Advantages and disadvantages of PMMC (permanent magnet moving coil)

There are some advantages of PMMC (permanent magnet moving coil) are given below,

• The PMMC has uniformly divided scale. The scale may be very long, over about 250 degree.
• It has a very high torque to weight ratio.
• The PMMC has consumes low power.
• The PMMC has a very high accuracy.
• The PMMC is free from hysteresis error.
• The PMMC has efficient damping characteristics and is not affected by stray magnetic field.
• Extension of instrument range is possible with the help of shunt and series resistances.

There are some disadvantages of PMMC (permanent magnet moving coil) are given below,

• It has comparatively high cost.
• The PMMC has only suitable for d.c. measurements.
• Aging of permanent magnets and control springs introduces errors.