Construction and working principle of moving coil instruments
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Working principle and construction ofPMMC. ... The PMMC works on the electromagnetic effect. A permanent magnet is used to produce magnetic flux and a coil that carries the current to be measured moves in this field. As the pointer is connected to the coil it gets deflected in proportion with the current.The basic construction of PMMC is shown in above fig. a light rectangular coil wound on an aluminum frame is pivoted within the air gaps between the two poles of a permanent magnet and a cylindrical soft iron core. This light rectangular coil carries the current to be measured. Soft iron core provides formation of uniform magnetic field. The aluminum frame supports the coil as well as provides eddy current damping. Two phosphor bronze springs coiled in opposite directions serve as leads for the current in the coil. The springs also provide controlling torque.
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