Multimeter Measurement Skills (1)

Multimeter measurement skills (1)
1. Measuring speakers, earphones, and dynamic microphones: use R×1Ω gear, connect one end of any test lead, and touch the other end with the other test lead. Under normal circumstances, a crisp and loud "da" sound will be emitted. If there is no sound, the coil is broken. If the sound is small and sharp, there is a problem of rubbing the coil and it cannot be used.
2. Capacitance measurement: Use the resistance gear, select the appropriate range according to the capacitance capacity, and pay attention to the positive electrode of the capacitor for the black test lead of the electrolytic capacitor during measurement.
① Estimation of the capacity of microwave-grade capacitors: It can be judged by experience or by referring to standard capacitors of the same capacity, according to the maximum amplitude of the pointer swing. The reference capacitors do not have to have the same withstand voltage value, as long as the capacity is the same. It is estimated that a 100μF/250V capacitor can be referenced by a 100μF/25V capacitor. As long as the maximum amplitude of their pointer swings is the same, it can be concluded that the capacity is the same.
② Estimating the capacitance of pico-farad capacitors: R×10kΩ should be used, but only capacitors above 1000pF can be measured. For 1000pF or slightly larger capacitors, as long as the needle swings slightly, it can be considered that the capacity is sufficient.
③Check whether the capacitor is leaking: For capacitors over 1,000 microfarads, you can use R×10Ω to quickly charge it first, and initially estimate the capacity of the capacitor, then change to R×1kΩ and continue to measure for a while. At this time, the pointer should not be Return, but should stop at or very close to ∞, otherwise there will be leakage. For some timing or oscillation capacitors below tens of microfarads, the leakage characteristics are very high. As long as there is a slight leakage, it cannot be used. At this time, you can use the R×10kΩ gear to continue the measurement after charging the R×1kΩ gear. , the same needle should stop at ∞ and should not return.
3. Test the quality of diodes, triodes, and Zener tubes on the road: because in actual circuits, the bias resistors of transistors or diodes, and the peripheral resistance of Zener tubes are generally relatively large, mostly above hundreds of thousands of ohms, so , we can use the R×10Ω or R×1Ω gear of the multimeter to measure the quality of the PN junction on the road. When measuring on the road, use the R×10Ω gear to measure the PN junction should have obvious forward and reverse characteristics. Generally, when the forward resistance is measured in the R×10Ω gear, the needle should indicate about 200Ω, and when the R×1Ω gear is measured, the needle should be The indication is around 30Ω. If the forward resistance value of the measurement result is too large or the reverse resistance value is too small, it means that there is a problem with the PN junction, and there is a problem with the tube. This method is particularly effective for repairs, where bad tubes can be found very quickly, and even tubes that are not completely broken but have deteriorated characteristics can be detected. When you measure the forward resistance of a PN junction with a small resistance value, if you solder it down and use the commonly used R×1kΩ file to test again, it may be normal. In fact, the characteristics of this tube have deteriorated and cannot be Works fine or unstable.
4. Resistance measurement: It is important to choose a good range. When the pointer indicates 1/3 to 2/3 of the full range, the measurement accuracy is the highest and the reading is the most accurate. It should be noted that when using the R×10k resistance gear to measure the large resistance value of the megohm level, do not pinch your fingers at both ends of the resistance, so that the resistance of the human body will make the measurement result small.