How to express the accuracy of a digital multimeter?
The accuracy of a digital multimeter is the combination of systematic and random errors in the measurement results. It represents the degree of consistency 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 accuracy, 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 equation (2.2.1), RDG is the read value (i.e. display value), FS represents the full-scale value, the first term in parentheses represents the combined error of A/D converters and functional converters (such as voltage dividers, splitters, true RMS converters), and the latter term is the error caused by digital processing. In equation (2.2.2), n is the change in quantization error reflected in the last digit. If the error of n words is converted into a percentage of the full scale, it becomes equation (2.2.1). Equation (2.2.3) is quite unique, as some manufacturers use this expression, with one of the last two terms representing errors introduced by other environments or functions.
The accuracy of a digital multimeter is much better than that of an analog pointer multimeter. Taking the accuracy index of measuring the basic range of DC voltage as an example, it can reach ± 0.5% for 3 and a half bits, 0.03% for 4 and a half bits, etc. For example, OI857 and OI859CF multimeters. The accuracy of a multimeter is an important indicator, which reflects the quality and craftsmanship of the multimeter. A multimeter with poor accuracy is difficult to express its true nature
Value can easily cause measurement errors.
The accuracy depends on the error value included in the measurement. The accuracy specification is expressed as follows: "% of reading+% of range". In this equation, '% of reading' is proportional to the reading, while '% of range' is the offset value. These specifications are developed for each measurement range. If the accuracy does not meet the requirements of measurement resolution, then resolution has no impact on accuracy. However, you can still use a multimeter to monitor small changes during the measurement period. For example, if you want to measure a 10 Vdc signal using a 34401A multimeter with an accuracy of 1 year and a range of 10V, the accuracy is 0.0035+0.0005=10 x (0.0035/100)+10 x (0.0005/100)=+/-0.00040. Therefore, the measurement value is 10.00000, the accuracy is *+/-0.00040, the resolution is 0.00001, and the actual reading is between 9.9996 and 10.0004
