Working Principle of Electrodynamic or Dynamometer Type Instruments

Working Principle of Electrodynamic or Dynamometer Type Instruments Points : Working Principle of Electrodynamic or Dynamometer Type Instruments, Definition We have the idea of the working principle of the permanent magnet moving coil (PMMC) instrument. Considering how it would behave on a.c. It would have a torque in one direction during one half of the cycle and an equal effect in the opposite direction during the other half of the cycle. If the frequency were very low, the pointer would swing back and forth around the zero point. However, for an ordinary meter, the inertia is so great that on power frequencies the pointer does not go very far in either direction but merely stays (vibrates slightly) around zero. If, however, we were to reverse the direction of the field flux each time the current though the movable coil reverses, the toque would be produced in the same direction for both halves of the cycle. The field can be made reverse simultaneously with the current in the movable coil if the field coil is connected in series with the movable coil. The electrodynamometer mechanism has several pointers resemblance to a series connected motor.