is connected to the control output terminal of the microcontroller through the eighth resistor, and the emitter of the second transistor is grounded.

3. The micro-resistance measurement circuit according to claim 2, characterized in that: The third and fourth resistors are megohm-level resistors.

4. The micro-resistance measurement circuit according to claim 2, characterized in that: The first diode is a Zener diode.

5. A micro-resistance measurement circuit according to claim 1, characterized in that: The suspension detection circuit includes a second diode and a twelfth resistor; One end of the twelfth resistor is connected to the floating detection output terminal of the microcontroller, and the other end of the twelfth resistor is connected to the anode of the second diode, and the cathode of the second diode is connected to the REDIN node.

6. The micro-resistance measurement circuit according to claim 1, characterized in that: The signal conditioning circuit includes a second amplifier, a tenth resistor, an eleventh resistor, and a thirteenth resistor; The non-inverting input of the second amplifier is connected to the REDIN node through the thirteenth resistor. The inverting input of the second amplifier is connected to one end of the tenth resistor and one end of the eleventh resistor, respectively. The other end of the tenth resistor is grounded, and the other end of the eleventh resistor is connected to the output of the second amplifier and the analog-to-digital converter port of the microcontroller, respectively.

7. A micro-resistance measurement circuit according to claim 6, characterized in that: The signal conditioning circuit also includes a third diode and a fourth diode; The anode of the third diode is connected to one end of the thirteenth resistor, the cathode of the fourth diode, and the non-inverting input of the second amplifier. The cathode of the third diode is connected to the positive terminal of the power supply, and the anode of the fourth diode is grounded.

8. A micro-resistance measurement circuit according to claim 6, characterized in that: The detection circuit also includes two stages of low-pass filtering, wherein; The first-stage low-pass filter includes a second capacitor. One end of the second capacitor is connected to the inverting input of the second amplifier, and the other end of the second capacitor is connected to the output of the second amplifier. The second-stage low-pass filter includes a third capacitor and a fourteenth resistor. The fourteenth resistor is located between the output of the second amplifier and the analog-to-digital converter port of the microcontroller. One end of the third capacitor is connected to the analog-to-digital converter port of the microcontroller, and the other end of the third capacitor is grounded.

9. A micro-resistance measurement circuit according to claim 1, characterized in that: The dynamic zero-return compensation module obtains the total voltage drop of the fixed resistance and line resistance by shorting the REDIN node and BLACKIN node.

10. A micro-resistance measurement circuit according to claim 1 or 9, characterized in that: The micro-resistance measurement circuit also includes a first circuit breaker, which is connected in parallel with the resistor being measured and is used to short-circuit the REDIN node and the BLACKIN node.

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