Usage Methods and Protective Measures for Multimeters
This article mainly introduces the functions and operating methods of analog multimeters. Analog multimeters feature intuitive pointer indication and fast‑response measurement. Nevertheless, they have low input resistance and relatively large measurement errors. Therefore, they are generally used for measuring variable voltage and current values; users can observe the variation range of voltage and current by watching the swing of the meter pointer.
An analog multimeter mainly consists of a meter movement, measuring‑circuit components and a selector switch. It comes in two form factors: portable and pocket‑size. The dial, zero‑adjustment knobs and test jacks are mounted on the front panel. Although multimeters vary slightly in available functions, they share four fundamental measurement capabilities: DC current measurement, DC voltage measurement, AC voltage measurement, and resistance measurement for both AC and DC circuits. Some models can additionally measure audio level, AC current, capacitance, inductance and specific transistor parameters. Differences in these extra functions bring about variations in physical layout among multimeters.
To measure multiple electrical quantities across various ranges, the measuring circuit converts the measured quantity into DC current acceptable for the magnetoelectric meter movement. The more functions a multimeter offers, the more complicated its measuring circuit becomes. Numerous resistors are built into the circuits for current and‑voltage measurement. Rectifier components are included in the
AC‑voltage measuring circuit, and dry batteries serve as the internal power supply for the resistance‑measuring circuit.
The selector switch of an analog multimeter is a switching component for selecting different measured quantities and measurement ranges. It contains several stationary contacts and moving contacts. Circuits are connected when moving contacts close onto stationary contacts. Stationary contacts are commonly called "throws", while moving contacts are referred to as "poles". When operating the selector switch, poles close onto different throws to establish distinct measuring circuits. The number of poles and throws varies with structural designs. Common selector‑switch configurations for multimeters include four‑pole‑three‑throw, single‑pole‑nine‑throw, and two‑pole‑eleven‑throw types.
