6 precautions when using a multimeter
A multimeter is a multi-function, multi-range measuring instrument. The following are the issues that should be considered when choosing a multimeter.
1. Function: It should be selected according to specific requirements when using it.
2. Range and range: The digital multimeter has many ranges, but its basic range has the highest accuracy. Many digital multimeters have an automatic range function, which makes the measurement convenient, safe and fast without manual adjustment of the range. 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 allowable error of the digital multimeter depends not only on its variable term error, but also on its fixed term error. When choosing, it also depends on the requirements of stability error and linear error, and whether the resolution meets the requirements. If the general digital multimeter requires grade 0.0005 to 0.002, at least 61 digits should be displayed; 0.005 to 0.01 should have at least 51 digits; 0.02 to 0.05, at least 41 digits should be displayed; 0.1 Below, at least 31 digits should be displayed.
4. Input resistance and zero current: The input resistance of the digital multimeter is too low and the zero current is too high, which 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. Serial mode rejection ratio and common mode rejection ratio: When there are various interferences such as electric field, magnetic field and various high-frequency noises or when performing long-distance measurements, it is easy to mix interference signals, resulting in inaccurate readings, so it should be based on the use environment. Choose an instrument with a high serial-to-common-mode rejection ratio, especially when performing high-precision measurements, you should choose a digital multimeter with 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, texts and symbols to facilitate on-site observation, operation and management. According to the size of its display device, it can be divided into four categories: small, medium, large and super large.
