Introduction to the Selection of Digital Multimeters
Digital multimeters dominate the current market. It is wise to choose one according to your actual needs and prioritize product quality. Ordinary users do not need to overemphasize resolution (display digits). Even for applications such as home appliance repair, a basic 3½-digit digital multimeter is sufficient. High-resolution measurements offer no substantial benefits in most scenarios. For most users, a practical and adequate multimeter is enough; there is no need to purchase expensive high-end models. Well-known brands guarantee quality, and mid-range products within most product lines deliver the best cost-performance ratio. Although high-end products have excellent performance, they come with high upfront purchase costs and relatively high ongoing operating expenses.
First, high-performance devices consume more power, leading to higher battery costs. Second, consumable parts such as fuses are costly. For example, a single fuse for a high-end FLUKE multimeter costs more than 60 yuan, so losses caused by one misoperation can be considerable. Third, post-purchase repair costs are related to the grade of the multimeter; premium multimeters incur expensive repair fees.
For users working with high voltage and large current, the safety of the multimeter is more important than measurement accuracy. Generally, high-precision multimeters are suitable for scientific research and R&D applications. Bench multimeters in particular are intended for laboratory use. Ultra-high-precision multimeters of 7½ digits or higher require strict operating specifications, including proper temperature and humidity conditions and periodic metrological calibration. If they are casually stored and powered on for use like ordinary multimeters, they will quickly lose practical value.
From the perspective of measurement technology, there are two methods for measuring AC RMS values with digital multimeters: the average rectification principle and the true RMS principle. The former has lower cost and is mainly suitable for measuring sine waves; readings will be higher when measuring square waves. The latter is relatively complex to implement but provides accurate measurements for various waveforms. Most mid-to-high grade multimeters adopt true RMS measurement. Multimeters with true RMS capability are marked with "True-RMS" on the meter panel, which has become an indicator of the grade of digital multimeters.
Besides measurement accuracy and resolution, another critical specification for multimeter performance is response speed - the time from the start of measurement until the reading stabilizes. It reflects the data processing capability of the multimeter's processor. High-end digital meters feature extremely fast response speeds. Note that this is not directly related to the screen refresh rate of the multimeter. Some users complain about slow measurement speed of their digital multimeters, and this parameter is the cause. Many low and mid-range multimeters omit this specification in their datasheets.
