When using a digital multimeter, you should not only look at the basic specifications, but also look at its features, functions and all design and production indicators.
Here are the basic metrics and performances to consider for a digital multimeter.
(1) Reliability: Especially in harsh conditions, reliability is more important than ever.
(2) Safety: The primary consideration in the design of digital multimeters, especially after independent testing by certified laboratories, and the marking of testing laboratories such as UL, CSA, VDE, etc.
(3) Resolution: Resolution, also known as sensitivity, refers to the smallest quantitative unit of the measurement result of the digital multimeter, that is, the slight change of the measured signal can be seen. For example: If the resolution of the DMM is 1mV in the 4V range, then when measuring a 1V signal, you can see a small change of 1mV. The resolution of a digital multimeter is generally expressed in digits or words.
DMM resolution is an important indicator, just like if you want to measure lengths less than 1mm, you definitely won't use a ruler with the smallest unit in centimeters; or if the temperature is 98.6°F, then it's okay to measure with a thermometer that only has integer marks. To use, you'll need a thermometer with a resolution of 0.1°F.
A 3-and-a-half-digit table, the last three digits can display three full digits from 0 to 9, and the first digit only displays one and a half digits (displaying 1 or no display), that is, a 3-and-a-half-digit table can reach 1999 words resolution; a 4½-digit digital multimeter can achieve a resolution of 19,999 words. The resolution of a digital table is better described in words than in bits. The resolution of today's 3½-digit DMMs has been increased to 3200 or 4000 words. A 3200-word DMM provides better resolution for some measurements. For example, a 1999 word meter, when measuring voltages greater than 200V, you can't display 0.1V. The digital multimeter with 3200 words can still display 0.1V when measuring the voltage of 320V. When the measured voltage is higher than 320V and the resolution of 0.1V is to be achieved, an expensive 20,000-character digital multimeter should be used.
(4) Accuracy: refers to the maximum allowable error that occurs in a specific use environment. In other words, accuracy is used to indicate how close the DMM's measurement is to the actual value of the signal being measured. For digital multimeters, accuracy is usually expressed as a percentage of reading. For example, an accuracy of 1% of reading means that when the DMM shows 100.0V, the actual voltage may be between 99.0V and 101.0V. In the detailed specification, there may be a specific value added to the basic precision, which means the number of words to be added to transform the rightmost end of the display. In the previous example, the accuracy might be marked as ±(1%+2). So if the multimeter reads 100.0V, the actual voltage will be between 98.8V and 101.2V. The accuracy of an analog meter (or analog multimeter) is measured in error over the full scale, not in the displayed reading. The typical accuracy of an analog multimeter is ±2% or ±3% of full scale. The typical basic accuracy of a DMM is between ±(0.7%+1) and ±(0.1%+1) of reading, or even higher.
(5) Ohm's Law: Ohm's law reveals the relationship between voltage, current, and resistance. Applying Ohm's law, any circuit voltage, current, and resistance can be calculated: voltage = current × resistance. So the third value can be calculated by knowing any two values in the formula. A digital multimeter applies Ohm's law to measure and display resistance, current, or voltage.
(6) Digital and analog pointer display: In terms of precision and resolution, digital display has good advantages, and the measured value can be displayed with three or more digits. Analog pointers are slightly inferior in accuracy and resolution, and we generally read by estimating the position of the pointer. The digital multimeter has a bar graph that shows signal changes and trends like an analog pointer, but it is more durable and less damaged.
