Circuit for inductance value measurement

Abstract

The utility model discloses a circuit for inductance value measurement, comprising a frequency circuit which comprises an oscillator, a variable capacitance diode, an adjustable resistor and a third resistor; a first fixed end of the adjustable resistor is connected with a preset voltage, a second fixed end of the adjustable resistor is grounded, an adjustable end of the adjustable resistor is connected with one end of the third resistor, and the other end of the third resistor is respectively connected with a positive electrode of the variable capacitance diode and a twelfth end of the oscillator; the tenth end and the twelfth end of the oscillator are used as access ends of a measured inductor, and the third end of the oscillator is used as a frequency signal output end; the frequency signal output end is connected with a frequency instrument to measure a frequency value, the frequency instrument is connected with a calculator, the calculator outputs and displays an inductance value by calculating the frequency value and a preset capacitance value, and the preset capacitance value is a capacitance value, adjusted by the adjustable resistor, of the variable capacitance diode. The inductance value measuring device is low in cost and accurate in measured inductance value.

Description

Technical Field

[0001] The utility model relates to the field of inductance measurement, in particular to a circuit for inductance measurement. Background Art

[0002] Inductor is a commonly used electronic component. It has basic functions such as filtering, oscillation, delay, notch, voltage leading current, and generating reactive power as an inductive load. Therefore, it is widely used in electronic circuits and industrial analog loads. Inductance is the most important parameter of inductance. Special inductance measuring instruments generally use bridge method (AC bridge), resonance method, digital measurement method and other methods. Most traditional inductance measurement methods have problems such as high cost, complex operation, and low measurement accuracy, which are difficult to meet the needs of practical applications. Therefore, it is of great practical value to develop a low-cost, high-precision inductance measurement circuit. Utility Model Content

[0003] In order to solve the above problems, the purpose of the utility model is to provide a circuit for measuring inductance, which has low cost and can measure accurate inductance.

[0004] Based on this, the utility model provides a circuit for measuring inductance, the circuit comprising:

[0005] A frequency circuit, the frequency circuit comprising: an oscillator, a varactor diode, an adjustable resistor, and a third resistor;

[0006] The first fixed end of the adjustable resistor is connected to a preset voltage, the second fixed end is grounded, the adjustable end is connected to one end of the third resistor, and the other end of the third resistor is respectively connected to the anode of the varactor diode and the twelfth end of the oscillator;

[0007] The tenth terminal and the twelfth terminal of the oscillator are used as the access terminals of the inductance to be measured, and the third terminal of the oscillator is used as the frequency signal output terminal;

[0008] The frequency signal output end is connected to a frequency meter to measure the frequency value. The frequency meter is connected to a calculator. The calculator outputs and displays the inductance value by calculating the frequency value and a preset capacitance value. The preset capacitance value is the capacitance value of the varactor diode adjusted by the adjustable resistor.

[0009] Wherein, a sixth capacitor is further connected between the third resistor and the twelfth terminal of the oscillator.

[0010] The model of the oscillator is MC1648.

[0011] Wherein, the first terminal and the fourteenth terminal of the oscillator are both connected to the voltage stabilizing and bucking circuit.

[0012] Wherein, the voltage stabilizing and step-down circuit comprises:

[0013] A voltage regulator and a first resistor;

[0014] The voltage output end is connected to the first end of the voltage regulator, that is, the input end of the voltage regulator and step-down circuit, the second end of the voltage regulator is grounded, the third end of the voltage regulator is connected to one end of the first resistor, and the other end of the first resistor is connected to the first end and the fourteenth end of the oscillator as the output end of the voltage regulator and step-down circuit.

[0015] Wherein, the circuit further includes: a first capacitor; one end of the first capacitor is connected between the voltage output end and the first end of the voltage regulator, and the other end of the first capacitor is grounded.

[0016] The other end of the first resistor is also connected to one end of the second capacitor and one end of the fifth capacitor respectively, and the other end of the second capacitor and the other end of the fifth capacitor are both grounded.

[0017] The third end of the oscillator is connected in series with a third capacitor and a second resistor in sequence, and then outputs a frequency signal.

[0018] The tenth end of the oscillator is also connected to one end of the seventh capacitor, and the other end of the seventh capacitor is grounded.

[0019] The fifth end of the oscillator is connected to one end of a fourth capacitor, and the other end of the fourth capacitor is grounded.

[0020] The utility model uses pure hardware, i.e., integrated chip + pure discrete hardware circuit, which can greatly reduce costs and effectively solve the problem of high overall product costs caused by high prices of test frequency instrument products, unstable supply, uncontrollable development cycle, etc. The utility model can accurately and quickly measure the inductance of the inductor, greatly improve the efficiency and accuracy of inductance measurement, and can be applied to industrial production, scientific research, education and other fields. In addition, the utility model has the advantages of low power consumption, simple circuit structure, small space occupation, no need to spend too much debugging time, easy operation, and strong practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1It is a schematic diagram of a circuit for measuring inductance provided by an embodiment of the utility model;

[0023] Figure 2 is a circuit diagram of a frequency circuit provided by an embodiment of the utility model;

[0024] Figure 3 It is a schematic diagram of the RF standard coil provided in the embodiment of the utility model. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0026] Figure 1 is a schematic diagram of an inductance measurement circuit provided by an embodiment of the utility model, Figure 2 This is a circuit diagram of the frequency circuit provided by the embodiment of the utility model, please refer to Figure 1 and Figure 2 , the circuit comprising:

[0027] The frequency circuit 101 includes: an oscillator U2, a varactor diode C8, an adjustable resistor RP1, and a third resistor R3;

[0028] The first fixed end of the adjustable resistor RP1 is connected to a preset voltage, the second fixed end is grounded, the adjustable end is connected to one end of the third resistor R3, and the other end of the third resistor R3 is respectively connected to the positive electrode of the varactor diode C8 and the twelfth end of the oscillator U2;

[0029] The tenth terminal and the twelfth terminal of the oscillator U2 serve as access terminals for the inductor to be measured, and the third terminal of the oscillator U2 serves as a frequency signal output terminal;

[0030] The frequency signal output terminal is connected to a frequency meter 102 to measure the frequency value. The frequency meter 102 is connected to a calculator 103. The calculator 103 outputs and displays the inductance value by calculating the frequency value and a preset capacitance value. The preset capacitance value is the capacitance value of the variable capacitance diode C8 adjusted by the adjustable resistor RP1.

[0031] A sixth capacitor C6 is connected between the third resistor R3 and the twelfth terminal of the oscillator U2.

[0032] The model of the oscillator U2 is MC1648.

[0033] Wherein, the first terminal and the fourteenth terminal of the oscillator U2 are both connected to the voltage stabilizing and bucking circuit.

[0034] Wherein, the voltage stabilizing and step-down circuit comprises:

[0035] A voltage regulator U1 and a first resistor R1;

[0036] The voltage output end is connected to the first end of the voltage regulator U1, that is, the input end of the voltage regulator and buck circuit, the second end of the voltage regulator U1 is grounded, the third end of the voltage regulator U1 is connected to one end of the first resistor R1, and the other end of the first resistor R1 is connected to the first end and the fourteenth end of the oscillator U1 as the output end of the voltage regulator and buck circuit.

[0037] The circuit further includes: a first capacitor C1; one end of the first capacitor C1 is connected between the voltage output end and the first end of the voltage regulator, and the other end of the first capacitor C1 is grounded.

[0038] The other end of the first resistor R1 is also connected to one end of the second capacitor C2 and one end of the fifth capacitor C5 respectively, and the other end of the second capacitor C2 and the other end of the fifth capacitor C5 are both grounded.

[0039] The third end of the oscillator U2 is connected in series with a third capacitor C3 and a second resistor R2 in sequence, and then outputs a frequency signal.

[0040] The tenth terminal of the oscillator U2 is also connected to one end of the seventh capacitor C7, and the other end of the seventh capacitor C7 is grounded.

[0041] The fifth end of the oscillator U2 is connected to one end of a fourth capacitor C4, and the other end of the fourth capacitor C4 is grounded.

[0042] The utility model measures the inductance value by the resonance method, and the measurement lower limit can reach 10nH. The measurement range is very wide and can meet the inductance measurement under normal circumstances. The core device of the utility model is the integrated voltage-controlled oscillator chip U2, model MC1648, which is commonly used in phase-locked loop circuits. By using its voltage-controlled characteristics to generate a frequency signal at the output pin 3, the inductance LX value to be measured can be indirectly measured with extremely high measurement accuracy. MC1648 uses +5V / -5V working voltage, input +15V voltage, through filter capacitor C1 = 100uf, three-terminal integrated voltage regulator ICU1, model LM7805, through resistor R1 = 2.4Ω, filter capacitor C2 = 10uf; C5 = 0.1uf, to provide stable +5v DC voltage output for the 1st and 14th pins of the chip MC1648, the 3rd pin of the chip is composed of R2 = 1.2K, C3 = 470nf to form an RC circuit, the 5th pin is the internal AGC circuit, C4 = 470nf, the 7th and 8th pins of the chip are grounded GND. The 10th pin of the chip, C7 = 470nf measures the measured inductance A end; the measured inductance B end is composed of capacitor C6 = 470nf, variable capacitance diode C8 = BB809, R3 = 100K, and adjustable resistor RP1 = 10K. The voltage across the varactor diode is divided by the potentiometer RP1 to +15V. Different voltage outputs can be obtained by adjusting the potentiometer RP1. This voltage is added to the varactor diode BB809 through R3 to obtain different capacitances. When measuring the measured inductance LX, just connect LX to points A and B in the figure, and then adjust the potentiometer RP1 to make the circuit resonate. An oscillation signal of a certain frequency will be output at the 3rd pin of MC1648. The frequency value of point C can be measured with a frequency meter, and the LX value can be calculated.

[0043] Circuit resonant frequency:

[0044]

[0045] That is, LX = 1 / 4π2f0 2 C

[0046] In the above formula, the resonant frequency f0 is the output frequency value of the 3rd pin of MC1648, and point C is the capacitance value of the varactor diode adjusted by the potentiometer, i.e. the variable resistor RP1. It can be seen that to calculate the value of LX, the value of C must be known first. For this purpose, it is necessary to calibrate the corresponding value of the potentiometer RP1 scale and the varactor diode.

[0047] In order to calibrate the capacitance between the varactor diode and the potentiometer, we can make a standard square RF (radio frequency) inductor L0. Figure 3 As shown in the figure, the standard coil inductance is 0.44uH. During calibration, connect the RF coil L0 to Figure 2Adjust the potentiometer RP1 to different scale positions at the A and B ends, and measure the corresponding measurement value at point C. Then, according to the above resonance formula, the capacitance of the varactor diode at different scales of the potentiometer RR1 dial can be calculated.

[0048] The attached table gives the corresponding relationship of the measured sampling, as follows:

[0049] Oscillation frequency(MHz) Varactor diode C value 98 6 76 10 62 15 53 20 43 30 38 40 34 50

[0050] When making it, you need to make a dial on the multi-turn potentiometer shaft and add a pointer. Figure 3 The given dimensions are self-made. The circuit can work properly if it is installed correctly. Adjust the potentiometer RP1 to obtain the corresponding relationship between the sliding points and the variable capacitance diode to ensure convenient measurement. This measurement method belongs to indirect measurement, but the measurement range is wide and the measurement is accurate, so it is desirable for electronic enthusiasts and laboratories to detect inductance. If the inductance is fixed, the device can be turned into a signal generator with adjustable frequency. The circuit structure is simple. As long as the welding is carried out according to the circuit diagram and the components are selected correctly, it can work normally without debugging.

[0051] The utility model uses pure hardware, i.e., integrated chip + pure discrete hardware circuit, which can greatly reduce costs and effectively solve the problem of high overall product costs caused by high prices of test frequency instrument products, unstable supply, uncontrollable development cycle, etc. The utility model can accurately and quickly measure the inductance of the inductor, greatly improve the efficiency and accuracy of inductance measurement, and can be applied to industrial production, scientific research, education and other fields. In addition, the utility model has the advantages of low power consumption, simple circuit structure, small space occupation, no need to spend too much debugging time, easy operation, and strong practicality.

[0052] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and substitutions can be made without departing from the technical principle of the present invention. These improvements and substitutions should also be regarded as the protection scope of the present invention.

Claims

1. A circuit for measuring inductance, characterized in that: include: A frequency circuit, the frequency circuit comprising: an oscillator, a varactor diode, an adjustable resistor, and a third resistor; The first fixed end of the adjustable resistor is connected to a preset voltage, the second fixed end is grounded, the adjustable end is connected to one end of the third resistor, the other end of the third resistor is respectively connected to the positive electrode of the varactor diode and the twelfth end of the oscillator, the tenth end and the twelfth end of the oscillator serve as the access ends of the inductance to be measured, and the third end of the oscillator serves as the frequency signal output end; The frequency signal output end is connected to a frequency meter to measure the frequency value. The frequency meter is connected to a calculator. The calculator outputs and displays the inductance value by calculating the frequency value and a preset capacitance value. The preset capacitance value is the capacitance value of the varactor diode adjusted by the adjustable resistor.

2. The inductance measuring circuit according to claim 1, wherein: A sixth capacitor is also connected between the third resistor and the twelfth terminal of the oscillator.

3. The inductance measuring circuit according to claim 1, wherein: The model of the oscillator is MC1648.

4. The inductance measuring circuit according to claim 1, wherein: The first terminal and the fourteenth terminal of the oscillator are both connected to the voltage stabilizing and step-down circuit.

5. The inductance measuring circuit according to claim 4, characterized in that: The voltage stabilizing and step-down circuit comprises: A voltage regulator and a first resistor; The voltage output end is connected to the first end of the voltage regulator, that is, the input end of the voltage regulator and step-down circuit, the second end of the voltage regulator is grounded, the third end of the voltage regulator is connected to one end of the first resistor, and the other end of the first resistor is connected to the first end and the fourteenth end of the oscillator as the output end of the voltage regulator and step-down circuit.

6. The inductance measuring circuit according to claim 5, characterized in that: The circuit further includes: a first capacitor; one end of the first capacitor is connected between the voltage output end and the first end of the voltage regulator, and the other end of the first capacitor is grounded.

7. The inductance measuring circuit according to claim 5, characterized in that: The other end of the first resistor is also connected to one end of the second capacitor and one end of the fifth capacitor respectively, and the other end of the second capacitor and the other end of the fifth capacitor are both grounded.

8. The inductance measuring circuit according to claim 1, wherein: The third end of the oscillator is connected in series with a third capacitor and a second resistor in sequence, and then outputs a frequency signal.

9. The inductance measuring circuit according to claim 1, wherein: The tenth terminal of the oscillator is also connected to one end of a seventh capacitor, and the other end of the seventh capacitor is grounded.

10. The inductance measuring circuit according to claim 1, wherein: The fifth end of the oscillator is connected to one end of a fourth capacitor, and the other end of the fourth capacitor is grounded.

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