Range Extension of Instrument

Range Extension of Instrument Points : Range Extension of Instrument The range of an electrical instrument is limited by the current, which can be carried by the coil of the instrument safely. For example the moving coil and the spiral springs used as a coil connections can be designed for a maximum current of only about 50 milli-amperes and a potential drop of about 50 mull-volts. Hence for measurement of large current or voltage or power same means for increasing the range of the instrument are to be adapted.

There are four common devices employed for extending the range of instruments; these are:-
i) Shunts
ii) Multipliers
iii) Current Transformers (C.T.)
iv) Potential Transformers (P.T.)

When instruments are connected with such external devices, the instrument is calibrated and its scale is correspondingly marked over the range of the associated shunt, multiplier or instrument transformer.