l42 instruments
DESCRIPTION
TRANSCRIPT
Dept of E&E ELE101/102 1
Moving Iron type instruments
•Attraction type•Repulsion type
Basic types:
Principle:
A soft iron vane (moving iron) which is mounted on the spindle moves when the operating current flows through the coil.
Dept of E&E ELE101/102 2
Attraction typeMoving Iron type instruments:
Construction:
When current flows through the coil, a soft iron piece moves from the weaker magnetic field towards the stronger field.
Dept of E&E ELE101/102 3
Attraction typeMoving Iron type instruments:
Working:
Td α mean of i2 over a cycle.
Tc α θ
In steady state, Tc=Td
θ α mean of i2 over a cycle
Scale is not uniform
Dept of E&E ELE101/102 4
Repulsion type
θ α mean of i2 over a cycle
Scale is not uniform
Moving Iron type instruments:
When current flows through the coil, Two soft iron rods get magnetized similarly, causing them to repel each other.
Dept of E&E ELE101/102 5
•Cheap and sturdy.•Possess a good degree of reliability.•Less friction errors
Advantages:
Disadvantages:•Degree of precision of calibration is not high for dc measurements due to hysteresis in iron parts
Moving Iron type instruments
Dept of E&E ELE101/102 6
Measurement of POWER:
Construction:
Dynamo type Wattmeter
Dept of E&E ELE101/102 7
Measurement of POWER:
Tdmean α VI cos φ
Since Spring control is used ; Tc α θ
At steady state, Td = Tc
Hence, θ α VI cos φ
Dynamo type Wattmeter
Working: