Micro-resistance measuring circuit

Abstract

The utility model relates to a micro-resistance measuring circuit, which comprises a constant current source, a standard resistor, a measured resistor, an amplifying circuit, a micro-processing unit and a display. The output end of the constant current source is connected with one end of the standard resistor and the input end of the microprocessing unit, the other end of the standard resistor is connected with the microprocessing unit, the tested resistor and the input end of the amplifying circuit, the other end of the tested resistor is connected with the amplifying circuit and the input end of the constant current source, and the output end of the amplifying circuit is connected with the microprocessing unit. The micro-processing unit is in output connection with the display. The standard resistor generates a first voltage difference, the measured resistor generates a second voltage difference, the amplifying circuit amplifies the second voltage difference, and the microprocessing unit converts an analog signal into a digital signal and controls and displays a measurement result. Measurement results only depend on standard resistance precision, current fluctuation of the constant current source can be completely offset, and measurement stability is remarkably improved.

Description

TECHNICAL FIELD

[0001] The utility model relates to a kind of micro-resistance measurement circuits, belong to resistance measurement technical field. BACKGROUND

[0002] In the field of resistance measurement, especially in the accurate measurement of micro-ohm resistance (such as circuit board on-resistance, battery internal resistance, contact resistance, etc.), the traditional method usually relies on the principle of constant current source excitation combined with voltage detection. The typical scheme applies a stable current to the measured resistance by a constant current source, measures the voltage difference across it, and calculates the resistance value according to Ohm's law. However, such methods have the following limitations in practical applications: the accuracy of the traditional measurement circuit is directly limited by the output current stability of the constant current source. Since the current of the constant current source is easily affected by factors such as temperature drift, power supply fluctuation or component aging, the voltage signal of the measured resistance is deviated, especially in micro-resistance measurement, small current fluctuations are significantly amplified, which seriously affects the repeatability of the measurement results. The voltage signal generated by the micro-resistance is usually in the order of microvolts to millivolts, which is easily affected by environmental electromagnetic noise, common-mode interference or amplifier offset voltage. In the prior art, simple single-ended amplification circuits cannot effectively suppress noise, resulting in a decrease in signal-to-noise ratio and limited measurement resolution. SUMMARY

[0003] To solve the problems existing in the prior art, the utility model provides a micro-resistance measurement circuit.

[0004] The technical solution of the utility model is as follows:

[0005] A micro-resistance measurement circuit, comprising a constant current source, a standard resistance, a measured resistance, an amplification circuit, a micro-processing unit and a display;

[0006] The power input end of the constant current source and the power input end of the micro-processing unit are connected to a power supply, the output end of the constant current source is connected to one end of the standard resistance and the input end of the micro-processing unit, the other end of the standard resistance is connected to the input end of the micro-processing unit, one end of the measured resistance and the input end of the amplification circuit, the other end of the measured resistance is connected to the input end of the amplification circuit and the input end of the constant current source, the output end of the amplification circuit is connected to the input end of the micro-processing unit, and the output end of the micro-processing unit is connected to the input end of the display;

[0007] The amplification circuit is used to amplify the input voltage difference;

[0008] The micro-processing unit is used to convert the analog signal of the input voltage difference into a digital signal and control the display to display the micro-resistance measurement result.

[0009] As a preferred embodiment of the utility model, the constant current source comprises a first amplifier, a voltage stabilizing diode and a first triode;

[0010] The positive electrode of the voltage stabilizing diode and one end of the second resistor are connected to a power supply, the negative electrode of the voltage stabilizing diode is connected to ground through the first resistor, and is connected to the same direction input end of the first amplifier;

[0011] The other end of the second resistor is connected to the opposite direction input end of the first amplifier and the emitter of the first triode, the output end of the first amplifier is connected to the base of the first triode, and the collector of the first triode is connected to one end of the standard resistor and the micro processing unit.

[0012] As a preferred embodiment of the utility model, the amplification circuit comprises a second amplifier;

[0013] The other end of the standard resistor is connected to one end of a third resistor, and the other end of the measured resistor is connected to one end of a fifth resistor and to ground;

[0014] The other end of the third resistor is connected to one end of a fourth resistor and the same direction input end of the second amplifier, the other end of the fifth resistor is connected to one end of a sixth resistor and the opposite direction input end of the second amplifier, and the other end of the fourth resistor, the other end of the sixth resistor and the output end of the second amplifier are connected to the micro processing unit.

[0015] As a preferred embodiment of the utility model, the micro processing unit comprises a micro processor;

[0016] One end of an eighth resistor is connected to the collector of the first triode, the other end of the eighth resistor is connected to the positive reference voltage end of the micro processor and one end of a first capacitor, and the other end of the standard resistor and the other end of the first capacitor are connected to the negative reference voltage end of the micro processor;

[0017] The first RC oscillation end of the micro processor is connected to one end of a ninth resistor and one end of a third capacitor, the other end of the ninth resistor is connected to the second RC oscillation end of the micro processor, and the other end of the third capacitor is connected to the third RC oscillation end of the micro processor;

[0018] The positive reference capacitor end of the micro processor is connected to the negative reference capacitor end of the micro processor through a fourth capacitor;

[0019] The other end of the fourth resistor is connected to the analog signal common end of the micro processor and the negative signal input end of the micro processor and to ground;

[0020] The other end of the sixth resistor and the output end of the second amplifier are connected to one end of a seventh resistor, the other end of the seventh resistor is connected to the positive signal input end of the micro processor and to the negative signal input end of the micro processor through a second capacitor;

[0021] The automatic zeroing capacitor end of the microprocessor is connected with one end of the tenth resistor and one end of the sixth capacitor through the fifth capacitor, the other end of the tenth resistor is connected with the integral resistor end of the microprocessor, and the other end of the sixth capacitor is connected with the integral capacitor end of the microprocessor.

[0022] The power positive end of the microprocessor is connected with the power positive pole, and the power negative end of the microprocessor is connected with the power negative pole.

[0023] As the preferred embodiment of the utility model, the first liquid crystal display driving end and the second liquid crystal display driving end of the microprocessor are connected with the stroke end of the display.

[0024] The utility model has the advantages of the following:

[0025] The utility model measures the result only in the precision of standard resistance Ro, and the fluctuation of constant current source current Io is completely offset, and the measurement stability is obviously improved. The double integral type analog-digital converter (such as 7106 chip) is adopted, the integral resistance and the capacitor are combined, the high-precision conversion of microvolt level signal is realized, and the utility model is suitable for micro-ohm resistance measurement. The differential structure is constructed by using operational amplifier (A2) in the amplification circuit, and common-mode noise (such as environmental electromagnetic interference) is effectively suppressed. The output current of the constant current source is little affected by power fluctuation through the closed-loop feedback design of operational amplifier (A1) and triode (Q1). BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is the module connection diagram of the utility model.

[0027] Figure 2 It is the circuit connection diagram of the utility model. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the utility model will be clearly and completely described below with reference to the drawings in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, rather than all the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the utility model.

[0029] It should be understood that the step numbers used in the description are only for the convenience of description, and are not limited to the execution sequence of the steps.

[0030] It should be understood that the terms used in the description of the utility model are only for the purpose of describing specific embodiments and are not intended to limit the utility model. As used in the description and the appended claims of the utility model, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include the plural forms.

[0031] The terms "comprise" and "comprising" mean that the described features, integers, steps, operations, elements, and / or components are present, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0032] The term "and / or" means any combination of one or more of the associated listed items and all possible combinations thereof.

[0033] Embodiment One:

[0034] In this embodiment, the microprocessor is Figure 2 U1 shown in the figure, model 7106, the first liquid crystal display drive end of the microprocessor is Figure 2 the D1 port of U1 shown in the figure, the second liquid crystal display drive end of the microprocessor is Figure 2 the LBT port of U1 shown in the figure, the positive power supply end of the microprocessor is Figure 2 the V+ port of U1 shown in the figure, the negative power supply end of the microprocessor is Figure 2 the V- port of U1 shown in the figure, the first RC oscillation end of the microprocessor is Figure 2 the OSC1 port of U1 shown in the figure, the second RC oscillation end of the microprocessor is Figure 2 the OSC2 port of U1 shown in the figure, the third RC oscillation end of the microprocessor is Figure 2 the OSC3 port of U1 shown in the figure, the positive reference voltage end of the microprocessor is Figure 2 the R+ port of U1 shown in the figure, the negative reference voltage end of the microprocessor is Figure 2 the R- port of U1 shown in the figure, the positive reference capacitor end of the microprocessor is Figure 2 the Cref+ port of U1 shown in the figure, the negative reference capacitor end of the microprocessor is Figure 2 the Cref- port of U1 shown in the figure, the analog signal common end of the microprocessor is Figure 2 the COM port of U1 shown in the figure, the negative signal input end of the microprocessor is Figure 2 the IN- port of U1 shown in the figure, the positive signal input end of the microprocessor is Figure 2 the IN+ port of U1 shown in the figure, the negative signal input end of the microprocessor is Figure 2 the IN- port of U1 shown in the figure, the auto-zero capacitor end of the microprocessor is Figure 2 the Caz port of U1 shown in the figure, the integration resistance end of the microprocessor is Figure 2 the BUF port of U1 shown in the figure, the integration capacitor end of the microprocessor is Figure 2 the INF port of U1 shown in the figure;

[0035] The display is Figure 2 the LCD shown in the figure;

[0036] The voltage stabilizing diode isFigure 2 The first resistor of DZ1 shown is Figure 2 R1 is shown, and the second resistor is Figure 2 R2 shown, the first amplifier is Figure 2 As shown in Figure A1, the first transistor is... Figure 2 The third resistor in Q1 shown is Figure 2 R3 shown, the fourth resistor is Figure 2 R4 shown, the fifth resistor is Figure 2 R5 shown, the sixth resistor is Figure 2 R6 shown is the second amplifier. Figure 2 As shown in Figure A2, the seventh resistor is Figure 2 R7 shown is the eighth resistor. Figure 2 R8 shown, the ninth resistor is Figure 2 R9 shown, the tenth resistor is Figure 2 R10 shown, the first capacitor is Figure 2 C1 is shown, and the second capacitor is... Figure 2 C2 shown is the third capacitor. Figure 2 As shown in the figure, C3 is the fourth capacitor. Figure 2 C4, the fifth capacitor shown, is Figure 2 C5, the sixth capacitor shown, is Figure 2 C6 as shown;

[0037] Standard resistor is Figure 2 The resistance of Ro shown is the resistance to be measured. Figure 2 The first voltage difference of Rx shown is Figure 2 The Vo shown is the second voltage difference. Figure 1-2 The constant current source output current shown is Vx. ​ The Io shown;

[0038] Vo = Io * Ro;

[0039] Vx = Io * Rx;

[0040] See ​ A micro-resistance measurement circuit includes a constant current source, a standard resistor, a resistor to be measured, an amplifier circuit, a microprocessor unit, and a display.

[0041] The power input terminal of the constant current source and the power input terminal of the microprocessor unit are connected to a power source. The output terminal of the constant current source is connected to one end of a standard resistor and the input terminal of the microprocessor unit. The other end of the standard resistor is connected to the input terminal of the microprocessor unit, one end of the resistor under test, and the input terminal of the amplifier circuit. The other end of the resistor under test is connected to the input terminal of the amplifier circuit and the input terminal of the constant current source. The output terminal of the amplifier circuit is connected to the input terminal of the microprocessor unit. The output terminal of the microprocessor unit is connected to the input terminal of the display.

[0042] the standard resistance is used to generate a first voltage difference;

[0043] the measured resistance is used to generate a second voltage difference;

[0044] the amplification circuit is used to amplify the second voltage difference to obtain an amplified voltage difference;

[0045] the micro-processing unit is used to convert analog signals of the first voltage difference and the amplified voltage difference into digital signals, and control the display to display a micro-resistance measurement result, the micro-resistance measurement result being a ratio of the first voltage difference and the amplified voltage difference.

[0046] As a preferred embodiment of the utility model, the constant current source comprises a first amplifier, a stabilizing diode and a first triode;

[0047] the anode of the stabilizing diode and one end of a second resistance are connected to a power supply, the cathode of the stabilizing diode is connected to ground through a first resistance and connected to a same direction input end of the first amplifier respectively;

[0048] the other end of the second resistance is connected to an opposite direction input end of the first amplifier and an emitter of the first triode respectively, an output end of the first amplifier is connected to a base of the first triode, and a collector of the first triode is connected to one end of a standard resistance and a micro-processing unit respectively.

[0049] As a preferred embodiment of the utility model, the amplification circuit comprises a second amplifier;

[0050] the other end of the standard resistance is connected to one end of a third resistance, and the other end of the measured resistance is connected to one end of a fifth resistance and to ground respectively;

[0051] the other end of the third resistance is connected to one end of a fourth resistance and a same direction input end of the second amplifier respectively, the other end of the fifth resistance is connected to one end of a sixth resistance and an opposite direction input end of the second amplifier respectively, and the other end of the fourth resistance, the other end of the sixth resistance and an output end of the second amplifier are connected to the micro-processing unit.

[0052] As a preferred embodiment of the utility model, the micro-processing unit comprises a microprocessor;

[0053] one end of an eighth resistance is connected to the collector of the first triode, the other end of the eighth resistance is connected to a positive reference voltage end of the microprocessor and one end of a first capacitor respectively, and the other end of the standard resistance and the other end of the first capacitor are connected to a negative reference voltage end of the microprocessor;

[0054] The first RC oscillation end of the microprocessor is connected with one end of the ninth resistor and one end of the third capacitor respectively, the other end of the ninth resistor is connected with the second RC oscillation end of the microprocessor, and the other end of the third capacitor is connected with the third RC oscillation end of the microprocessor;

[0055] The reference capacitor positive end of the microprocessor is connected with the reference capacitor negative end of the microprocessor through the fourth capacitor;

[0056] The other end of the fourth resistor is connected with the analog signal common end of the microprocessor and the signal input negative end of the microprocessor respectively, and is grounded;

[0057] The other end of the sixth resistor and the output end of the second amplifier are connected with one end of the seventh resistor, the other end of the seventh resistor is connected with the signal input positive end of the microprocessor respectively, and is connected with the signal input negative end of the microprocessor through the second capacitor;

[0058] The auto-zero capacitor end of the microprocessor is connected with one end of the tenth resistor and one end of the sixth capacitor through the fifth capacitor respectively, the other end of the tenth resistor is connected with the integral resistor end of the microprocessor, and the other end of the sixth capacitor is connected with the integral capacitor end of the microprocessor;

[0059] The positive electrode end of the microprocessor is connected with the positive electrode of the power supply, and the negative electrode end of the microprocessor is connected with the negative electrode of the power supply.

[0060] As the preferred embodiment of the utility model, the first liquid crystal display driving end and the second liquid crystal display driving end of the microprocessor are connected with the stroke end of the display.

[0061] The measurement principle is explained as follows:

[0062] The second voltage difference Vx is amplified by the second amplifier, and an amplified voltage difference Vin is outputted:

[0063] Vin=A*Io*Rx;

[0064] Wherein, A represents the amplification ratio;

[0065] The micro-resistance measurement result N is represented as:

[0066] N=Vin / Vo

[0067] =(A*Io*Rx) / (Io*Ro)

[0068] =(A / Ro)*Rx;

[0069] Since the standard resistance Ro and the amplification ratio A have fixed values in the circuit work, A / R0=1 is set, that is, N=Rx, and the resistance value of the measured resistance Rx is realized by the standard resistance Ro and the amplification circuit, which is not affected by the precision and stability of the constant current source current, but is only affected by the precision and stability of the standard resistance Ro.

[0070] The constant current source is closed-loop controlled by the voltage stabilizing diode, the first amplifier A1 and the first triode Q1, and outputs a stable current Io. The current flows through the standard resistor Ro and the measured resistor Rx, and generates a first voltage difference Vo and a second voltage difference Vx, respectively;

[0071] The stability of the constant current source directly affects the accuracy of Vo and Vx, but the current Io will be eliminated in subsequent calculations, so the final result only depends on the accuracy of the standard resistor Ro.

[0072] Analog-to-digital conversion: a double integration type ADC (such as 7106 chip) is used to convert analog voltage into high-precision digital signal through integration, comparison and zeroing phase.

[0073] Anti-interference design:

[0074] Automatic zeroing: the offset voltage of the operational amplifier is eliminated by the capacitor (Caz).

[0075] Integral element: the integral resistor (R10) and the integral capacitor (C6) are used to smooth the signal and suppress high-frequency noise.

[0076] Reference capacitor (C4): provides a stable reference voltage to ensure the accuracy of ADC conversion.

[0077] In the embodiments of the present application, "at least one" means one or more, and "multiple" means two or more. The association relationship between the associated objects is described by "and / or", which means that there can be three kinds of relationships, for example, A and / or B, which can represent the existence of A alone, the existence of A and B together, and the existence of B alone. Wherein A, B can be singular or plural. The character " / " generally represents an "or" relationship between the associated objects before and after it. "At least one of the following" and the like means any combination of these items, including any combination of single or multiple 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, wherein a, b, c can be single or multiple.

[0078] The above description is only an embodiment of the present application, and does not limit the patent range of the present application. Any equivalent structure or equivalent process transformation using the content of the present application specification and drawings, or direct or indirect application in other related technical fields, is also included in the patent protection range of the present application.

Claims

1. A micro-ohmmeter circuit, comprising: The constant current source, the standard resistance, the measured resistance, the amplification circuit, the micro-processing unit and the display are included. The power input end of the constant current source and the power input end of the micro-processing unit are connected with a power supply, the output end of the constant current source is connected with one end of the standard resistance and the input end of the micro-processing unit respectively, the other end of the standard resistance is connected with the input end of the micro-processing unit, one end of the measured resistance and the input end of the amplification circuit respectively, the other end of the measured resistance is connected with the input end of the amplification circuit and the input end of the constant current source respectively, the output end of the amplification circuit is connected with the input end of the micro-processing unit, and the output end of the micro-processing unit is connected with the input end of the display. The amplification circuit is used for amplifying the input voltage difference. The micro-processing unit is used for converting the analog signal of the input voltage difference into a digital signal and controlling the display to display the micro-resistance measurement result.

2. The micro-ohmmeter circuit of claim 1, wherein, The constant current source includes a first amplifier, a voltage stabilizing diode and a first triode. The anode of the voltage stabilizing diode and one end of a second resistance are connected with a power supply, the cathode of the voltage stabilizing diode is connected with the ground through a first resistance and connected with the same direction input end of the first amplifier respectively. The other end of the second resistance is connected with the reverse direction input end of the first amplifier and the emitter of the first triode respectively, the output end of the first amplifier is connected with the base of the first triode, and the collector of the first triode is connected with one end of the standard resistance and the micro-processing unit.

3. The micro-ohmmeter circuit of claim 2, wherein, The amplification circuit includes a second amplifier. The other end of the standard resistance is connected with one end of a third resistance, and the other end of the measured resistance is connected with one end of a fifth resistance and the ground respectively. The other end of the third resistance is connected with one end of a fourth resistance and the same direction input end of the second amplifier respectively, the other end of the fifth resistance is connected with one end of a sixth resistance and the reverse direction input end of the second amplifier respectively, the other end of the fourth resistance, the other end of the sixth resistance and the output end of the second amplifier are connected with the micro-processing unit.

4. The micro-resistance measurement circuit of claim 3, wherein, The micro-processing unit includes a microprocessor. One end of an eighth resistance is connected with the collector of the first triode, the other end of the eighth resistance is connected with the positive reference voltage end of the microprocessor and one end of a first capacitor respectively, and the other end of the standard resistance and the other end of the first capacitor are connected with the negative reference voltage end of the microprocessor. The first RC oscillation end of the microprocessor is connected with one end of a ninth resistance and one end of a third capacitor respectively, the other end of the ninth resistance is connected with the second RC oscillation end of the microprocessor, and the other end of the third capacitor is connected with the third RC oscillation end of the microprocessor. The positive reference capacitor end of the microprocessor is connected with the negative reference capacitor end of the microprocessor through a fourth capacitor. The other end of the fourth resistance is connected with the analog signal common end of the microprocessor and the negative signal input end of the microprocessor respectively and grounded. The other end of the sixth resistance and the output end of the second amplifier are connected with one end of a seventh resistance, the other end of the seventh resistance is connected with the positive signal input end of the microprocessor respectively and connected with the negative signal input end of the microprocessor through a second capacitor. The automatic zeroing capacitor end of the microprocessor is connected with one end of the tenth resistor and one end of the sixth capacitor through the fifth capacitor, the other end of the tenth resistor is connected with the integral resistor end of the microprocessor, and the other end of the sixth capacitor is connected with the integral capacitor end of the microprocessor. The positive electrode end of the microprocessor is connected with the positive electrode of the power supply, and the negative electrode end of the microprocessor is connected with the negative electrode of the power supply.

5. The micro-ohmmeter circuit of claim 4, wherein, The first liquid crystal display driving end and the second liquid crystal display driving end of the microprocessor are connected with the stroke end of the display.

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