Which of the following meters is the most accurate instrument for measuring AC signals with frequencies lower than 200 Hz?

Advantages of Electrodynamic instruments:

• Air cored coils are used, they are generally free from hysteresis and eddy current errors when used on AC circuits.
• These instruments can be used for both DC. and AC measurements.
• It is the most accurate instrument for measuring AC signals with frequencies lower than 200 Hz.
• It has precision grade accuracy when used as a wattmeter.
• Less power consumption.

Disadvantages of Electrodynamic instruments:

• Air-cored coils are used, the operating magnetic field of these instruments is so weak that considerable errors may be introduced due to stray magnetic fields and in order to protect them, they must be shielded with cast-iron cases.
• Energy must be used to create two magnetic fields, such instruments are relatively insensitive or having low sensitivity.
• The power required is generally greater than that required by the permanent-magnet type owing to the greater weight of the moving parts.
• Dynamometer-type ammeters and voltmeters have uneven scales. However, the dynamometer wattmeter has a uniform scale.
• They are more expensive than the permanent-magnet-type instruments