The number of display digits for a digital multimeter is usually 3 1/2-bit ~8 1/2. There are two principles for determining the number of display digits of a digital instrument: one is to show that the number of digits from 0-9 is an integer; the second is that the number of decimal digits is the highest in the maximum display value of the number of molecules, the full scale when the count is 2000, which indicates that the meter has 3 integer digits, and the numerator of the decimal point is 1, the denominator is 2, So called 3 1/2 bits, read "Three bits and a half", its highest bit can only display 0 or 1 (0 usually do not show). 3 2/3 bits (read "Three and two-thirds digits") the highest bit of the digital multimeter can only display 0~2 digits, so the maximum display value is ±2999. In the same case, it is more than 3 1/2 digital multimeter limit of 50%, especially in the measurement of 380V AC voltage is very valuable.
Universal digital multimeter generally belongs to 3 1/2-bit display handheld multimeter, 4 1/2,5 1/2 (6 digits below) Digital multimeter is divided into hand-held, desktop two kinds. Most of the 6 1/2 digits belong to the desktop digital multimeter.
Digital multimeter using advanced technology, display clear and intuitive, reading accurate. It can not only ensure the objectivity of reading, but also accord with people's reading habits, can shorten reading or record time. These advantages are not available in the traditional analog (i.e., pointer) multimeter.
The accuracy of digital multimeter is the synthesis of system error and random error in the measurement results. It indicates the degree of consistency between the measured value and the truth, and also reflects the measurement error size. Generally speaking, the higher the accuracy, the smaller the measurement error, and vice versa.
The accuracy of the digital multimeter is much better than the analog pointer multimeter. Multimeter accuracy is a very important indicator, it reflects the quality of multimeter and process capabilities, the accuracy of the multimeter is difficult to express the true value, easy to cause the miscalculation of the measurement.
Resolving Power (resolution)
Digital multimeter in the lowest voltage range of the last 1 words corresponding to the voltage value, called resolution, it reflects the height of the instrument sensitivity. The resolution of digital instruments increases with the increase of the number of display digits. The highest resolution indices of different digit multimeter can be achieved.
The resolution index of the digital multimeter can also be displayed with the resolutions. Resolution is the percentage of the minimum number (excluding 0) that the meter can display and the maximum number.
It should be pointed out that the resolution and accuracy belong to two different concepts. The former is characterized by the "sensitivity" of the instrument, i.e. the ability to "recognize" the micro voltage, and the latter reflects the "accuracy" of the measurement, i.e. the degree of consistency between the measured result and the truth value. There is no inevitable link between the two, it can not be confused, but also not to the resolution (or resolution) mistaken for the accuracy is similar to the instrument internal A/D converter, the function of the converter has a comprehensive error and quantization error. From the measurement point of view, the resolution is a "virtual" index (independent of the measurement error), accuracy is the "real" indicator (it determines the size of the measurement error). Therefore, any increase in the number of display digits to improve the resolution of the instrument is not achieved.
In multifunction digital multimeter, different functions have their corresponding maximum and minimum value.
The number of measurements measured per second by the digital multimeter is called the measurement rate, and the unit is "secondary/s". It depends largely on the conversion rate of A/D converter. Some hand-held digital multimeter use the measurement cycle to indicate the speed of measurement. The time required to complete a measurement process is called the measurement cycle.
There is a contradiction between the measurement rate and the accuracy index, usually the higher the accuracy and the lower the measurement rate. To resolve this contradiction, you can set different display digits or set the measurement speed switch on the same multimeter: Adding a fast measuring file, which is used to measure A/D converter with a fast rate, and by reducing the number of display digits to greatly improve the measurement rate, this method is more common and can meet the needs of different users for measuring rate.
When measuring voltage, the instrument should have very high input impedance, so that the amount of current that is absorbed from the measured circuit is very few, it will not affect the working state of the circuit or signal source, and can reduce the measurement error.
Measuring the current, the meter should have very low input impedance, so access to the tested circuit, can minimize the impact of the instrument on the circuit, but in the use of multimeter current file, because of the small input impedance, so it is easier to burn out the instrument, please users in the use of attention.