Which of the following meters has the best accuracy?

The correct answer is option 2): (Moving-coil meter)

Concept:

PMMC instruments:

PMMC instrument is also called D'Arsonval meter.

These are used to measure the current and voltage in the DC circuit.

They are used eddy current-type damping

Eddy current damping:  

• When a conductor moves in a magnetic field an emf is induced in it and if a closed path is provided, a current (known as eddy current) flows
• This current interacts with the magnetic field to produce an electromagnet torque which opposes the motion
• This torque is proportional to the strength of the magnetic field and the current produced T
• Here are two common forms of eddy current damping devices:

1.  A metal former that carries the working coil of the instrument
2. A thin aluminum disc is attached to the moving system of the instrument, this disc moves in the field of a permanent magnet; The disc should be of conducting and non-magnetic material

Additional InformationAdvantages:

• The scale is uniform (Linear scale) High torque to weight ratio compared to all the other types of instruments Frequency error or reactance error is absent
• High sensitivity
• Hysteresis loss is zero
• No internal heating problem
• High accuracy
• Very less power consumption

Disadvantages:

It works only for Dc not used for AC Cost is very high