What are the technical parameters and measurements of a digital meter?
1, resolution, word and bit
Resolution is the ability of a multimeter to discriminate small signals when making measurements. Knowing the resolution of the multimeter, you can determine whether it can observe a very small change in the measured signal. For example, if a digital multimeter has a resolution of 1mV on the 4V scale, it can observe a 1mV (1/1000 V) change when reading 1V.
If you have to measure a minimum length of 1/4 inch (or 1 millimetre), you would not buy a ruler with a minimum scale of 1 inch (or 1 centimetre). If the normal temperature is 98.6 degrees Fahrenheit, a thermometer that only measures whole degrees is not very useful. You need a thermometer with a resolution of 0.1 degree.
The words "bit" and "word" are used to describe the resolution of a multimeter. Digital multimeters can be grouped by the number of words or bits they display.
A 3½-digit multimeter displays three whole digits (0 to 9) and one "half-digit" (only a "1" is displayed or left blank). A 3½ digit multimeter has a display resolution of up to 1,999 words. A 4½-digit multimeter has a display resolution of up to 19,999 words. The use of "words" is a more accurate description of the multimeter's precedence than "digits". Today's 3½-digit multimeters may have resolutions of up to 3,200, 4,000, or 6,000 words.
For some measurements, a 3,200-word multimeter provides better resolution. For example, a 1,999-word multimeter will not measure to 0.1 V if a voltage of 200 V or more is to be measured, whereas a 3,200-word multimeter will show 0.1 V for measurements up to 320 V. This resolution is the same as that of a more expensive 20,000-word multimeter until the voltage exceeds 320 V.
2. Accuracy
Accuracy is the maximum permissible error under certain operating conditions. In other words, accuracy indicates how close the measured value displayed by a digital multimeter is to the actual value of the signal being measured.
The accuracy of a digital multimeter is usually expressed as a percentage of the reading. An accuracy of 1% of the reading means that if the displayed reading is 100V, the actual value of the voltage may be any value between 99V and 101V.
The technical data may also include a bit range added to the basic accuracy parameter. This range represents the number of words by which the rightmost digit of the displayed value may change. Thus, the accuracy in the above example can be expressed as "± (1 % + 2)". Thus, if the display reads 100V, the actual voltage will be between 98.8V and 101.2V.
The parameters of an analogue multimeter are determined by the full scale error, not by a percentage of the displayed reading. Typical accuracy of an analogue multimeter is ±2% or ±3% of full scale. At 1/10 full scale, the accuracy becomes 20% or 30% of the reading. Typical basic accuracy for digital multimeters is based on ± (0.7% + 1) and ± (0.1% + 1) of the reading or better.
