<P> The linear variable differential transformer (LVDT) (also called linear variable displacement transformer, linear variable displacement transducer, or simply differential transformer) is a type of electrical transformer used for measuring linear displacement (position). A counterpart to this device that is used for measuring rotary displacement is called a rotary variable differential transformer (RVDT). </P> <P> LVDTs are robust, absolute linear position / displacement transducers; inherently frictionless, they have a virtually infinite cycle life when properly used . As AC operated LVDTs do not contain any electronics, they can be designed to operate at cryogenic temperatures or up to 1200 ° F (650 ° C), in harsh environments, under high vibration and shock levels . LVDTs have been widely used in applications such as power turbines, hydraulics, automation, aircraft, satellites, nuclear reactors, and many others . These transducers have low hysteresis and excellent repeatability . </P> <P> The LVDT converts a position or linear displacement from a mechanical reference (zero, or null position) into a proportional electrical signal containing phase (for direction) and amplitude (for distance) information . The LVDT operation does not require an electrical contact between the moving part (probe or core assembly) and the coil assembly, but instead relies on electromagnetic coupling . </P> <P> The linear variable differential transformer has three solenoidal coils placed end - to - end around a tube . The center coil is the primary, and the two outer coils are the top and bottom secondaries . A cylindrical ferromagnetic core, attached to the object whose position is to be measured, slides along the axis of the tube . An alternating current drives the primary and causes a voltage to be induced in each secondary proportional to the length of the core linking to the secondary . The frequency is usually in the range 1 to 10 kHz . </P>

When do you obtain null position in lvdt
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