The main considerations for choosing a digital multimeter are as follows:
1, Function
In addition to measuring AC and DC voltage, AC and DC current, resistance, frequency, and other five functions, modern digital multimeters also have recording functions, data retention, relative mode, tolerance comparison, diode detection, dBm/dBv testing, IEEE-488 interface or RS-232 interface, and other functions. When using them, they should be selected according to specific requirements.
2, Range and measuring range
The digital multimeter has multiple ranges and high accuracy in basic ranges. Many digital multimeters can have automatic/manual range selection, making measurement convenient, safe, and fast. There are also many digital multimeters that have over range capability. 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
The low input resistance and high zero current of a digital multimeter can cause measurement errors. The key is to determine the limit value allowed by the measuring device, that is, the internal resistance of the signal source. When the impedance of the signal source is high, instruments with high input impedance and low zero current should be selected so that their impact can be ignored.
5, Series mode rejection ratio and common mode rejection ratio
In the presence of various interferences such as electric fields, magnetic fields, and high-frequency noise, or when conducting long-distance measurements, interference signals are easily mixed in, causing inaccurate readings. Therefore, instruments with high serial and common mode rejection ratios should be selected according to the usage environment. Especially for high-precision measurements, a digital multimeter with a protective terminal G should be selected to effectively suppress common mode interference.
6, Display format
The display form of a digital multimeter is not limited to numbers, but can also display charts, text, and symbols. Some new instruments can also display multiple parameters of the same signal simultaneously for on-site observation, operation, and management.
7, Working voltage
The power supply for desktop digital multimeters is generally 220V, while some new types of digital multimeters have a wide power range, which can be between 96V and 264V. Handheld digital multimeters can be in three forms: AC power, rechargeable batteries, or external batteries.
8, Response time, measurement speed, frequency response
The shorter the response time, the better, but some meters have longer response times and need to wait for a period of time before the readings can stabilize; The measurement speed should be based on whether it is used in conjunction with system testing. If used in conjunction, speed is important and must be matched with the entire system; The frequency response should be selected reasonably based on the measured signal.
9, True effective value measurement
AC voltage measurement is divided into average value conversion, peak value conversion, and true effective value conversion. When the waveform distortion is large, the average and peak conversion are inaccurate, while the true effective value conversion is not affected by the waveform, making the measurement results more accurate.
10, Resistance wiring method
There are four wire and two wire wiring methods for resistance measurement. When conducting small resistance and high-precision measurements, instruments with four wire resistance measurement should be selected.
