| 手持金属探测器的原理 |
| 添加时间：2018/7/6 15:52:16 浏览次数： |
| 手持金属探测器的原理 The principle of a handheld metal detector 本手持金属探测器由高频振荡器、振荡检测器、音频振荡器和功率放大器等组成。 The handheld metal detector consists of a high frequency oscillator, an oscillating detector, an audio oscillator and a power amplifier. 高频振荡器 High-frequency oscillator 由三极管VT1和高频变压器T1等组成，是一种变压器反馈型LC振荡器。T1的初级线圈L1和电容器C1组成LC并联振荡回路，其振荡频率约200kHz，由L1的电感量和C1的电容量决定。T1的次级线圈L2作为振荡器的反馈线圈，其“C”端接振荡管VT1的基极，“D”端接VD2。由于VD2处于正向导通状态，对高频信号来说，“D”端可视为接地。在高频变压器T1中，如果“A” 和“D”端分别为初、次级线圈绕线方向的首端，则从“C”端输入到振荡管VT1基极的反馈信号，能够使电路形成正反馈而产生自激高频振荡。振荡器反馈电压的大小与线圈L1、L2的匝数比有关，匝数比过小，由于反馈太弱，不容易起振，过大引起振荡波形失真，还会使手持金属探测器灵敏度大为降低。振荡管VT1的偏置电路由R2和二极管VD2组成，R2为VD2的限流电阻。由于二极管正向阈值电压恒定（约0.7V），通过次级线圈L2加到VT1的基极，以得到稳定的偏置电压。显然，这种稳压式的偏置电路能够大大增强VT1高频振荡器的稳定性。为了进一步提高手持金属探测器的可靠性和灵敏度，高频振荡器通过稳压电路供电，其电路由稳压二极管VD1、限流电阻器R6和去耦电容器C5组成。振荡管VT1发射极与地之间接有两个串联的电位器，具有发射极电流负反馈作用，其电阻值越大，负反馈作用越强，VT1的放大能力也就越低，甚至于使电路停振。RP1为振荡器增益的粗调电位器，RP2为细调电位器。 It is composed of transistor VT1 and high frequency transformer T1. It is a feedback LC oscillator of transformer. The primary coil L1 and capacitor C1 of T1 consist of LC parallel oscillation circuit whose oscillation frequency is about 200kHz, which is determined by the inductance of L1 and the capacitance of C1. The secondary coil L2 of T1 acts as the feedback coil of the oscillator, and its "C" ends connect to the base of the oscillating tube VT1, and the "D" ends with VD2. Because the VD2 is in a positive conduction state, for the high frequency signal, the "D" end can be regarded as grounding. In the high frequency transformer T1, if the "A" and "D" ends are the first ends of the primary and secondary winding direction respectively, the feedback signals from the "C" end are input to the VT1 base of the oscillating tube, which can make the circuit form positive feedback and produce self excited high frequency oscillation. The size of the oscillator's feedback voltage is related to the turn number ratio of the coil L1 and L2. The ratio of the turn number is too small. Because the feedback is too weak, it is not easy to vibration, too large to cause the distortion of the oscillation wave, and the sensitivity of the handheld metal detector will be greatly reduced. The bias circuit of the oscillator tube VT1 is composed of R2 and diode VD2, and R2 is the current limiting resistor of VD2. Because the diode has a positive threshold voltage constant (about 0.7V), the L2 is added to the base of VT1 through the secondary coil to obtain a stable bias voltage. Obviously, this stable bias circuit can greatly enhance the stability of VT1 high frequency oscillator. In order to further improve the reliability and sensitivity of a handheld metal detector, the high frequency oscillator is powered by a voltage regulator circuit, which consists of a voltage regulated diode VD1, a current limiting resistor R6 and a decoupling capacitor C5. The VT1 emitter of the oscillating tube has two series of potentiometers in series between the emitter and the earth, which has the effect of the emitter current negative feedback. The greater the resistance value and the stronger the negative feedback effect, the lower the amplification ability of the VT1, even to stop the circuit. RP1 is the coarse tuning potentiometer for the oscillator gain, and RP2 is the fine tuning potentiometer. 振荡检测器 Oscillating detector 振荡检测器由三极管开关电路和滤波电路组成。开关电路由三极管VT2、二极管 VD2等组成，滤波电路由滤波电阻器R3，滤波电容器C2、C3和C4组成。在开关电路中，VT2的基极与次级线圈L2的“C”端相连，当高频振荡器工作时，经高频变压器T1耦合过来的振荡信号，正半周使VT2导通，VT2集电极输出负脉冲信号，经过π型RC滤波器，在负载电阻器R4上输出低电平信号。当高频振荡器停振荡时，“C”端无振荡信号，又由于二极管VD2接在VT2发射极与地之间，VT2基极被反向偏置，VT2处于可靠的截止状态，VT2集电极为高电平，经过滤波器，在R4上得到高电平信号。由此可见，当高频振荡器正常工作时，在R4上得到低电平信号，停振时，为高电平，由此完成了对振荡器工作状态的检测。 The oscillating detector is composed of a triode switch circuit and a filter circuit. The switch circuit is composed of transistor VT2, diode VD2 and so on. The filter circuit is composed of filter resistor R3, filter capacitor C2, C3 and C4. In the switch circuit, the base of VT2 is connected to the "C" end of the secondary coil L2. When the high frequency oscillator works, the oscillation signal is coupled through the high frequency transformer T1. The VT2 is directed in half a week, the VT2 collector outputs the negative pulse signal, and the low level signal is output on the load resistor R4 through the PI type RC filter. When the high frequency oscillator stops oscillating, the "C" end does not oscillate, and because the diode VD2 is connected between the VT2 emitter and the ground, the VT2 base is reverse offset, the VT2 is in a reliable cut-off state, the VT2 collector is high level, and the high level signal is obtained on the R4 through the filter. It can be seen that when the high frequency oscillator is working normally, the low level signal is obtained on the R4, and the high level is used when the vibration is stopped, thus the detection of the working state of the oscillator is completed. |
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