How to Choose a Multimeter Suitable for Your Use
The performance of a multimeter mainly covers five aspects: measurement accuracy, extended functions, reliability, durability and product safety characteristics.
Multimeter accuracy consists of two parts: one is measuring accuracy, commonly referred to as "error"; the other is measurement resolution, known as the "digit count of the multimeter". There is no necessary correlation between the measurement resolution and measurement accuracy of a multimeter. Although products with high measurement resolution are generally considered higher-grade and tend to deliver good measuring accuracy, this is not always the case.
Some manufacturers take shortcuts. Their products appear to have more display digits and abundant functions, yet due to cost and technical constraints, they cannot properly control accuracy and stability. It is entirely possible that a 3½-digit multimeter achieves better measurement accuracy than a seemingly 4½-digit meter. The resolution of a multimeter must be based on accuracy; otherwise, the high-digit readout has no practical measurement value. High-precision measurement tasks impose strict requirements on multimeter accuracy, which is one of the key indicators for evaluating product grade.
The measurement accuracy of a multimeter gradually degrades over time. This is the primary reason why instruments require periodic metrological calibration. Highly reliable multimeters feature long service life and strong resistance to harsh external environments. Factors causing increased measurement errors fall into internal and external categories. External factors include operating environment and usage frequency: high and low temperatures and high humidity affect component characteristics. Wear and aging are inevitable as usage time and cycles accumulate. Internal factors relate to product quality, ranging from circuit design and fabrication to component selection and manufacturing processes. Components with identical functions are available in two grades: expensive ones with low temperature coefficients, excellent performance and long service life, and low-cost ones with mediocre performance. The grade of selected components directly affects product cost, and manufacturers of different brands make different trade-offs.
Brands targeting the high-end market select high-stability components and designs following the principle of premium quality at a premium price, ensuring product reliability and durability. Although priced higher, these products offer stable performance, long service life and low repair rates. Brands competing purely on price strictly control costs, even cutting corners. Such products are cheap, and defects may not be obvious in the early stage of use, but problems will gradually emerge as time goes by. Fortunately, most casual users are not sensitive to multimeter accuracy and lack metrological tools. For them, reading 1.5xx V when testing dry batteries and 22x V for mains AC voltage is sufficient. That explains why many users claim their inexpensive multimeters work fine and have lasted for years. In fact, many of these meters are already out of specification once formally calibrated.
