In electronic production and design, the inductance coils of different parameters are often used, and the inductance of these coils is not as easy as the resistor, and some digital multimeters have inductive measuring gears, but the measurement range is limited. The circuit measures the electrical value in a resonant method, the lower limit of the measurement can reach 10nH, the measurement range is wide, can meet the inductance measurement under normal circumstances, the circuit structure is simple, and the work is reliable and stable, suitable for fan making.
First, the principle of circuit working principle is shown in Figure 1 (a).
The core device of this circuit is an integrated voltage-controlled oscillator chip MC1648 that utilizes its voltage control characteristics to generate a frequency signal in output 3 foot, and can be used indirectly to measure the inductance Lx value, which is extremely high. The BB809 is a variable diode, and the potentiometer VR1 is divided into + 15V, and the potentiometer can obtain a different voltage output, which is applied to the variable diode BB 80 9 to obtain different capacitances. When measuring the measured inductance Lx, simply connect LX in two points in the drawings, then adjust the potentiometer VR1 to resonate the circuit, and output a certain frequency of oscillation signals in the 3 foot of the MC1648, and measure the C point with frequency meter. The frequency value can be obtained by calculating the LX value.
Circuit resonant frequency: f0 = 1 / 2π lxc so lx = 1 / 4π 2 f 2c
The resonant frequency f0 is the 3 pin output frequency value of the MC1648, and c is the capacitance value of the varactor diode modulated by the potentiometer VR1, and the value to calculate the LX must know the C value first. To this end, it is necessary to calibrate the potentiometer VR1 scale to the corresponding value of the beam diode. In order to calibrate the capacitance between the vane diode and the potentiometer, we have to make a standard square RF (radio frequency) inductor coil L0. As shown in Figures 6-7 (b), the standard coil inductor is 0.44 μH. When the calibration, the RF coil L0 is connected at both ends of the A, B of Fig. (A), and the potentiometer VR1 is adjusted to different scale positions, and the corresponding measured value can be measured at the C point, and then calculates according to the above resonant formula. The diode is different from the capacitance of the potentiometer VR1 tick disc.
Second, the components Select Integrated Circuit IC Select Motoroia's VCO (voltage controlled oscillator) chip. VR1 Selects a multi-circle high precision potentiometer. Other components can be selected according to the circuit diagram.
3. When making and debugging the method, you need to make a tick disk on the multi-ring potentiometer shaft and bring the pointer. The RF standard coil is self-made according to the picture (b). The circuit is installed correctly, adjusting the corresponding relationship between multiple points of the potentiometer VR1 taking the slide and the corresponding relationship of the beam diode, ensuring convenient measurement. The measurement method belongs to indirect measurements, but the measurement range is wide, accurate measurement, so it is possible to obtain electronic enthusiasts and laboratory detection. When the device can become a signal generator that can be modulated frequently
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