The resonant frequency type utilizes a tuned circuit, the frequency of which represents one logical state,and the detuning of the circuit representing the opposite logical state.In the magnetic saturation method, the inductor is either saturated or nonsaturated. Alternately, the reluctance of the magnetic circuit is effectively translated to logical ones and zeros.Resolution is limited by the size of the magnetized spot and complicated by interaction between magnetized spots on adjacent tracks. Magnetic encoders overcome the basic speed limitation of contact encoders and offer greater longevity by eliminating physical contact between disc and sensor. Also, magnetic encoders function well in environments hostile to contact types where any of the magnetic scanning techniques can be successfully employed. However, high ambient fluxes or radiation densities can destroy the disc pattern or inhibit saturated core operation. Greater precaution against mutual electromagnetic interference is required when magnetic encoders are included in the system. Figure 3-2 illustrates the principle stages of typical magnetic encoding.
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