Introduction to the Structure of Analog Multimeters
Analog multimeters come in many types, yet they share similar basic structures. An analog multimeter mainly consists of three components: the meter movement, the selector switch, and the measuring circuit.
The meter movement adopts a highly sensitive magnetoelectric mechanism and serves as the display unit for measurement. In essence, it is a sensitive galvanometer. The dial of the meter movement is printed with various symbols, scale lines and values. The symbol A‑V‑Ω indicates that this instrument is a multi‑meter capable of measuring current, voltage and resistance. Multiple scale lines are printed on the dial. Among them, the resistance scale marked "Ω" on the right end has zero on the right and infinity (∞) on the left, with unevenly distributed scale values. The symbol "−" or "DC" stands for direct current, "～" or "AC" for alternating current, and "⊿" denotes the scale shared by AC and DC. Several rows of numbers below the scale lines correspond to different ranges of the selector switch. In addition, the dial bears symbols representing meter parameters, such as DC 20 kΩ/V and AC 9 kΩ/V. A mechanical zero‑adjustment knob (screw) is fitted on the meter movement to calibrate the pointer to the zero position on the left.
The selector switch is used to select the type and range (or multiplier) of the measured electrical quantity. It is a multi‑position rotary switch for choosing measurement functions and ranges (multipliers). Typical measurement functions of a multimeter include: "mA" for DC current, "V" for DC voltage, "V～" for AC voltage, and "Ω" for resistance. Each measurement function is divided into several different ranges (multipliers) for selection.
The measuring circuit converts electrical quantities of different types and magnitudes into DC current acceptable to the meter movement. Figure 1 shows the external view of the MF‑47 multimeter, which can measure multiple electrical quantities including DC current, DC voltage, AC voltage and resistance. When the selector switch is set to the DC current range, it connects to five contact points for DC current measurements at 500 mA, 50 mA, 5 mA, 0.5 mA and 50 μA ranges. Similarly, when switched to the ohm range, resistance can be measured with multipliers of ×1, ×10, ×100, ×1 kΩ and ×10 kΩ. When switched to the DC voltage range, it supports DC voltage measurements for 0.25 V, 1 V, 2.5 V, 10 V, 50 V, 250 V, 500 V and 1000 V. When switched to the AC voltage range, it can measure AC voltage at 10 V, 50 V, 250 V, 500 V and 1000 V ranges.
