Working principle of PMMC:
1. The working principle of PMMC is based on basic meter movement known as D’Arsonval principle stated as when current passes through the coil a deflecting torque is produced due to interaction between magnetic field produced by permanent magnet and magnetic field produced by moving coil.
2. Due to this torque coil deflects and this deflection is proportional to the current flowing through the coil.
3. The pointer attached with coil indicates the magnitude of quantity being measured.
4. Another torque is developed by spring known as controlling torque. This torque helps to stabilize the pointer
5. When controlling torque becomes equal to deflecting torque then pointer attached with scale become stable at equilibrium.