What issues should be considered when choosing a multimeter?
The multimeter is a multi-functional, multi-range measuring instrument. Let's talk about the issues that should be considered when choosing a multimeter.
1. Function: It should be selected according to specific requirements when using.
2. Range and range: The digital multimeter has many ranges, but its basic range has the highest accuracy. 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 item errors, but also on its fixed item errors. When choosing, it also depends on the requirements of stability error and linearity error, and whether the resolution meets the requirements. If the general digital multimeter requires 0.0005 to 0.002, at least 61 digits should be displayed; 0.005 to 0.01, at least 51 digits should be displayed; 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: 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 measurement 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: In the presence of various interferences 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, so it should be adjusted according to the use environment Choose an instrument with a high string and common-mode rejection ratio, 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.
