Electrical Engineering ⇒ Topic : Advantages and disadvantages of Dynamometer Type Instruments
(i) These instruments can be used for both d.c. and a.c. measurements
(ii) Since air cored coils are used, they are generally free from hysteresis and eddy current errors when used on a. c. circuits.
(1) Since air-cored coils are used, the operating magnetic field of these instruments is so weak that considerable en-ors may be introduced due to stray magnetic fields and in order to protect them, they must be shielded with cast-iron cases.
(2) Since energy must be used to create two magnetic fields, such instruments are relatively insensitive.
(3) The power required is generally greater than that required by permanent-magnet type owing to the greater weight of the moving parts.
(4) Dynamometer type ammeters and voltmeters have uneven scale. However, dynamometer wattmeters have uniform scale.
(5) They are more expensive than the permanent-magnet type instruments
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