A multimeter consists of three main components: a meter head, a measurement circuit, and a selector switch.
(1) Meter Head
It is a high-sensitivity permanent-magnet moving-coil DC ammeter, and the main performance indicators of the multimeter are fundamentally determined by the meter head's characteristics. The sensitivity of the meter head refers to the DC current value that flows through it when the pointer deflects to full scale; the smaller this value, the higher the meter head's sensitivity. For voltage measurement, a larger internal resistance indicates better performance. The meter head has four scale lines with the following functions:
First scale (top to bottom): Marked with R or Ω, indicating resistance values. Read this scale when the selector switch is in the ohm range.
Second scale: Marked with ∽ and V/A, indicating AC/DC voltage and DC current values. Read this scale when the selector switch is in the AC/DC voltage or DC current range, and the range is set to any position except AC 10V.
Third scale: Marked with 10V, indicating 10V AC voltage values. Read this scale when the selector switch is in the AC/DC voltage range and the range is set to AC 10V.
Fourth scale: Marked with dB, indicating audio level.
(2) Measurement Circuit
The measurement circuit is used to convert various measured quantities into a small DC current suitable for measurement by the meter head. It consists of resistors, semiconductor components, and battery packs.
It can process different measured quantities (e.g., current, voltage, resistance) and different ranges through a series of treatments (e.g., rectification, current shunting, voltage division) to uniformly convert them into a small DC current within a specific range for measurement by the meter head.
(3) Selector Switch
Its function is to select various measurement circuits to meet the measurement requirements of different types and ranges. The selector switch typically has two parts, each marked with different gear positions and ranges.
