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ELECTRODYNAMOMETER
WATTMETER'S
•
These instruments are similar in design and construction to electrodynamometer
type ammeters and voltmeters
...
•
The fixed coils or “field coils” arc connected in series with the load and so
carry the current in the circuit
...
C
...
•
The moving coil is connected across the voltage and, therefore, carries a current
proportional to the voltage
...
• Since the moving coil carries a current proportional to the voltage, it is called
the „„pressure coil‟‟ or “voltage coil” or simply called P
...
of the wattmeter
...
•
They are divided into two halves
...
•
The fixed coils are wound with heavy wire
...
•
The fixed coils of earlier wattmeters were designed to carry a current of 100 A
but modem designs usually limit the maximum current ranges of wattmeters to
about 20 A
...
(fig) Dynamometer wattmeter
Moving Coil
•
The moving coil is mounted on a pivoted spindle and is entirely embraced by
the fixed spindle & is entirely embraced b the fixed current coils
...
•
The use of moving coil as pressure coil is a natural consequence of design
requirements
...
Control
• Spring control is used for the instrument
...
•
The moving system carries a light aluminium vane which moves in a sector
shaped box
...
Scales and Pointers
•
They are equipped with mirror type scales and knife edge pointers to remove
reading errors due to parallax
...
Source: http://mediatoget
...
in/2012/01/electrodynamometerwattmeters