A light indicator which has lower inertia is used to increase the sensitivity of the meter.
- Due to the radial magnetic field and the cylindrical soft-iron core, a linear scale is produced.
- A linear scale is more accurate and easier to be read.
- A mirror is used to prevent parallax error.
- When the observer’s eye is exactly above the indicator, the indicator will cover its own image on the mirror.
- This can be used to prevent parallax error.
Curved Permanent Magnet
- A curved permanent magnet is used to produce a radial field.
- A radial field is a magnetic field where the field lines are either pointing away from or toward the centre of the field.
- A radial can be focused by a cylindrical soft-iron core.
- When a current flows through the coils, a force will be generated due to the interaction between the magnetic field of the permanent magnet and the coil.
- The force will turn the coils, which in turn move the indicator.
Cylindrical Soft-Iron Core
- A cylindrical soft iron core is placed inside the radial field produced by the curved magnet.
- A soft-iron core can focus the magnetic field of the permanent magnet.
- The deflection of the coil and the indicator stops when the force is balanced by the opposing force from the hairspring.
- The angle of deflection is directly proportional to the magnitude of the current in the coil.