Multimeter: Different Tips for Measuring Different Objects
A multimeter, also known as a volt-ohm meter (VOM), multi-tester, or AVO meter, is an essential measuring instrument in electrical and electronic fields. It is primarily used to measure voltage, current, and resistance. Multimeters are classified into analog (pointer-based) and digital types based on their display. They are versatile, multi-range instruments capable of measuring DC current, DC voltage, AC current, AC voltage, resistance, and audio levels. Some advanced models can also measure capacitance, inductance, and semiconductor parameters (e.g., β).
Measurement Techniques (Unless specified, refers to analog multimeters):
Testing Speakers, Headphones, and Dynamic Microphones:
Use the R×1Ω range. Connect one probe to each terminal of the device. A healthy component should produce a clear, loud "click" sound when probed.
No sound: Indicates a broken coil.
Weak or high-pitched sound: Suggests a coil rubbing issue, rendering the device unusable.
Testing Capacitors:
Select the appropriate resistance range based on capacitance, ensuring the black probe connects to the positive terminal of electrolytic capacitors.
Estimating Microwave-Class Capacitance:
Compare the pointer's maximum swing to a known capacitor of the same value (e.g., a 100μF/250V can be compared to a 100μF/25V). Matching swings indicate similar capacitance.
Estimating Picofarad-Class Capacitance:
Use the R×10kΩ range. For capacitors ≥1000pF, a slight pointer movement indicates sufficient capacitance.
Checking for Leakage:
Large Capacitors (≥1000μF):
Charge briefly on R×10Ω, then switch to R×1kΩ. The pointer should remain near ∞. A return indicates leakage.
Small Timing/Oscillation Capacitors (<几十 μF):
Charge on R×1kΩ, then switch to R×10kΩ. The pointer must stay at ∞ for a non-leaky capacitor.
In-Circuit Testing of Diodes, Transistors, and Zener Diodes:
Use R×10Ω or R×1Ω ranges. Most circuit resistors (e.g., biasing resistors) are large enough (≥hundreds of ohms) to allow reliable PN junction testing.
Expected Readings:
Forward Resistance: ~200Ω on R×10Ω or ~30Ω on R×1Ω (varies by meter).
Reverse Resistance: Near ∞.
Fault Detection:
High forward resistance or low reverse resistance indicates a defective PN junction.
This method quickly identifies faulty components, including those with subtle degradation (e.g., a component testing normal off-circuit but malfunctioning in-circuit due to altered characteristics).
