Ammeters & Multimeters
Ammeters are connected in series:
In the circuit whose current is to be measured. The power loss in an ammeter is I2Ra where I is the current to be measured and R is the resistance of ammeter. Therefore, ammeters should have a low electrical resistance so that they cause a small voltage drop and consequently absorb small power.
Voltmeters are connected in parallel with the circuit whose voltage is to be measured. The power loss in voltmeters is V where V is the voltage U) be measured and R is the resistance of voltmeter. The voltmeters should have a high electrical resistance, in order that the current drawn by them is small and consequently the power consumed is small.
Types of instruments
The main types of instruments used as an ammeters and voltmeters are
(i) Permanent magnet moving coil (PMMC)
(ii) Moving iron
(iii) Electro-dynamometer
(iv) Hot wire
(iv) Thermocouple
(vi) Induction
(vii) Electrostatic
(viii) Rectifier.
