What are the technical parameters and measurement methods of digital multimeter?
1, resolution, number of words and bits
Resolution refers to the resolution of small signals when measuring with a multimeter. Knowing the resolution of the multimeter can determine whether it can observe a small change in the measured signal. For example, if the resolution of the digital multimeter is 1mV in the 4V range, it means that it can observe the change of 1mV (1/1000 V) when reading 1V.
If you have to measure the minimum length of 1/4 inch (or 1 mm), then you won't buy a ruler with a minimum scale of 1 inch (or 1 cm). If the normal temperature is 98.6 degrees Fahrenheit, a thermometer that can only measure whole degrees is of little use. You need a thermometer with a resolution of 0.1 degrees.
The words "bit" and "word" are used to describe the resolution of multimeter. They can be grouped according to the number of words or digits displayed by the digital multimeter.
A 3-digit multimeter can display three whole digits (0 to 9) and a "half digit" (only a "1" is displayed or left blank). The display resolution of a 3-digit multimeter is 1,999 words higher. The display resolution of a 4-digit multimeter is as high as 19,999 words. Compared with "bit", using "word" can describe the discrimination rate of multimeter more accurately. The resolution of the current 3-digit multimeter may be as high as 3,200, 4,000 or 6,000 words.
For some measurements, the 3,200-word multimeter can provide better resolution. For example, if a voltage of 200V or higher is to be measured, a 1,999-word multimeter cannot measure 0.1V V.. While a 3,200 multimeter can display 0.1V when measuring the voltage up to 320V. This resolution is the same as that of the more expensive 20,000-word multimeter before the voltage of 320V is exceeded.
2. Accuracy
Accuracy is the maximum permissible error produced under specific operating conditions. In other words, the accuracy indicates how close the measured value displayed by the digital multimeter is to the actual value of the measured signal.
The accuracy of digital multimeter is usually expressed as a percentage of reading. Accuracy is 1% of the reading, and if the displayed reading is 100V, the actual voltage value may be any value between 99V and 101V V..
The technical parameters may also include a bit range added to the basic accuracy parameters. This range represents the number of words that the rightmost digit of the displayed value may change. In this way, the accuracy in the above example can be expressed as "(1%+2)". Therefore, if the displayed reading is 100V, the actual voltage value will be between 98.8V and 101.2V V..
The parameters of analog multimeter are determined by full-scale error, not by the percentage of displayed reading. The typical accuracy of analog multimeter is 2% or 3% of full scale. At 1/10 full scale, the accuracy becomes 20% or 30% of the reading. The typical basic accuracy of digital multimeter is based on the reading between (0.7%+1) and (0.1%+1) or better.
3. Ohm's Law
The voltage, current and resistance of any circuit can be calculated by ohm's law, which states that "voltage equals the product of current and resistance". Therefore, if any two values in this formula are known, the third value can be found.
Digital multimeter uses ohm's law to directly measure and display resistance, current or voltage. The following describes how to use the digital multimeter to measure the required parameters conveniently.
4, digital and analog display
Digital display has high accuracy and resolution, and can display three or more bits for each measured value.
The display accuracy of analog pointer is not high, and the effective resolution is also low, because the value between two tick marks must be estimated.
