Electrodynamic Frequency Meter
Electrodynamic frequency meter/moving coil frequency meters
are ratiometer type of instruments. These meters are used to measure the
frequency of high voltage ranges and for too low voltage ranges. These frequency
meters provide accurate frequency readings. These frequency meters consist
of two moving coils and a rectifier circuit.
Construction
This frequency meter consists of the two moving coils connected
to each other at right angles on a shaft and a pointer is also
connected with this shaft. These two moving coils are connected with their bridge
rectifiers. This circuit consists of a capacitor which is connected
in series with the bridge rectifier of the first moving coil C1 connected to DC
Supply. The direct current (rectified current) flows through a series
resistance to the bridge rectifier and to the second coil C2.
Range
These meters depend on the value of resistance and a capacitor. These
frequency meters have ranges of 40 to 60 Hz, 1200 to 2000Hz and 8000 to
12000Hz.
Working of Electrodynamic Frequency Meter
When the frequency is connected to the supply, the
rectified currents I1 and I2 pass through the moving coil C1 and C2. When these
coils come to rest position, their torques becomes equal but in opposite
direction.
Advantages
These frequency meters have linear frequency scales.
The readings are independent from voltages.
These frequency meters can be used over a wide range of voltage
and at too low voltage range.
Disadvantage
The rectifiers produce distortions which results as an
inaccurate reading of frequency.