How to choose a digital multimeter? A complete collection of digital multimeter selection tips
Digital multimeters are divided into portable and desktop types: portable ones are small in size, light in weight, consume less power, and are suitable for industrial sites; desktop meters have very high accuracy and resolution and are used as standard meters and precision measurements in measurement, scientific research, and production departments. .
When choosing a digital multimeter, you generally consider the following aspects:
1. Function: In addition to the five functions of measuring AC and DC voltage, AC and DC current, resistance and frequency, the current digital multimeter also has recording function, data retention, relative mode, tolerance comparison, diode detection, dBm/dBv Testing, IEEE-488 interface or RS-232 interface and other functions should be selected according to specific requirements when using them.
2. Range and range: The digital multimeter has many ranges, and the basic range has the highest accuracy. Many digital multimeters can select automatic/manual ranges, making measurements convenient, safe and fast. There are also many digital multimeters with over-range capabilities. When the measured value exceeds the range but has not yet reached the maximum display, there is no need to change the range, thereby improving accuracy and resolution.
3. Accuracy: The maximum allowable error of a digital multimeter depends not only on its accuracy, but also on its precision.
4. Input resistance and zero current: If the input resistance of the digital multimeter is too low and 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: When there are various interferences such as electric fields, magnetic fields and various high-frequency noises or when long-distance measurements are made, interference signals are easily mixed in, causing inaccurate readings. Therefore, the measurement should be based on the use environment. Choose an instrument with a high string and common mode rejection ratio. Especially when making high-precision measurements, you should choose a digital multimeter with a protective terminal G, which can suppress common mode interference well.
6. Display form: The display form of the digital multimeter is not limited to numbers, but can also display charts, text and symbols, and some new instruments can also display multiple parameters of the same signal at the same time to facilitate on-site observation, operation and management.
7. Working voltage: The power supply of desktop digital multimeters is generally 220v, while some new digital multimeters have a wide power supply range, which can be between 96v and 264v. Handheld digital multimeter can be used to communicate
There are three forms: battery, rechargeable battery or external battery.
8. Response time, measurement speed, frequency response: The shorter the response time, the better, but some meters have a relatively long response time, and it will take a while for the reading to stabilize; the measurement speed should be based on whether it is used in conjunction with system testing, such as When used in conjunction, speed is very important and must match the entire system; frequency response is appropriately selected based on the measured signal.
9. True RMS measurement: AC voltage measurement is divided into average value conversion, peak value conversion and true RMS conversion. When the waveform distortion is large, the average value conversion and peak value conversion are inaccurate, but the true RMS conversion is not affected by the waveform, making the measurement results more accurate.
10. Resistor wiring method: The resistance measurement wiring method includes four-wire type and two-wire type. When making small resistance and high-precision measurements, you should choose an instrument with four-wire resistance measurement.
