Metallic detector applies a principle, the principle of metallic detector
From;    Author:Stand originally

Mention metallic detector, people can associate to mine detector, engineer explores the landmine of bury with it. Metallic detector is a kind of instrument that uses exploration metal technically, besides the landmine that is used at exploring to have metallic crust or metallic part, still can use explore concealment the electrical wiring inside wall, bury in subterranean conduit and cable, even can subterranean explore treasure, discover bury is in subterranean metal object, of course, now metallic detector more be used on industrial utility, for instance food metal impurity is explored - food metal exploration machine, metal of factory metal guard against theft is explored- - the metal explores the door, install check gate, the impurity of the metal that break a needle of textile is explored - check needle machine. Metallic detector still can serve as the apparatus that develops education of teenage national defence and popular science activity, of course also can yet be regarded as is a kind of interesting recreation toy.

Working principle

High frequency oscillator
By dynatron VT1 and high frequency transformer the composition such as T1, it is oscillator of feedback of a kind of transformer LC. The primary coil L1 of T1 and capacitor C1 form loop of LC shunt-wound oscillation, its oscillation frequency makes an appointment with 200kHz, by the inductance of L1 the capacitance of quantity and C1 is decided. The secondary coil L2 of T1 regards the feedback of the oscillator as coil, its " C " the base of VT1 of termination oscillation canal, "D " termination VD2. Because VD2 is in to on-state, to high frequency signal, "D " end can regard ground connection as. In high frequency transformer in T1, if " A " and " D " end is respectively first, the head end that secondary coil winds line way, criterion from " C " the feedback signal that carries an input to provide VT1 base to oscillation, can make circuit is formed feedbacking and produce self-excitation high frequency oscillation. The v/LIT all over the ground number of the size of oscillator feedback voltage and coil L1, L2 is compared about, v/LIT all over the ground number is smaller than passing, because feedback is too weak, not allow Yi Qizhen, cause oscillation weaveform greatly too lack fidelity, still can make metallic detector sensitivity is reduced greatly. Of oscillation canal VT1 slant buy circuit is comprised by R2 and diode VD2, r2 is the current limliting resistor of VD2. As a result of diode to threshold value voltage constant (make an appointment with 0.7V) , increase the base of VT1 through secondary coil L2, in order to get stable bias voltage. Apparent, of type of this kind of stabilized voltage slant buy circuit can enhance VT1 greatly the stability of high frequency oscillator. To heighten the dependability of metallic detector and sensitivity further, high frequency oscillator carries power supply of stabilized voltage circuit, its circuit by resistor of VD1 of stabilized voltage diode, current limliting R6 is mixed go C5 comprises Ou capacitor. Oscillation canal VT1 blasts off extremely the has two series secondhand potentiometer with the ground, have blast off extremely electric current suffers feedback effect, its resistance is greater, negative feedback action is stronger, the enlarge capacity of VT1 is smaller also, make circuit stops even brace up. RP1 is the coarse adjustment potentiometer of oscillator gain, RP2 is thin tone potentiometer.
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