12-06-2014, 03:15 PM
FREQUENCY METERS SEMINAR
FREQUENCY METERS.ppt (Size: 305.5 KB / Downloads: 20)
CLASSIFICATION
Mechanical resonance type
Electrical resonance type
Weston type
Principle- Mechanical resonance
Upper part of reed- flag
Different weights and dimensions
Reed- which the natural frequency is twice the supply frequency- vibrate more
Advantage
Reading is not affected by the change in waveform of supply voltage.
Disadvantages
Adjacent reed is 0.5
Accuracy depends on proper tuning of reed
Low voltage measurement is not possible
Moving iron type
Works on the changes in current in the parallel circuits
When the frequency changes - one coil is inductive and other one is non inductive-
Frequency is above the normal value- impedance of coil A increase-current reduced- Coil B stronger field- movement of spindle- right side
Fixed coil-magnetizing coil-same frequency of supply
Moving coil-carries a pointer
Measure phase difference between two signals
Deflection of full cycle is zero, when Vs is zero
D1 and D2 providing rectifier action