In the PMMC type instrument, the deflection is directly proportional to the current flowing through the instrument, we get a uniform scale for the instrument. It gives a uniform scale of upto 270° or more. Td ∝ I
Skin Effect The steady direct current distributes itself uniformly over the whole section of a conductor but the alternating current does not distribute uniformly rather than it tends to concentrate near the surface of a conductor. In fact in the AC system, no current flows through the core and the entire current is concentric at the surface regions. This phenomenon is called skin effect. The skin effect causes the effective resistance of the conductor to increase with the frequency of the current. The skin effect is due to eddy currents set up by the AC current. The skin effect has practical consequences in the design of radiofrequency and microwave circuits and to some extent in AC electrical power transmission and distribution systems.
Form factor: The ratio of r.m.s (or effective) value to average value is the form factor (Kf) of the Waveform. It has used in voltage generation and instrument correction factors. Peak factor: The ratio of maximum value to the r.m.s value is the peak factor (Kp) of the waveform. Form Factor × Peak Factor = (RMS Value / Average Value) * (Maximum Value / RMS Value) = Maximum Value / Average Value
EXAMIANS