What principle is used in the operation of an analog meter?

Answer 1

This result can be achieved through various methods. Two most common are:

The electromagnetic principle: the probed quality is converted into current quality and passed through a coil wound around a magnet. That coil is then calibrated to move proportionally to the measured quality, and it thus displaces a gauge overlayed on a scale. For obvious reasons these meters are not well suited for measuring in environments with high (electro)magnetic fields.

The thermal principle: a spiral is constructed using materials that cause the spiral to displace (unwind) due to heat when a current is applied, in proportion to that current, and in turn displaces a needle overlayed on top of a scale. The measured quality is, as above, converted into proportional current. For as well obvious reasons as above, these meters aren't very useful in extreme-temperature conditions (high or low).

Method selection is based on the environment in which the meter will be used, and the measurement accuracy required.

For completeness, pressure-reading gauges oftentimes include a membrane that displaces under pressure in order to move a gauge, but these are not commonly used in electrical circuits (membranes displacing semiconducting material are used instead, to convert pressure change to either voltage change, current change or resistance change, adequately to the requirement).

Answer 2

Analog meters operate on the principle of electromagnetic induction, where a current flowing through a coil creates a magnetic field that interacts with a permanent magnet, causing a needle to move and indicate the measured quantity, such as voltage or current.