Low resistance measuring instrument

Abstract

The utility model provides a low resistance measuring instrument, which relates to the technical field of resistance measurement and comprises a transformer, a rectifying circuit, a direct current ammeter, a direct current voltmeter, a positive voltage stabilizer, a three-terminal adjustable voltage stabilizer, an adjustable resistor and a Kelvin sampling clamp. According to the utility model, a constant current source with constant output current is formed by the three-terminal adjustable voltage stabilizer, the high-precision low-temperature drift resistor and the like, so that the voltage drop at the two ends of the element to be measured is more obvious. A four-wire method is adopted for detection, errors of contact resistance, lead resistance and the like can be effectively eliminated, interference caused by factors such as electromagnetic coupling between circuits and the like is reduced, the measurement result is more stable and reliable, and therefore the measurement precision is improved; and the structure is simple, manufacturing is easy, and manufacturing cost is low.

Description

Technical Field

[0001] This utility model relates to the field of resistance measurement technology, specifically to a low resistance measuring instrument. Background Technology

[0002] Currently, when it is necessary to obtain the winding resistance of large motors, transformers, reactors, etc., to test the contact resistance of electrical components such as switches, plugs, and sockets, and the resistance of precision power electronic components, a multimeter is generally used for measurement. However, because the resolution of ordinary multimeters is too low, the measured results within the range are not accurate enough, and therefore, it is impossible to measure the accurate resistance value. Utility Model Content

[0003] The purpose of this invention is to provide a low resistance measuring instrument to solve the problem that existing instruments cannot accurately measure the resistance value of the component under test. The measurement results are stable and reliable with high accuracy, thus enabling accurate measurement of the resistance value of the component under test.

[0004] To achieve the above objectives, this utility model provides a low resistance measuring instrument, including a transformer, a rectifier circuit, a DC ammeter, a DC voltmeter, a positive voltage regulator, a three-terminal adjustable voltage regulator, an adjustable resistor, and a Kelvin sampling clip.

[0005] The output terminal of the transformer is connected to the input terminal of the rectifier circuit. The first output terminal of the rectifier circuit is connected to the input terminal of the positive voltage regulator and the first terminal of the three-terminal adjustable voltage regulator. The output terminal of the positive voltage regulator is connected to a DC ammeter and a DC voltmeter. The second terminal of the three-terminal adjustable voltage regulator is connected to the first terminal of the adjustable resistor. The second terminal of the adjustable resistor is connected to the third terminal of the three-terminal adjustable voltage regulator. The third terminal of the three-terminal adjustable voltage regulator is connected to the first terminal of the Kelvin sampling clip via the DC ammeter. The second terminal of the Kelvin sampling clip is connected to the second output terminal of the rectifier circuit. The second and third terminals of the Kelvin sampling clip are connected to the DC voltmeter. The first and second terminals of the Kelvin sampling clip are connected to the first terminal of the device under test. The third and fourth terminals of the Kelvin sampling clip are connected to the second terminal of the device under test.

[0006] According to the low resistance measuring instrument provided by this utility model, the rectifier circuit is a rectifier bridge, and the rectifier bridge includes four diodes D8, D9, D10, and D11.

[0007] According to the low resistance measuring instrument provided by this utility model, a filter capacitor is connected between the first output terminal and the second output terminal of the rectifier circuit.

[0008] According to the low resistance measuring instrument provided by this utility model, the positive voltage regulator is model LM7812CT.

[0009] According to the low resistance measuring instrument provided by this utility model, the model of the three-terminal adjustable voltage regulator is LM317AH.

[0010] According to the present invention, a low resistance measuring instrument is provided, wherein the adjustable resistor includes a resistor R1, a fixed resistor R2 and a fixed resistor R3, the resistance value of the resistor R1 is adjustable, and the resistor R1 and the fixed resistor R3 are connected in series and then connected in parallel with the fixed resistor R2.

[0011] According to the low resistance measuring instrument provided by this utility model, the second end of the Kelvin sampling clip is connected to the second output end of the rectifier circuit via diode D5.

[0012] According to the low resistance measuring instrument provided by this utility model, the two ends of the diode D5 are connected to a Zener diode D1.

[0013] According to the low resistance measuring instrument provided by this utility model, a diode D4 is connected between the first end of the three-terminal adjustable voltage regulator and the second end of the Kelvin sampling clip.

[0014] According to the low resistance measuring instrument provided by this utility model, the DC ammeter is a four-and-a-half-digit DC ammeter, and the DC voltmeter is a four-and-a-half-digit DC voltmeter.

[0015] The technical solution of this utility model has at least the following technical effects:

[0016] This invention provides a low-resistance measuring instrument, comprising a transformer, a rectifier circuit, a DC ammeter, a DC voltmeter, a positive voltage regulator, a three-terminal adjustable voltage regulator, an adjustable resistor, and a Kelvin sampling clip. This invention uses a three-terminal adjustable voltage regulator and a high-precision, low-temperature drift resistor to form a constant current source with a constant output current, making the voltage drop across the measured component more significant. It employs a four-wire method for detection, effectively eliminating errors caused by contact resistance and lead resistance, and reducing interference from factors such as electromagnetic coupling between lines, resulting in more stable and reliable measurement results, thereby improving measurement accuracy. Furthermore, it has a simple structure, is easy to manufacture, and has low cost. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this utility model. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] In the attached diagram:

[0019] Figure 1 This is a circuit diagram of the low resistance measuring instrument of this utility model;

[0020] Figure 2 for Figure 1 The enlarged view at point I shows the specific details of the Kelvin sampling clip. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this utility model clearer, the technical solutions of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this utility model.

[0022] The following description, in conjunction with the accompanying drawings, details some embodiments of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0023] Please see Figure 1 This utility model provides a low resistance measuring instrument, including a transformer, a rectifier circuit, a DC ammeter, a DC voltmeter, a positive voltage regulator, a three-terminal adjustable voltage regulator, an adjustable resistor, and a Kelvin sampling clip;

[0024] The output terminal of the transformer is connected to the input terminal of the rectifier circuit. The first output terminal of the rectifier circuit is connected to the input terminal of the positive voltage regulator and the first terminal of the three-terminal adjustable voltage regulator. The output terminal of the positive voltage regulator is connected to a DC ammeter and a DC voltmeter. The second terminal of the three-terminal adjustable voltage regulator is connected to the first terminal of the adjustable resistor. The second terminal of the adjustable resistor is connected to the third terminal of the three-terminal adjustable voltage regulator. The third terminal of the three-terminal adjustable voltage regulator is connected to the first terminal of the Kelvin sampling clip via the DC ammeter. The second terminal of the Kelvin sampling clip is connected to the second output terminal of the rectifier circuit. The second and third terminals of the Kelvin sampling clip are connected to the DC voltmeter. The first and second terminals of the Kelvin sampling clip are connected to the first terminal of the device under test. The third and fourth terminals of the Kelvin sampling clip are connected to the second terminal of the device under test.

[0025] It should be noted that, as Figure 2 As shown, the Kelvin sampling clip includes clip A and clip B. The blue part is the insulated handle. The left and right jaws of clip A are the second and first ends of the Kelvin sampling clip, respectively. The left and right jaws of clip B are the third and fourth ends of the Kelvin sampling clip, respectively.

[0026] The overall circuit structure of this utility model can be divided into the following parts:

[0027] Power supply section

[0028] V1 (AC power supply): Provides a 220Vrms (Root Mean Square) 50Hz AC voltage, which serves as the initial power input for the circuit and provides the basis for subsequent transformation, rectification and other operations.

[0029] T1 (Transformer, Model 220V / 12V 20W): Steps down the 220V AC voltage at a transformation ratio of 10:0.4, converting the high voltage into a low voltage suitable for subsequent circuit processing, thereby reducing the voltage to ensure the safe and stable operation of the subsequent circuits.

[0030] Rectifier and filter section

[0031] The rectifier circuit can be a rectifier bridge, which includes four diodes D8, D9, D10, and D11 (diodes, model 1N5404 3A 400V) to convert the AC voltage stepped down by the transformer into DC voltage. Utilizing the unidirectional conductivity of the diodes, they conduct during the positive and negative half-cycles of the AC voltage, resulting in a unidirectional pulsating DC voltage output.

[0032] A filter capacitor C2 (2400uf 50V) is connected between the first and second output terminals of the rectifier circuit. The capacitor C2 works with the rectifier bridge to filter the voltage. The capacitance is selected according to the formula C=IMAX / F*U, which can control the ripple voltage to 0.5V. Here, IMAX represents the maximum current value of the load connected to the rectifier circuit, F represents the frequency of the rectified DC ripple voltage, and U represents the ripple voltage present in the rectified DC ripple voltage. This parameter directly affects the stability of the DC voltage.

[0033] Voltage stabilization section

[0034] The positive voltage regulator U4 can be model LM7812CT. It stabilizes the input voltage at a 12V output and powers the DC ammeter U2 and DC voltmeter U3.

[0035] The three-terminal adjustable voltage regulator can be model LM317AH, where the voltage U between the Vout terminal and the ADJ terminal is... AB Basically, it remains unchanged at 1.25V, such as Figure 1 As shown, the output current I1 at the Vout terminal is equal to the current I2 flowing into the DC ammeter U2, and satisfies:

[0036] I1=I2=U AB / ((R1+R3)*R2 / (R1+R2+R3)).

[0037] Constant current source and measurement section

[0038] The adjustable resistors include resistor R1, fixed resistors R2 and R3. The resistance of R1 is adjustable. R1 and R3 are connected in series and then in parallel with fixed resistor R2. The maximum resistance of R1 is 50Ω. Fixed resistor R2 is a high-precision, low-temperature-drift 3W resistor with a resistance of 1.3Ω. Fixed resistor R3 is also a high-precision, low-temperature-drift 3W resistor with a resistance of 15Ω. Together with a three-terminal adjustable voltage regulator, they form part of a constant current source circuit. By adjusting the resistance value of R1 and combining it with the output voltage of the three-terminal adjustable voltage regulator, the constant current value in the constant current source circuit is determined. Because the adjustable resistors have relatively low power, R1, R2, and R3 are connected in parallel.

[0039] The DC ammeter U2 is a four-and-a-half-digit DC ammeter used to measure the DC current value in a circuit and display the current current passing through the component under test.

[0040] The DC voltmeter U3 is a 4.5-digit DC voltmeter used to measure the voltage across the components under test. According to Ohm's law R = U / I, the resistance of the component can be calculated. If the current output is adjusted to 1A, the value displayed on the DC voltmeter is the resistance of the component.

[0041] The second end of the Kelvin sampling clip is connected to the second output terminal of the rectifier circuit via diode D5, which is model 1N4007. After the measurement is completed, when the Kelvin sampling clip is released, it can provide a circuit for the inductor to discharge.

[0042] A Zener diode D1 is connected across diode D5. Diode D1 is a 1N4728A, a 3.3V Zener diode that can protect the DC voltmeter from exceeding its maximum range of 3.5V.

[0043] A diode D4, model 1N4007, is connected between the first terminal of the three-terminal adjustable voltage regulator and the second terminal of the Kelvin sampling clip. This diode acts as a protection device when there is external power generation.

[0044] The component under test (RL) is the component whose resistance needs to be measured, such as the resistor under test. When current flows through it, its resistance value is obtained by measuring the voltage across its terminals.

[0045] It should be noted that this invention utilizes a constant current source and a four-wire method for resistance measurement. The constant current source provides a stable and accurate constant current. The four-wire method samples the voltage of the component under test, processes it using an analog-to-digital converter, and displays the measurement result on a 4.5-digit voltmeter. Based on Ohm's law R=U / I, the resistance value of the component under test can be accurately determined.

[0046] The working principle of this utility model is as follows:

[0047] 1. Formation of a constant current source:

[0048] The AC power supply V1 (AC 220V, 50Hz) is connected to transformer T1 and the voltage is reduced to AC12V. After rectification and filtering by the rectifier circuit, DC12V is sent to the LM317 voltage regulator. By adjusting the adjustable resistor R1, the LM317 voltage regulator outputs a constant current of 1A and a voltage of 1.25V.

[0049] 2. Measurement circuit:

[0050] The LM317AH outputs a constant 1A current from its ADJ pin. This current passes through a DC ammeter U2 and is then connected to the first terminal of a Kelvin sampling clip. The current flows through the resistor under test and forms a loop through the fourth terminal of the Kelvin sampling clip. The positive terminal of a DC voltmeter is connected to the second terminal of the Kelvin sampling clip, and the negative terminal is connected to the third terminal, thus detecting the voltage across the resistor under test.

[0051] Adjust the resistance of resistor R1 to stabilize the current output at 1A. Diodes D1, D4, and D5 provide back EMF protection for the circuit. The LM7812CT provides the operating power for the DC voltmeter and DC ammeter.

[0052] 3. Instructions for use:

[0053] The measuring range of this low resistance measuring instrument is 0.0001-3.3Ω.

[0054] Confirm that the component under test is in a power-off state.

[0055] When a 220V AC power supply is applied to the low resistance meter, the DC voltmeter U3 displays "HHHHH" and the DC ammeter U2 displays 0.0497-0.0500. Shorting the Kelvin sampling clip, the DC voltmeter U3 displays "00000", indicating that the low resistance meter has returned to zero normally. Adjusting the resistance of resistor R1 adjusts the output current to 1A, resulting in a constant current output of 1A.

[0056] Attach the Kelvin sampling clip to the component under test, ensuring a secure connection and good contact. The reading on DC voltmeter U3 will then represent the resistance value. For example, if DC voltmeter U3 displays "0.0500", the resistance of the component under test is 0.05Ω. If DC voltmeter U3 displays "HHHHH", it indicates that the resistance of the component under test is greater than 3.3Ω, and the low-resistance measuring instrument cannot measure it.

[0057] During long-term use of the low resistance measuring instrument, the heating of the components has a slight impact on the current. The resistance value of resistor R1 can be adjusted to adjust the output current to 1A.

[0058] The following is a specific embodiment of this utility model.

[0059] The low resistance measuring instrument of this invention and the ZGY-10 DC resistance tester were used to measure the precision resistance. The resistance values ​​of the precision resistors to be measured were 0.1Ω, 0.02Ω, 0.05Ω, and 0.005Ω. The measurements were performed using the low resistance measuring instrument of this invention and the ZGY-10 DC resistance tester, and the measured values ​​were recorded. The results are shown in Table 1.

[0060] Table 1. Measurement Results

[0061]

[0062] As can be seen from the analysis of Table 1, there is a certain degree of operational error in the measurement results, which is quite common in actual measurements and is usually considered normal. Furthermore, the low-resistance measuring instrument of this invention has high measurement accuracy and can accurately measure the resistance value of the resistor to be measured.

[0063] In summary, the low resistance measuring instrument provided by this utility model has the following advantages:

[0064] 1. Simple structure, easy to manufacture, and low cost.

[0065] 2. A constant current source with an output current of 1A is formed by a three-terminal adjustable voltage regulator and a high-precision low-temperature drift resistor, making the voltage drop across the component under test more significant. The four-wire method is used for detection, which effectively eliminates errors caused by contact resistance, lead resistance, etc., and reduces interference caused by factors such as electromagnetic coupling between lines, making the measurement results more stable and reliable, thereby improving measurement accuracy.

[0066] 3. It adopts a four-and-a-half-digit digital ammeter and voltmeter reading, with a measurement range from 0.0001Ω to 3.3Ω, which can meet the measurement needs of different low resistances.

[0067] 4. It has a fast response time and can provide accurate measurement results in a short time, improving measurement efficiency.

[0068] 5. The measurement process is very simple. Just clip the Kelvin sampling clip to both ends of the component under test, and the low resistance meter can quickly and accurately display the measurement results. The whole process requires no complicated operating steps, and even first-time users can easily get started.

[0069] 6. It has a back EMF protection function to prevent damage to the instrument due to back EMF when the Kelvin sampling clip is disconnected from the device under test or when there is poor contact.

[0070] Other embodiments of the present invention will readily occur to those skilled in the art upon consideration of the specification and practice of the embodiments disclosed herein. The present invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. It should be understood that the present invention is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the present invention is limited only by the appended claims.

Claims

1. A low resistance measuring instrument, characterized by, This includes transformers, rectifier circuits, DC ammeters, DC voltmeters, positive voltage regulators, three-terminal adjustable voltage regulators, adjustable resistors, and Kelvin sampling clips; The output terminal of the transformer is connected to the input terminal of the rectifier circuit. The first output terminal of the rectifier circuit is connected to the input terminal of the positive voltage regulator and the first terminal of the three-terminal adjustable voltage regulator. The output terminal of the positive voltage regulator is connected to a DC ammeter and a DC voltmeter. The second terminal of the three-terminal adjustable voltage regulator is connected to the first terminal of the adjustable resistor. The second terminal of the adjustable resistor is connected to the third terminal of the three-terminal adjustable voltage regulator. The third terminal of the three-terminal adjustable voltage regulator is connected to the first terminal of the Kelvin sampling clip via the DC ammeter. The second terminal of the Kelvin sampling clip is connected to the second output terminal of the rectifier circuit. The second and third terminals of the Kelvin sampling clip are connected to the DC voltmeter. The first and second terminals of the Kelvin sampling clip are connected to the first terminal of the device under test. The third and fourth terminals of the Kelvin sampling clip are connected to the second terminal of the device under test.

2. The low resistance measuring instrument of claim 1, wherein, The rectifier circuit is a rectifier bridge, which includes four diodes D8, D9, D10, and D11.

3. The low resistance measuring instrument of claim 1, wherein, A filter capacitor is connected between the first output terminal and the second output terminal of the rectifier circuit.

4. The low resistance measuring instrument of claim 1, wherein, The positive voltage regulator is model LM7812CT.

5. The low resistance measuring instrument of claim 1, wherein, The model of the three-terminal adjustable voltage regulator is LM317AH.

6. The low resistance measuring instrument of claim 1, wherein, The adjustable resistor includes resistor R1, fixed resistor R2 and fixed resistor R3. The resistance value of resistor R1 is adjustable. Resistor R1 and fixed resistor R3 are connected in series and then connected in parallel with fixed resistor R2.

7. The low resistance measuring instrument of claim 1, wherein, The second end of the Kelvin sampling clip is connected to the second output end of the rectifier circuit via diode D5.

8. The low resistance measuring instrument of claim 7, wherein, A Zener diode D1 is connected to both ends of the diode D5.

9. The low resistance measuring instrument of claim 8, wherein, A diode D4 is connected between the first terminal of the three-terminal adjustable voltage regulator and the second terminal of the Kelvin sampling clip.

10. The low resistance measuring instrument of claim 1, wherein, The DC ammeter is a four-and-a-half-digit DC ammeter, and the DC voltmeter is a four-and-a-half-digit DC voltmeter.

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