Which of the following is true for PMMC instruments?

The correct answer is option 2.

Permanent Magnet Moving Coil (PMMC)

Characteristics of PMMC instrument

•  ​PMMC is used to measure only DC or the average value of electrical quantity.
• The PMMC instrument has a linear or uniform scale, hence the deflecting torque produced is directly proportional to the current.
• Either spring or gravity control can produce the controlling torque in PMMC instruments.
• For spring control: Tc ∝ θ  and For gravity control: Tc ∝ sin θ 
• The damping torque in the PMMC instrument is provided by eddy current damping.

Advantages

• The PMMC has a high torque-to-weight ratio.
• The PMMC consumes less power and has great accuracy.
• It produces no losses due to hysteresis.
• It has efficient damping characteristics and is not affected by a stray magnetic field.
• PMMC instruments use a permanent magnet and a moving coil to measure current or voltage. They do not have iron parts that can suffer from magnetic hysteresis loss.

Disadvantages

• Moving coil instruments are expensive.
• The moving coil instrument can only be used on the D.C. supply as the current reversal produces a torque on the coil.
• It may show an error due to the permanent magnet's magnetism loss.