Moving Coil (MC) Instruments Advantages Disadvantages

The operation of moving coil meters depends on the electromagnetic effect of the current ( a force is excerted on the current carrying conductor when placed in a magentic field )

Moving coil instruments are of two types:

• Permanent magnet type
• Dynamometer type

Permanent magnet type moving coil instruments can be used only in measuring dc circuits whereas Dynamometer type moving coil meters can be ued to measure both ac and dc circuits

Some of the advantages and disadvantages of moving coil instruments are given below:

Merits or Advantages:

• Moving coil instruments consume quite less power. This is becasue the resistance of moving coil is small
• In Moving coil meters the ratio of torque to weight is quite high and this reduces the errors due to friction
• The scale of moving coil instrument is uniform
• A low range ammeter can be used as both ammeter and voltmeter to measure high currents and voltages
• PMMC meters are free from errors which would be caused by hysteresis and stray magnetic fields
• Damping is very simple and effective in moving coil meters

Demerits or Disadvantages:

• Due to friction at the bearings and temperature variations, errors are likely to be presentand the observed readings are may not be accurate and fresh calibration of the meters may become necessary
• With long usage permanent magnet gets weakened and this likely may introduce errors in readings