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Cautions for digital multimeter selection

Visits:    Publish Time:2014/6/6 8:40:26

The multimeter by the magnetic measurement system consisting of institutions and rectifiers, multi-range meter mechanical instructions. Can be used to measure AC and DC voltage, AC and DC current, resistance. It also known as a multimeter or complicated meters. Some multimeter can measure capacitance, inductance, which is consisted of mechanism magnetoelectric meter, measured loop and change-over switch. Among them, the switcher is a switching element for measure different functions and different ranges.

As the digital multimeters with high precision, wide measuring range, high measuring speed, small size, strong anti-interference ability and easy to use, and it’s widely used in national defense, scientific research, factories, schools, and measurement testing technology fields, as the specifications are different, the performance indicators are varied, the environment and operation conditions are also different, it’s necessary to choose  right digital multimeter which depend on specific circumstances.

1, Functions

Nowadays, the digital multimeter not only can measure AC and DC voltage, AC and DC current, resistance, but also with numerical calculation, self-test, reading holding, error readout, diode test, word length selection, IEEE-488 interface or RS-232 interface functions, it can be selected by the specific requirements.

2, Accuracy

The maximum allowable error of digital multimeter no only depends on its changeable errors, but also need depend on the fixed-term error. When make a selection, it should see the requirements for stability and linearity, and whether the resolution can meet the requirements. The accuracy requirement for normal Digital Multimeter is class 0.0005 ~ 0.002, with 61 bit digital display at least; for class 0.005 ~ 0.01, with 51 bit digital display at least; for class 0.02 ~ 0.05, with 41 bit digital display at least ; for class0.1, with 31 bit displayed at least.

3, Scope and measure range

There are many measurement ranges in digital multimeter, and the basic range with high precision. Many digital multimeter with automatic range function, make the measurements convenient, safe and fast without manual adjust the range, making . There are many over-range digital multimeter can improve the accuracy and resolution, without change range.

4, The series mode rejection ratio and common mode rejection ratio

When make a long distance measure in electric field, magnetic field with mixed high-frequency noise or interference, it’s easy to sneak into the interference signal, resulting in inaccurate readings, so choose a common mode rejection ratio of the instrument based on operation environment strings, especially for high precision measurements, it should choose a digital multimeter with G protective end, can suppress common mode interference as well.

5, Input resistance and zero current

If the input resistance is too low and zero current of digital multimeter is too high, it will cause measurement errors, the question is to see the allowable limits by measuring device, which depends on the internal resistance value of signal source. It should choose a high input impedance and low zero current instrument, when he signal source impedance is high, this influence is neglected.

6, Response time, measuring speed and frequency range

The response time as short better, which for some meter, the response to relatively long, it need to take a few minutes until the reading is stable. Measurement speed should judge by whether joint with system testing, if used in conjunction, the speed is very important, and the faster the better. The frequency range is selected by the requirement.

7, Display form and power supply

The display form of DMM is not not limited to numbers, but also can be displayed in graphics, text and symbols, for ease of observations, operation and management on-site. According to the dimension, the display device can be divided into small, medium, large and ultra-large.

The common power supply of DMM is 220V, and for some new digital multimeter that with wider power supply range, which between 100V ~ 240V. For some small digital multimeter which equipped with batteries, there are some other digital multimeters is available for AC, internal NiCad battery and external battery.

8, The resistance wiring method

The resistance measurement wiring has four-wire, two-wire system. When measure the small-resistance and high-precision, should choose four-wire resistance measure system.

9, AC voltage conversion form

AC voltage measurement is divided into average value conversion, peak value conversion and RMS conversion. When the waveform in large distortion, the average value conversion and peak value conversion is not accurate, however the rms converter will not affected by waveforms, and can make the measurement results more accurate.

Source:www.whnanrui.com/english