The Galvanometer
  • A Galvanometer is a device used to measure the magnitude and direction of DC currents.
  • When current is passed through it, the magnetic field of the coil interacts with the magnetic field of the stator.
  • Thus, a force acts on the coil due to the motor effect which causes the needle to deflect and give a reading.
  • To make sure the reading is correct, the following measures are taken:
    • The coil is wrapped around a laminated iron core, which increases sensitivity of the device by preventing flux leakage.
      • This can be many thin sheets of materials packed together to reduce eddy currents which could interfere with the measurement.
    • Curved stators are used to ensure a linear scale
      • This is because a radial magnetic field is created, meaning that it is always parallel with the plane of the coil.
      • From that, torque is maximum and constant ($\tau = nBIA\cos{\theta}$)
    • A counterbalancing spring is to make sure the reading is valid
      • It provides a constant restoring torque, so that when current drops to zero, the pin actually goes back to zero.