Multimeter-Accuracy Tips
The accuracy of a digital multimeter is a combination of systematic and random errors in the measurement results. It indicates the degree of agreement between the measured value and the true value, and also reflects the size of the measurement error. Generally speaking, the higher the accuracy, the smaller the measurement error, and vice versa.
There are three ways to express the accuracy, which are as follows:
Accuracy = ±(a%RDG+b%FS) (2.2.1)
Accuracy = ± (a% RDG + n words) (2.2.2)
Accuracy = ± (a%RDG+b%FS+n words) (2.2.3)
In the formula (2.2.1), RDG is the reading value (that is, the display value), FS represents the full-scale value, and the previous item in the brackets represents the A/D converter and functional converter (such as voltage divider, shunt, true effective value converter), the latter is the error due to digitization.
In the formula (2.2.2), n is the amount of change reflected in the last digit of the quantization error. If the error of n words is converted into a percentage of the full scale, it becomes the formula (2.2.1). Formula (2.2.3) is rather special. Some manufacturers use this expression, and one of the last two items represents the error introduced by other environments or functions.
Digital multimeters are far more accurate than analog analog multimeters. Taking the accuracy index of the basic range for measuring DC voltage as an example, 3 and a half digits can reach ±0.5%, and 4 and a half digits can reach 0.03%.
