Permanent magnet moving coil
(PMMC)
An opposing effect is built in the instrument which tries to oppose the deflection or the mechanical displacement of the moving system. The opposing effect is closely related to the defection or mechanical displacement which can be directly observed. The opposing effect is so designed that it magnitude increases with the increase of eflection or mechanical displacement of the moving system caused by the quantity under measurement. The balance is achieved when opposing effect equal to cause producing the deflection or mechanical movement. The defection or mechanical movement. The value of the measured quantity can then be inferred from the deflection or mechanical displacement at the point of balance.
Example PMMC :-
PMMC in a use ammeter, the deflection of the moving coil is proportionl of the cunnent I the quantity under measurement. The torque acting on the moving coil is proportionl to current or which is dependent upon flux density, number of turns and area of moving coil. The opposing effect is produced by a spring whose torque is proportionl to deflection or where is the spring contant whose value depends upon materil and the dimension of the spring. Under the condition of balance or deflection and current.
The value of measured quantity, cunnent, in this case dependent upon the value of deflection and the constants of the meter. thus, in order to make the instrument direct reading, it reads the value of current direction in terms of terms of the deflection, it will have to be calibrated to make into consideration by value G and K.
we conclude in a deflection type instrument the value of measured quantity depends upon the calibration of the instrument.
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