Multimeter: Introduction to Tailored Measurement Techniques for Different Objects
1. Test speakers, headphones, and dynamic microphones: Use R × 1 Ω mode, connect one probe to one end, and touch the other probe to the other end. Under normal circumstances, a crisp "click" sound will be emitted. If it doesn't make a sound, it means the coil is broken. If the sound is small and sharp, it means there is a problem with wiping the coil and it cannot be used.
2. Measure capacitance: Use resistance mode to select the appropriate range according to the capacitance, and pay attention to connecting the black probe of the electrolytic capacitor to the positive electrode of the capacitor during measurement. ① Estimating the capacity of microwave capacitors: It can be determined based on experience or by referring to standard capacitors of the same capacity, based on the maximum amplitude of pointer oscillation. The capacitance referred to does not need to have the same withstand voltage value, as long as the capacitance is the same. For example, estimating a capacitance of 100 μ F/250V can be referenced with a capacitance of 100 μ F/25V. As long as their pointer swings the same maximum amplitude, it can be concluded that the capacitance is the same. ② Estimating the capacitance size of a Pifa level capacitor: It is necessary to use the R × 10k Ω range, but only capacitors above 1000pF can be measured. For capacitors of 1000pF or slightly larger, as long as the pointer swings slightly, it can be considered that the capacity is sufficient. ③ Measure whether the capacitor is leaking: For capacitors above 1000 microfarads, they can be quickly charged using the R × 10 Ω range, and the capacitance can be initially estimated. Then, switch to the R × 1k Ω range and continue measuring for a while. At this point, the pointer should not return, but should stop at or very close to ∞, otherwise there is a leakage phenomenon. For some timing or oscillating capacitors below tens of microfarads (such as oscillating capacitors in color TV switch power supplies), the leakage characteristics are very high. As long as there is a slight leakage, they cannot be used. At this time, they can be charged in the R × 1k Ω range and then switched to the R × 10k Ω range to continue measuring. Similarly, the pointer should stop at ∞ and should not return.
3. In road testing of diodes, transistors, and voltage regulators: Because in actual circuits, the bias resistance of transistors or the peripheral resistance of diodes and voltage regulators are generally large, mostly in the hundreds or thousands of ohms range. Therefore, we can use the R × 10 Ω or R × 1 Ω range of a multimeter to measure the quality of the PN junction on the road. When measuring on the road, the PN junction should have obvious forward and reverse characteristics when measured in the R × 10 Ω range (if the difference in forward and reverse resistance is not significant, the R × 1 Ω range can be used for measurement). Generally, the forward resistance should indicate around 200 Ω when measured in the R × 10 Ω range, and around 30 Ω when measured in the R × 1 Ω range (there may be slight differences depending on different phenotypes). If the measurement result shows that the forward resistance is too high or the reverse resistance is too low, it indicates that there is a problem with the PN junction, and the tube is also problematic. This method is particularly effective for maintenance, as it can quickly identify faulty pipes and even detect pipes that are not completely broken but have deteriorated characteristics. For example, when you measure the forward resistance of a PN junction with a low resistance range and it is too high, if you solder it down and measure it again with the commonly used R × 1k Ω range, it may still be normal. In fact, the characteristics of this tube have deteriorated and it cannot work properly or is unstable.
