electronic finder. Scheme, description

electronic finder. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Indicators, detectors, metal detectors

Beat metal detectors are insensitive when searching for metals with weak ferromagnetic properties, such as, for example, copper, tin, silver. It is impossible to increase the sensitivity of metal detectors of this type, since the frequency difference - beats is hardly noticeable with conventional indication methods. A significant effect is the use of quartz metal detectors.

An electronic seeker, the schematic diagram of which is shown in Fig. 1, consists of a measuring oscillator assembled on a transistor T1 and a buffer stage - an emitter follower assembled on a transistor T2, separated by quartz Kv1 from an indicator device-detector on a diode D2 with a DC amplifier on a transistor T3. The load of the UPT is a pointer device with a total deflection current of 1 mA.

electronic finder
Ris.1

Due to the high quality factor of quartz, the slightest changes in the frequency of the measuring oscillator will lead to a decrease in the impedance of the latter, as can be seen from the characteristic shown in Fig. 2, and this, ultimately, leads to an increase in the sensitivity and accuracy of the reading.

electronic finder
Ris.2

Preparation for the search consists in tuning the oscillator to the parallel resonance frequency of quartz equal to 1 MHz. This adjustment is made by capacitors of variable capacitance C2 (roughly) and trimmer capacitor C1 (finely) in the absence of metal objects near the frame. Since quartz is an element of communication between the measuring and indicating parts of the device, its resistance at the time of resonance is large and the minimum reading of the pointer device indicates the fine tuning of the device.

Otherwise, working with the device does not differ from that with metal detectors on beats. The sensitivity level is regulated by a variable resistor R8.

A feature of the device is the ring frame L1, made from a piece of cable. The central core of the cable is removed and instead of it 6 turns of PEL 0,1-0,2 type wire 115 mm long are pulled through. The design of the frame and the order of conclusions are shown in Fig.3. Such a frame has a high quality factor and a good electrostatic screen. The rigidity of the frame structure is ensured by placing it between two discs made of plywood or getinaks with a diameter of 400 and a thickness of 5-7 mm.

electronic finder
Ris.3

The device can be used transistors KT315B, silicon reference diode 2S156A. detector diode type D9 with any letter index. The quartz frequency can be in the frequency range from 900 kHz to 1,1 MHz. Cable RK-50.

Literature

"Radio-Electronics", 1967, No. 11.
Radio No. 2 1970

Publication: N. Bolshakov, rf.atnn.ru

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