Electrical Resonance Type Frequency meter.

 Frequency Meter :- These are used to measure supply frequency. These are used at generating stations & substations. A frequency meter is an instrument that displays the frequency of a periodic electrical signal.

Electrical Resonance Type Frequency Meter :- It is a type of frequency meter which is used to measure frequency range 45 Hz to 55 Hz of AC supply.

Construction :- It consists of a fixed coil which is connected across the supply whose frequency is to be measured. This coil is called magnetizing coil. The magnetizing coil is mounted on a laminated iron core. The iron core has a cross-section which varies gradually over the length, being maximum near the end where the magnetizing coil is mounted & minimum at the other end. A moving coil is pivoted over this iron core. A pointer is attached to the moving coil. The terminals of the moving coil are connected to a suitable capacitor C. There is no provision for a controlling force.

Working :- Due to the current in the moving coil, the moving coil produces a flux in phase with the current. This flux flows along with the extended core of the fixed coil, Therefore the flux links the moving coil. Hence, the flux induces an emf across the moving coil. Obviously, this induced emf lags the flux by 90°. Since it is a coil; the moving coil will have some inductive reactance. Again, as it is connected across a capacitor, it will have some capacitive reactance also.

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