Extending the Range of Ammeters and Voltmeters
The ranges of electrical measuring instruments (whether
ammeter, voltmeter or any other type of meters) are limited by the currents,
which be carried by the coils of the instruments safely. For example, the moving
coils of the instruments can carry maximum current of about 50 mA safely and
the potential drop across the moving coil is about 50 mV. Hence, it becomes
necessary that the current and voltage being measured be reduced and brought
within the range of instrument.
There are four common devices used for extending the range of
the instruments, namely \
1. Shunts
2. Multipliers
3. Current transformers
4. Potential transformers
The let us discuss the first two topics i.e. shunts and
multipliers
1. Shunts: The range of an ammeters can be
extended by connecting a low resistance, called shunts, connected in parallel
with ammeter. The shunt by passes the extra current and allows only safe
current