9 Reasons to Choose a Digital Multimeter
Due to its high accuracy, wide measurement range, fast measurement speed, small size, strong anti-interference ability, and convenient use, digital multimeters are widely used in technical fields such as national defense, scientific research, factories, schools, and measurement testing, but their specifications are different. , There are a variety of performance indicators, and the use environment and working conditions are also different. Therefore, the appropriate digital multimeter should be selected according to the specific situation.
The selection of a digital multimeter is generally considered from the following aspects:
(1) Function:
In addition to the five functions of measuring AC and DC voltage, AC and DC current, and resistance, the digital multimeter also has digital calculation, self-test, reading hold, error readout, diode detection, word length selection, IEE-488 interface or RS Functions such as -232 interface should be selected according to specific requirements.
(2) Range and range:
Digital multimeters have many ranges, but the basic range is the most accurate. Many digital multimeters have automatic range function, no need to manually adjust the range, making the measurement convenient, safe and fast. There are also many digital multimeters with over-range capability. When the measured value exceeds the range but has not reached the maximum display, it is not necessary to change the range, thereby improving the accuracy and resolution.
(3) Accuracy:
The maximum error allowed by a digital multimeter depends not only on its variable error, but also on its fixed error. When choosing, it also depends on the requirements of stability error and linearity error, and whether the resolution meets the requirements. If a general digital multimeter requires 0.000 5 to 0.002, at least 6 and a half digits should be displayed; 0.005 to 0.01, at least 5 and a half digits should be displayed; 0.02 to 0.05, at least 4 and a half digits should be displayed ; Below level 0.1, there should be at least 3 and a half digits displayed.
(4) Input resistance and zero current:
If the input resistance of the digital multimeter is too low or the zero current is too high, it will cause measurement errors. The key depends on the limit value allowed by the measuring device, that is, the internal resistance of the signal source. When the signal source impedance is high, an instrument with high input impedance and low zero current should be selected so that its influence can be ignored.
(5) Series mode rejection ratio and common mode rejection ratio:
In the presence of various disturbances such as electric fields, magnetic fields and various high-frequency noises or long-distance measurements, it is easy to mix in interference signals, resulting in inaccurate readings. Therefore, instruments with high string and common-mode rejection ratios should be selected according to the use environment. Especially when performing high-precision measurements, you should choose a digital multimeter with a protection terminal G, which can well suppress common-mode interference.
(6) Display form and power supply:
The display form of the digital multimeter is not limited to numbers, but can also display charts, text and symbols, so as to facilitate on-site observation, operation and management. According to the dimensions of its display devices, it can be divided into four categories: small, medium, large and super large.
The power supply of a digital multimeter is generally 220 V, and some new digital multimeters have a wide power supply range, which can be between 100 and 240 V. Some small digital multimeters can be used with batteries, and some digital multimeters can be used in three ways: alternating current, internal nickel-cadmium batteries or external batteries.
(7) Response time, measurement speed, frequency range:
The shorter the response time, the better, but the response time of some meters is relatively long, and the reading can be stabilized after a period of time. The measurement speed should be based on whether it is used in combination with the system test. If it is used in combination, the speed is very important, and the faster the better. The frequency range can be appropriately selected according to the needs.
(8) AC voltage conversion form:
AC voltage measurement is divided into average value conversion, peak value conversion and effective value conversion. When the waveform distortion is large, the average value conversion and peak value conversion are not accurate, but the effective value conversion can not be affected by the waveform, so that the measurement results are more accurate.
(9) Resistance wiring method:
There are four-wire system and two-wire system for resistance measurement wiring. When performing small resistance and high-precision measurement, the resistance measurement wiring method with four-wire system should be selected.
With the development of large-scale integrated circuits and display technology, digital multimeters are gradually developing in the direction of miniaturization, low power consumption, and low cost. Digital multimeters are also clearly divided into portable and desktop. Portable is generally 3 and a half or 4 and a half digits, small in size, light in weight, and consumes less power, suitable for production workshops or field use; desktop can reach 6 and a half or 7 and a half digits, and its accuracy and resolution are getting higher and higher. Microprocessor and GPIP interface equipment, used as standard meter and precision measurement in measurement, scientific research and production departments.
