Instruments Types of Instruments Permanent Magnet Moving Coil PMMC O...

INSTRUMENTS -- ESSENTIALS OF INDICATING INSTRUMENTS -- PERMANENT MAGNET MOVING COIL (PMMC)


Types of Instruments:
1) Absolute Instruments
2) Secondary Instruments
3) Indicating Instruments
4) Integrating Instruments
5) Recording Instruments
Essentials of Indicating Instruments:
1) Deflecting Torque
2) Controlling Torque
3) Damping Torque

PERMANENT MAGNET MOVING COIL INSTRUMENT:
PRINCIPLE: When a current carrying conductor is placed in a magnetic field, it experiences a force. The direction of force is given by Fleming's left hand rule.

Dynamometer Type Instruments, Electrical Engineering Dynamometer Type In...

ELECTRODYNAMIC OR DYNAMOMETER TYPE INSTRUMENTS

It is very similar to PMMC instruments except that the permanent magnet field is replaced by coils (usually 2 fixed air cored coils) which carry current to be measured. The coils are usually air cored to avoid hysteresis, eddy currents and other errors.
Deflecting torque is produced by interaction of magnetic fields. One field is due to current in fixed coil and other field is due to current in moving coil.