The error due to hysteresis in moving iron type instrument is minimized by using
Right Answer is:
The error due to hysteresis in moving iron-type instruments is minimized by using Stainless steel.
Error due to Hysteresis
This source of error is due to hysteresis in the soft Iron part, due to which too high values are recorded by the instrument when the current is increasing and too low readings are liable to be indicated when the current is decreasing.
Hysteresis Loss = Kh × BM1.67 × f × v watts
where Kh is the Hysteresis coefficient depends upon the material. The smaller the value of Kh of a magnetic material, the lesser is the hysteresis loss. The armatures of electrical machines and transformer cores are made of magnetic materials having low hysteresis coefficient in order to reduce the hysteresis loss. The steels have Kh values around 130, for cast steel they are around 2500, and for cast iron about 3750.
Errors due to Stray fields:- External stray magnetic fields are liable to affect adversely the accurate functioning of the instrument. Magnetic shielding of the working parts is obtained by using a covering of cast iron.
Errors with A.C only
Errors may be caused due to change km frequency because the change in frequency produces (i) change in impedance of the coil and (ii) change in magnitude of eddy currents. The error due to the former is negligible in ammeters, as the coil current is determined by the external circuit and the error due to the latter can normally be made small.