Groupings for digital multimeters
Digital multimeters are classified according to the range conversion method, which can be divided into three types: manual range (MAN RANGZ), automatic range (AUTO RANGZ), automatic/manual range (AUTO/MAN RANGZ).
According to different functions, uses and prices, digital multimeters can be roughly divided into 9 categories: low-end digital multimeters (also known as popular digital multimeters), mid-range digital multimeters, medium/high-end digital multimeters, digital/analog hybrid instruments, digital Instrument with dual display of /analog diagram, multi-purpose oscilloscope (integrating digital multi-meter, digital storage oscilloscope and other kinetic energy into one body).
Test function of digital multimeter
The digital multimeter can not only measure DC voltage (DCV), AC voltage (ACV), DC current (DCA), AC current (ACA), resistance (Ω), diode forward voltage drop (VF), transistor emitter current amplification factor ( hrg), can also measure capacitance (C), conductance (ns), temperature (T), frequency (f), and added a buzzer file (BZ) for checking the continuity of the line, low power method to measure resistance file (L0Ω). Some instruments also have inductance gear, signal gear, AC/DC automatic conversion function, and capacitance gear automatic range conversion function.
Most digital multimeters have added the following novel and practical test functions: reading hold (HOLD), logic test (LOGIC), true effective value (TRMS), relative value measurement (RELΔ), automatic shutdown (AUTO OFF POWER), etc.
Anti-interference ability of digital multimeter
Simple digital multimeters generally adopt the principle of integral A/D conversion. As long as the forward integration time is selected to be exactly equal to the integral multiple of the period of the string interference signal, the string interference can be effectively suppressed. This is because the cross-frame interference signal is averaged out in the forward integration stage. The common frame rejection ratio (CMRR) of middle and low-end digital multimeters can reach 86-120dB.
Development Trend of Digital Multimeter
Integration: The handheld digital multimeter uses a single-chip A/D converter, and the peripheral circuit is relatively simple, requiring only a few auxiliary chips and components. With the advent of dedicated chips for single-chip digital multimeters, a fully functional automatic range digital multimeter can be formed using a single IC, which creates favorable conditions for simplifying design and reducing costs.
