How to choose the right multimeter for you
Digital multimeters must be familiar to all electrical and electronic engineers. A digital multimeter (DMM) is an electronic instrument that must be used in electrical measurements. It can have many special functions, but the main function is to measure electrical parameters such as voltage, current, resistance and on-off. As a modern multi-purpose electronic measuring instrument, it is mainly used in electrical maintenance, equipment maintenance, research and development testing and other application fields. So when choosing a digital multimeter, what key indicators should we consider first?
1. Test principle
There are two principles of digital multimeter testing: the average response and true RMS test methods correspond to different types of electrical signal tests.
For DC signals or standard sine waves, both true RMS and average response instruments can measure accurately; but for signals with distorted waveforms, or typical non-sine waves such as square waves, triangle waves, and sawtooth waves, only True RMS meters can measure accurately.
2. Bandwidth
Bandwidth is the range of AC frequencies that the digital multimeter can respond to within the accuracy range. It is not the function of measuring frequency, but the ability to reflect the AC frequency response. If the frequency of the measured signal exceeds the AC bandwidth of the multimeter, the multimeter will not be able to correctly measure the AC value within the frequency response range.
Example: The range of the test frequency of a digital multimeter is 50KHZ, but the bandwidth is 500HZ. This means that when using this multimeter to test the frequency parameters of the signal, it can reach up to 50KHZ. However, when the frequency of the signal to be tested exceeds 500HZ, if the voltage/current parameters of the signal are tested using the multimeter, the test result will have a large error, so a meter with a suitable bandwidth should be selected to test the corresponding signal.
3. Range
Range refers to the maximum value that the meter can test in the current gear. It is necessary to select the appropriate range according to the range of the measured signal value. Fluke multimeters are all manual/automatic ranges, which is convenient for users to switch freely.
When choosing a digital multimeter, it is necessary to choose a meter with a suitable range according to the actual test needs.
4. Display digits and resolution
Display digits: the range of digits that the multimeter can display.
Usually, the digits that can display all numbers from 0-9 are called integer digits, and the others are collectively called half digits.
For example: the number of display digits of a watch is 3999, only three positions can display all 0-9, and the highest digit can only display 0-3, then it is called a three and a half-digit watch. If the number of display digits is 19999, all 0-9 can be displayed on four positions, and the highest position can only display 0-1, then it is called a four and a half digit table.
Resolution: Describes the smallest change in a physical quantity that can be identified.
The high and low numbers displayed on the half digit of the multimeter and the number of digits displayed by the multimeter determine the resolution of some specific readings. The larger the number of display digits, the higher the resolution of the meter test.
For example: For example, the display digit of Fluke15B+ is 3999, the display digit of Fluke115C is 5999, and the display digit of the higher-level Fluke287C is 49999.
If the actual value of the current measured voltage is 402.6V, Fluke15B+ will display 402V, which can distinguish the change of 1V level signal. Fluke115C will display 402.6V, which can distinguish the change of 0.1V level signal. The Fluke287C will display 402.60V, which can distinguish the change of 0.01V level signal.
5. Other special functions
Other functions such as low-pass filter, dual impedance input, temperature and other auxiliary functions should be reasonably selected according to the actual test requirements and the type of the signal to be tested.
In the selection stage, the appropriate tool should be selected according to the type of the actual signal to be tested and the requirements. Only the most suitable digital multimeter can help you get half the result.
