Metal detectors OR (Off Resonance), theory. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Metal detectors OR (Off Resonance), theory. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / metal detectors

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Interesting circuit solutions can be found when considering the designs of metal detectors, the operation of which is based on the principle of estimating the change in the amplitude of the signal on the circuit coil, the resonant frequency of which is close to the frequency of the reference oscillator signal applied to it. The main advantage of such devices, sometimes referred to as OR (Off Resonance), is simplicity and reliability (Fig. 1.3).

Metal detectors OR (Off Resonance), theory
Rice. 1.3. Simplified block diagram of a near-resonant frequency metal detector

The measuring coil is an integral part of the oscillatory circuit, the resonant frequency of which differs slightly from the frequency of the reference oscillator. When a metal object appears in the zone of the electromagnetic field excited by the measuring coil, the resonant frequency of this circuit changes. Depending on what metal is in the coverage area of this device (colored or black), the frequency of the circuit either increases or decreases. In this case, corresponding changes in the amplitude of oscillations of the reference oscillator occur, which are evaluated by the analyzer. As a result, the analyzer generates a control signal for the display unit.

Author: Adamenko M.V.

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