Design of inductive measurement circuit based on MC1648

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 inductance value in a resonant method, and the lower limit of the measurement is 10NH, the measurement range is very wide, which can meet the inductance measurement under normal conditions, the circuit structure is simple, and the work is reliable and stable, suitable for fan making. The core device of the 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. BB809 is a variable diode, and the potentiometer VR1 is divided into + 15V, and the potentiometer can be obtained. Voltage output, the voltage is applied to the beam diode BB809 by R1 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. The harmonic frequency f0 is the 3 pin output frequency value of the MC1648, and c is the capacitance value of the varactor VR1, which is visible, the value to calculate the LX needs to 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.

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