Direct current micro-resistance measuring device with anti-thermal electromotive force interference

Abstract

The utility model discloses a kind of DC micro-resistance measuring devices of thermal electromotive force interference resistance, the device is by setting bidirectional program-controlled constant current source module, current direction switching module, voltage sampling module and signal processing module, the alternating application and voltage sampling to the positive and negative current of measured piece are realized, eliminate electromotive force influence by positive and negative voltage difference calculation, the precision and stability of small resistance measurement are significantly improved. It is suitable for the high-precision measurement of small resistance in the range of 1uΩ-100uΩ of transformer winding, new energy automobile welding parts etc.

Description

Technical Field

[0001] This utility model relates to the field of DC resistance measurement technology, and in particular to a DC micro-resistance measuring device that is resistant to thermoelectric interference. Background Technology

[0002] In DC resistance measurement, especially in scenarios involving minute resistances from 1µΩ to 100µΩ (such as transformer windings and welded components in new energy vehicles), factors such as the metal-to-metal contact between the measured component and the measuring fixture, and temperature differences, generate an electromotive force (Vemf), leading to measurement errors. Existing technologies often employ a "two-stage sampling" method (current switching on and off) to eliminate the Vemf. However, temperature changes in the measured component after the current is turned off alter the Vemf, resulting in insufficient compensation accuracy. For example, when measuring a 1mΩ resistor, a 10µV Vemf measurement with a 1A current will produce a 1% error; however, for a 1µΩ resistor, the same Vemf will lead to a 1000% error, severely impacting measurement reliability. Therefore, a more accurate measuring device for eliminating Vemf is urgently needed. Utility Model Content

[0003] To address the technical problems existing in the background art, this utility model proposes a DC micro-resistance measuring device that is resistant to thermoelectric potential interference.

[0004] This utility model proposes a DC micro-resistance measuring device resistant to thermoelectric interference, comprising:

[0005] A bidirectional programmable constant current source module is used to alternately output a positive constant current and a reverse constant current with equal absolute values ​​to the device under test;

[0006] A current direction switching module is connected between the programmable constant current source module and the device under test (DUT) to switch the direction of the current output to the DUT, thereby enabling the alternating application of forward and reverse current.

[0007] The voltage sampling module is connected to both ends of the device under test and is used to collect the voltage V1 when a forward current flows through the device under test and the voltage V2 when a reverse current flows through the device under test.

[0008] The signal processing module is electrically connected to the programmable constant current source module, the current direction switching module, and the sampling module, respectively, and is used to control the switching timing of the current direction switching module; at the same time, it receives the voltage V1 and voltage V2, and calculates the resistance value of the device under test based on the absolute value of the forward constant current or the reverse constant current, combined with the difference between voltage V1 and voltage V2.

[0009] Preferably, the bidirectional programmable constant current source module includes a reference constant current source, a resistor R1, a voltage inverter U1, and an operational amplifier U3; the reference constant current source generates a positive reference voltage through R1, and the voltage inverter U1 converts the positive reference voltage into a reverse reference voltage; the operational amplifier U3 is used to condition the reference voltage and provide an input signal for subsequent current amplification.

[0010] Preferably, the current direction switching module includes a three-channel single-pole double-throw analog switch U2. The input terminals of the analog switch U2 are respectively connected to the forward reference voltage, the reverse reference voltage, and the 0V voltage. The output terminal of the analog switch U2 is connected to the non-inverting input terminal of the operational amplifier U3. By controlling the control terminal BA of the analog switch U2, the switching between forward current, reverse current, and stop can be realized.

[0011] Preferably, the bidirectional programmable constant current source module further includes a current amplification circuit, which includes a current-limiting resistor R4, a current-limiting resistor R5, a negative feedback capacitor C9, and a transistor amplification unit. The transistor amplification unit includes transistors Q1-Q4. Transistor Q1 drives transistor Q2 to form a forward path, and transistor Q3 drives transistor Q4 to form a reverse path. A current-limiting resistor R4 is connected in series between the output terminal of operational amplifier U3 and the base of transistor Q1. One end of the negative feedback capacitor C9 is electrically connected to the inverting input terminal of operational amplifier U3, and the other end of the negative feedback capacitor C9 is connected in series with the current-limiting resistor R5 and then connected to the base of transistor Q3.

[0012] Preferably, the current amplification circuit further includes a sampling resistor R2 and a resistor R3; the sampling resistor R2 is connected in series between the device under test and ground, and the voltage across the sampling resistor R2 is fed back to the inverting input of the operational amplifier U3 through the resistor R3, forming a deep negative feedback.

[0013] Preferably, transistors Q1 and Q2 are NPN transistors, and transistors Q3 and Q4 are PNP transistors.

[0014] Preferably, the voltage sampling module includes an analog switch U7, an operational amplifier U4, an operational amplifier U5, and an ADC module U8; the analog switch U7 is used to switch the sampling of one end SENSE+ and the other end SENSE- of the device under test; the operational amplifiers U4 and U5 are used to follow and condition the sampled voltage; the ADC module U8 is used to convert the conditioned analog voltage into a digital signal, and a +2.5V bias voltage is superimposed on the input terminal of the ADC module U8.

[0015] Preferably, the differential input voltage of the ADC module U8 is 0.9 times the conditioned voltage, and the ADC module U8 transmits the digital signal to the signal processing module through the SPI interface.

[0016] The proposed DC micro-resistance measuring device, which is resistant to thermoelectric electromotive force interference, directly cancels the electromotive force Vemf and the voltmeter bias voltage by calculating the difference between forward and reverse current sampling, thus avoiding the influence of electromotive force changes after the current is turned off and improving the compensation accuracy. It is suitable for measuring micro-resistances from 1uΩ to 100uΩ, meeting the high-precision testing requirements of welding parts for new energy vehicles, transformer windings, etc. It adopts a low-temperature drift resistor, charge balance converter and negative feedback design to ensure stable 1A constant current output and improve anti-interference capability. Attached Figure Description

[0017] Figure 1 This is a schematic diagram illustrating the measurement principle of a DC micro-resistance measuring device resistant to thermoelectric potential interference proposed in this utility model.

[0018] Figure 2 A partial architecture diagram of a DC micro-resistance measuring device resistant to thermoelectric potential interference proposed in this utility model. Figure 1 ;

[0019] Figure 3 The timing diagram for the current direction switching control of a DC micro-resistance measuring device resistant to thermoelectric interference proposed in this utility model;

[0020] Figure 4 The timing diagram of current output during the measurement cycle of a DC micro-resistance measuring device that resists thermoelectric potential interference proposed in this utility model;

[0021] Figure 5 A partial architecture diagram of a DC micro-resistance measuring device resistant to thermoelectric potential interference proposed in this utility model. Figure 2 . Detailed Implementation

[0022] Reference Figure 1-5 The present invention proposes a DC micro-resistance measuring device resistant to thermoelectric interference, comprising:

[0023] The bidirectional programmable constant current source module is used to alternately output a positive constant current and a reverse constant current with equal absolute values ​​to the device under test.

[0024] Specifically, in this embodiment, the resistance of the device under test ranges from 1uΩ to 100uΩ.

[0025] In this embodiment, the bidirectional programmable constant current source module includes a reference constant current source, a resistor R1, a voltage inverter U1, and an operational amplifier U3. The reference constant current source generates a positive reference voltage through R1, and the voltage inverter U1 converts the positive reference voltage into a reverse reference voltage. The operational amplifier U3 is used to condition the reference voltage and provide an input signal for subsequent current amplification.

[0026] In this embodiment, the bidirectional programmable constant current source module further includes a current amplification circuit, which includes a current-limiting resistor R4, a current-limiting resistor R5, a negative feedback capacitor C9, and a transistor amplification unit. The transistor amplification unit includes transistors Q1-Q4. Transistor Q1 drives transistor Q2 to form a forward path, and transistor Q3 drives transistor Q4 to form a reverse path. A current-limiting resistor R4 is connected in series between the output terminal of operational amplifier U3 and the base of transistor Q1. One end of the negative feedback capacitor C9 is electrically connected to the inverting input terminal of operational amplifier U3, and the other end of the negative feedback capacitor C9 is connected in series with the current-limiting resistor R5 and then connected to the base of transistor Q3.

[0027] Specifically, such as Figure 2 As shown, the bidirectional programmable constant current source module includes a 0.1mA reference constant current source, resistor R1 (1kΩ), voltage inverter U1 (LTC1403CSW), and operational amplifier U3 (LTC1050CS8). The 0.1mA reference constant current flows through R1 to generate a 0.1V reference voltage (V=I×R=0.1mA×1kΩ=0.1V); the voltage inverter U1 converts 0.1V to -0.1V, providing a reference for the reverse current; the operational amplifier U3 stabilizes the output voltage through negative feedback, providing a stable input for subsequent current amplification. The current amplification circuit consists of two stages of emitter followers composed of transistors Q1-Q4: positive voltage is amplified by Q1 and Q2 to output a positive current, and negative voltage is amplified by Q3 and Q4 to output a reverse current, ultimately achieving a 1A constant current output (stabilized by feedback from sampling resistor R2 (0.1Ω): I=V / R=0.1V / 0.1Ω=1A).

[0028] The current direction switching module is connected between the programmable constant current source module and the device under test (DUT) to switch the direction of the current output to the DUT, thereby enabling the alternating application of forward and reverse current.

[0029] In this embodiment, the current direction switching module includes a three-channel single-pole double-throw analog switch U2. The input terminals of the analog switch U2 are connected to the forward reference voltage, the reverse reference voltage, and the 0V voltage, respectively. The output terminal of the analog switch U2 is connected to the non-inverting input terminal of the operational amplifier U3. By controlling the control terminal BA of the analog switch U2, the switching between forward current, reverse current, and stop is realized.

[0030] Specifically, such as Figure 2 and Figure 3 As shown, the current direction switching module uses a three-channel single-pole double-throw analog switch U2 (74HCT4053PW). The reference voltage input to the non-inverting terminal of U3 is switched through the control terminal BA. When BA=00, the reference input is 0.1V and the output current is 1A in the forward direction; when BA=10, the reference input is -0.1V and the output current is 1A in the reverse direction; when BA=01, the input is 0V and the output current stops.

[0031] The voltage sampling module is connected to both ends of the device under test (DUT) and is used to collect the voltage V1 when a forward current flows through the DUT and the voltage V2 when a reverse current flows through the DUT.

[0032] In this embodiment, the voltage sampling module includes an analog switch U7, an operational amplifier U4, an operational amplifier U5, and an ADC module U8. The analog switch U7 is used to switch the sampling of one end SENSE+ and the other end SENSE- of the device under test. The operational amplifiers U4 and U5 are used to follow and condition the sampled voltage. The ADC module U8 is used to convert the conditioned analog voltage into a digital signal, and a +2.5V bias voltage is superimposed on the input of the ADC module U8.

[0033] In this embodiment, the differential input voltage of the ADC module U8 is 0.9 times the conditioned voltage, and the ADC module U8 transmits the digital signal to the signal processing module through the SPI interface.

[0034] Specifically, such as Figure 5 As shown, U7 switches the voltage sampling of one end SENSE+ and the other end SENSE- of the device under test; operational amplifiers U4 and U5 follow and condition the sampled voltage, scaling the signal to the ADC adaptation range; since U8 is powered by a single power supply, the sampled negative voltage needs to be superimposed with a +2.5V bias to ensure that the ADC input common-mode voltage is positive.

[0035] The signal processing module is electrically connected to the programmable constant current source module, the current direction switching module, and the sampling module, respectively, and is used to control the switching timing of the current direction switching module; at the same time, it receives voltage V1 and voltage V2, and calculates the resistance value of the device under test based on the absolute value of the forward constant current or the reverse constant current, combined with the difference between voltage V1 and voltage V2.

[0036] In this embodiment, the formula for calculating the resistance value of the device under test is: Rx=(V1-V2) / (2×Im), where Im is the constant current value output by the bidirectional programmable constant current source module; Rx is the resistance value of the device under test.

[0037] Specifically, the signal processing module uses a microcontroller to receive the digital signal output by the ADC via the SPI interface, calculates the forward voltage V1 and reverse voltage V2, and calculates the resistance value of the device under test using the formula Rx = (V1 - V2) / (2 × 1A), where Rx is the resistance value of the device under test. Since V1 = Rx × 1A + Vemf and V2 = -Rx × 1A + Vemf, the difference V1 - V2 = 2Rx × 1A can completely cancel out Vemf, achieving accurate measurement.

[0038] In this embodiment, the current amplification circuit also includes a sampling resistor R2 and a resistor R3; the sampling resistor R2 is connected in series between the device under test and ground, and the voltage across the sampling resistor R2 is fed back to the inverting input of the operational amplifier U3 through the resistor R3, forming a deep negative feedback.

[0039] Specifically, transistors Q1 and Q2 are NPN transistors, while transistors Q3 and Q4 are PNP transistors.

[0040] In this embodiment, as Figure 1-5 As shown, the working process of the bidirectional programmable constant current source module is as follows: a 0.1mA reference constant current flows through R1 to generate a 0.1V voltage, which is then inverted by U1 to obtain -0.1V; U2 switches the reference voltage to the non-inverting input of U3, and the output signal of U3 is amplified into a 1A current by Q1-Q4. Current stability is ensured through negative feedback (the sampled voltage of R2 is fed back to the inverting input of U3). The working process of the current direction switching module is as follows: the microcontroller controls the BA terminal of U2: when BA=00, it outputs a positive 1A current; when BA=10, it outputs a reverse 1A current. The switching between positive, reverse, and zero current is completed within one measurement cycle. Figure 4 As shown. The specific working process of the voltage sampling module and signal processing module is as follows: When the current is forward, the sampling module obtains V1 = Rx × 1A + Vemf; when the current is reverse, it obtains V2 = -Rx × 1A + Vemf; the microcontroller calculates Rx = (V1 - V2) / (2 × 1A), where Rx is the resistance value of the device under test, eliminates Vemf interference, and outputs the true resistance value of the device under test.

[0041] The above description is only a preferred embodiment of the present utility model, but the protection scope of the present utility model is not limited thereto. Any equivalent substitutions or changes made by those skilled in the art within the technical scope disclosed in the present utility model, based on the technical solution and the inventive concept of the present utility model, should be included within the protection scope of the present utility model.

Claims

1. A DC micro-resistance measuring device resistant to thermoelectric potential interference, characterized in that, include: A bidirectional programmable constant current source module is used to alternately output a positive constant current and a reverse constant current with equal absolute values ​​to the device under test; A current direction switching module is connected between the programmable constant current source module and the device under test (DUT) to switch the direction of the current output to the DUT, thereby enabling the alternating application of forward and reverse current. The voltage sampling module is connected to both ends of the device under test and is used to collect the voltage V1 when a forward current flows through the device under test and the voltage V2 when a reverse current flows through the device under test. The signal processing module is electrically connected to the programmable constant current source module, the current direction switching module, and the sampling module, respectively, and is used to control the switching timing of the current direction switching module; at the same time, it receives the voltage V1 and voltage V2, and calculates the resistance value of the device under test based on the absolute value of the forward constant current or the reverse constant current, combined with the difference between voltage V1 and voltage V2.

2. The DC micro-resistance measuring device resistant to thermoelectric potential interference according to claim 1, characterized in that, The bidirectional programmable constant current source module includes a reference constant current source, a resistor R1, a voltage inverter U1, and an operational amplifier U3. The reference constant current source generates a positive reference voltage through R1, and the voltage inverter U1 converts the positive reference voltage into a reverse reference voltage. The operational amplifier U3 is used to condition the reference voltage and provide an input signal for subsequent current amplification.

3. The DC micro-resistance measuring device resistant to thermoelectric potential interference according to claim 2, characterized in that, The current direction switching module includes a three-channel single-pole double-throw analog switch U2. The input terminals of the analog switch U2 are connected to the forward reference voltage, the reverse reference voltage, and the 0V voltage, respectively. The output terminal of the analog switch U2 is connected to the non-inverting input terminal of the operational amplifier U3. By controlling the control terminal BA of the analog switch U2, the switching between forward current, reverse current, and stop is realized.

4. The DC micro-resistance measuring device resistant to thermoelectric potential interference according to claim 2, characterized in that, The bidirectional programmable constant current source module also includes a current amplification circuit, which includes a current-limiting resistor R4, a current-limiting resistor R5, a negative feedback capacitor C9, and a transistor amplification unit. The transistor amplification unit includes transistors Q1-Q4. Transistor Q1 drives transistor Q2 to form a forward path, and transistor Q3 drives transistor Q4 to form a reverse path. The output terminal of operational amplifier U3 is connected in series with the base of transistor Q1 with a current-limiting resistor R4. One end of the negative feedback capacitor C9 is electrically connected to the inverting input terminal of operational amplifier U3, and the other end of the negative feedback capacitor C9 is connected in series with a current-limiting resistor R5 and then connected to the base of transistor Q3.

5. The DC micro-resistance measuring device resistant to thermoelectric potential interference according to claim 4, characterized in that, The current amplification circuit also includes a sampling resistor R2 and a resistor R3; the sampling resistor R2 is connected in series between the device under test and ground, and the voltage across the sampling resistor R2 is fed back to the inverting input of the operational amplifier U3 through the resistor R3, forming a deep negative feedback.

6. The DC micro-resistance measuring device resistant to thermoelectric potential interference according to claim 4, characterized in that, Transistors Q1 and Q2 are NPN transistors, while transistors Q3 and Q4 are PNP transistors.

7. The DC micro-resistance measuring device resistant to thermoelectric potential interference according to claim 1, characterized in that, The voltage sampling module includes an analog switch U7, an operational amplifier U4, an operational amplifier U5, and an ADC module U8. The analog switch U7 is used to switch the sampling of one end SENSE+ and the other end SENSE- of the device under test. The operational amplifiers U4 and U5 are used to track and condition the sampled voltage. The ADC module U8 is used to convert the conditioned analog voltage into a digital signal, and a +2.5V bias voltage is superimposed on the input of the ADC module U8.

8. The DC micro-resistance measuring device resistant to thermoelectric potential interference according to claim 7, characterized in that, The differential input voltage of the ADC module U8 is 0.9 times the conditioned voltage. The ADC module U8 transmits digital signals to the signal processing module through the SPI interface.

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