Friends, today in this article we will learn about the structure of permanent magnet moving coil device. I am going to give information about all this in a very good way. So let’s start.
Working Principle
When the device is connected to the supply, current flows in the coil through the spring. When in a magnetic field, a deflection force is applied on the coil, due to which the coil rotates on its spindle and the indicator mounted on the spindle shows the reading on the graduated scale. The deflection obtained on the scale is proportional to the current flowing in the coil.
Construction
It has a permanent horse shoe shaped dipole magnet. A rectangular coil between the poles is wrapped with a thin copper wire on a light aluminum form in which many turns are given. The coil is placed on a soft iron core stationary in the middle of the magnetic field. The soft core reduces the reluctance between the poles. A Phosphorus bronze hair spring is fitted on the spindle placed in the middle of the coil to give the controlling torque, wound in opposite directions above and below the coil. The effect of heat is neutralized by applying the hair spring in the opposite direction.
Electric current flows in the coil through a Phosphorus bronze spring. The function of the spring is to give the controlling torque to the instrument. A light pointer is fitted on the spindle of the coil. The pointer displays the value of current or voltage on the scale of a calibrated dial.
The spindle is pivoted on a diamond cone shaped bearing. The details of the instrument are given in symbols on the dial. A screw is fitted to adjust the pointer to zero.
Applications
When PMMC is used as an ammeter, the moving coil is connected relative to a low resistance shunt so that only a small part of the main current flows through the coil.
When PMMC is used as a voltmeter, the coil is connected in series with a high resistance. Due to which the moving coil can be used as an ammeter or voltmeter. The error caused due to temperature in using it is eliminated.
What did you learn today: –
Now you must have known the structure of a permanent magnet moving coil instrument. You must have got the answer to all these questions well.
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