Views:0 Author:Site Editor Publish Time: 2019-07-12 Origin:Site
The food metal detector is a special instrument for detecting metal. In addition to the metal shell used to detect mines or metal parts, it can also be used to detect wires hidden in the wall, underground pipes and cables, and even treasures that can be touched. Found a metal object buried in the ground. Metal detectors can also be used as a tool for youth defense education and popular science, and certainly an interesting toy. It is mainly used for the detection of ferrous and non-ferrous metals in meat, fungi, confectionery, beverages, food, fruits, vegetables, dairy products, aquatic products, health products, additives and condiments. Detection of metal impurities in chemical raw materials, rubber, plastics, textiles, leather, chemical fiber, toys, medicines, health products, biological products, cosmetics, gifts, packaging, paper products. How food metal detectors work
The high frequency oscillator consists of a triode VT1 and a high frequency transformer T1, which is a transformer feedback LC oscillator. T1 and capacitor C1 are composed of an LC parallel oscillating circuit whose oscillation frequency is about 200 kHz, which is determined by the inductance of L1 and the capacitance of C1. The secondary coil L2 of T1 is the feedback coil of the vibrator, its "C" terminal is connected to the bottom end of VT1, and "D" is terminated by VD2. Since VD2 is in a positive wizard mode, the "D" terminal can be considered as the ground for high frequency signals. In the high-frequency transformer T1, if "A" and "D" at one end are respectively input from "C" to the secondary coil winding direction of the VT1 oscillating tube of the feedback signal, the circuit can form positive feedback and generate self-excitation Frequency oscillation. The magnitude of the oscillator feedback voltage is related to the turn ratio of the coils L1 and L2. The turn ratio is too small. Since the feedback is too weak, it is difficult to start, resulting in distortion of the oscillation waveform, and the sensitivity of the metal detector is greatly reduced. The bias circuit of the oscillating tube VT1 is composed of R2 and a diode VD2, which is the current limiting resistance of VD2. Since the front threshold voltage of the diode is constant (about 0.7 volts), the base of the secondary coil L2 is added to VT1 to obtain a stable bias voltage.
How food metal detectors work
The stability of the VT1 high frequency oscillator can be greatly improved by this type of stabilizer. In order to further improve the sensitivity and reliability of the metal detector, the sensitivity and reliability of the metal detector are improved by the regulated power supply circuit, the Zener diode VD1 circuit, the current limiting resistor, the R6 and the decoupling capacitor C5. There are two sets of potentiometers in the emitter and indirect of the oscillating tube VT1, which has the negative feedback effect of the emitter current. The larger the resistance value, the stronger the negative feedback effect, the lower the VT1 amplification capability, and even the circuit oscillation stops. RP1 is the coarse potentiometer for the oscillator gain and RP2 is a trim potentiometer.