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Electronic measuring instruments can be roughly classified into the following categories based on their working principles and uses. 1. Multimeters: Analog voltmeters, analog multimeters (i.e., pointer-type multimeters VOM), digital voltmeters, and digital multimeters (i.e., digital multimeters DMM) all fall into this category. This is a gauge that is used frequently. It can be used to measure AC/DC voltage, AC/DC current, resistance value, capacitor capacitance, inductance, audio level, frequency, and the current gain β of NPN or PNP transistors. 2. Oscilloscope An oscilloscope is an electronic instrument used to measure voltage waveforms; it can display graphically how the voltage signal under test changes over time. Using an oscilloscope not only allows for a clear and intuitive view of the overall changes in the physical quantity being measured, but it also enables the measurement of voltage and current through the waveforms it displays, comparison of frequency and phase, as well as the plotting of characteristic curves. 3. Signal generator: Signal generators (including function generators) provide signal sources for the maintenance and debugging of electronic devices and instruments. It is an oscillator capable of generating a certain waveform, frequency, and amplitude. For example: it can generate sine waves, square waves, triangular waves, ramp waves, and rectangular pulse waves. 4. Transistor Characteristic Plotter A transistor characteristic plotter is a specialized oscilloscope that allows for the direct observation of various transistor characteristic curves and their patterns. For example: the input, output characteristics, and feedback characteristics of transistors in common-emitter, common-base, and common-collector configurations ； Forward and reverse characteristics of diodes ； The voltage-regulating or Zener characteristics of a voltage regulator diode ； It can measure the breakdown voltage, saturation current, β or α parameters of transistors, etc. 5. Megohmmeter A megohmmeter (commonly known as a megger) is a simple, direct-reading instrument used to inspect electrical equipment and measure high resistances; it is typically employed to determine the insulation resistance of circuits, motor windings, cables, etc. Most megohmmeters are powered by a hand-cranked generator, which is why they are called crank meters. Since its scale is in megohms (MΩ), it is called a megohmmeter. 6. Infrared thermometer: An infrared thermometer is a non-contact temperature measurement device that consists of an optical system and electronic circuits; by modulating and linearizing the information, it enables indication, display, and control. The infrared thermometers currently in use fall into two categories: photon-based thermometers and thermal thermometers. They are primarily used for temperature measurement and control in applications such as electric heating furnaces, crops, railway rails, ultra-high voltage cable joints buried deep underground, fire protection, gas analysis, and laser reception. 7. Integrated circuit testers: These instruments can be used to test the functions and parameters of TTL, PMOS, and CMOS digital integrated circuits. They can also determine the model of chips with erased data, as well as perform online function testing and status checking on integrated circuits. 8. LCR parameter tester: a device for measuring inductance, capacitance, and resistance parameters. It can not only automatically determine the properties of components but also display symbolic representations along with their values. It can also measure parameters such as Q, D, Z, Lp, Ls, Cp, Cs, Kp, Ks, etc., and display the equivalent circuit diagram. 9. Spectrum analyzer: Spectrum analyzers are widely used in frequency-domain signal analysis, testing, research, and maintenance. It can simultaneously measure the amplitude and frequency of signals, test multiple signals, and analyze the composition of signals. It can also test the signals of the phone’s logic and RF circuits. For example: control signals for logic circuits, baseband signals, local oscillator signals, intermediate frequency signals, transmission signals, etc., for radio frequency circuits. In addition to the commonly used electronic measuring instruments mentioned above, there are also time meters, bridges, phase meters, dynamic analyzers, optical measuring instruments, strain gauges, flow meters, and more.