A choke coil is simply a coil having a large inductance, but a small resistance. A device that can regulate the current in an A.C. circuit without much loss of energy is called as ‘choke coil’.
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
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