Selecting and Using a Digital Multimeter: Measurement Guidelines
Analog multimeters have relatively low reading accuracy, but the pointer movement is intuitive. Its swinging speed and amplitude can often objectively reflect the magnitude of the measured quantity (such as detecting slight jitter on the TV data bus (SDL) during data transmission). Digital multimeters offer clear direct readings, but the rapid, erratic changes in digits can be difficult to follow visually.
Analog multimeters typically contain two batteries: a 1.5V low-voltage battery and a 9V or 15V high-voltage battery. The black test lead is positive relative to the red lead. Digital multimeters usually use a single 6V or 9V battery. In resistance mode, analog multimeters output much higher current than digital ones. The ×1Ω range can produce a clear "click" sound from a speaker, and the ×10kΩ range can even light up a light-emitting diode (LED).
In voltage mode, analog multimeters have lower internal resistance and lower measurement accuracy. They may even fail to measure accurately in high-voltage, low-current applications because their internal resistance affects the circuit under test (e.g., the measured acceleration voltage of a TV CRT will be much lower than the actual value). Digital multimeters have very high input impedance in voltage mode, at least in the megaohm range, so they exert little influence on the measured circuit. However, their extremely high output impedance makes them susceptible to induced voltages, and readings may be false in environments with strong electromagnetic interference.
In summary, analog multimeters are suitable for measuring high-current, high-voltage analog circuits such as TVs and audio amplifiers. Digital multimeters are better for low-voltage, low-current digital circuits such as pagers and mobile phones. This is not absolute; either type can be chosen based on actual conditions.
