Other Measuring Techniques for Multimeters
1. Test speakers, earphones, and dynamic microphones: use the R×1Ω gear, connect any test lead to one end, and the other test lead to touch the other end. It will make a crisp "da" sound under normal conditions. If there is no sound, the coil is broken. If the sound is small and sharp, there is a problem with the ring rubbing, and it cannot be used.
2. Capacitance measurement: use the resistance file, select the appropriate range according to the capacitance capacity, and pay attention to the black test lead of the electrolytic capacitor should be connected to the positive pole of the capacitor when measuring.
①. Estimate the size of the microwave-grade capacitor capacity: it can be judged according to the maximum amplitude of the pointer swing based on experience or referring to a standard capacitor of the same capacity. The referenced capacitors do not need to withstand the same voltage value, as long as the capacity is the same, for example, a 100μF/250V capacitor can be used as a reference for a 100μF/25V capacitor, as long as their pointers swing to the same extent, it can be concluded that the capacity is the same .
②. Estimate the capacitance of picofarad capacitors: R×10kΩ should be used, but only capacitance above 1000pF can be measured. For a capacitance of 1000pF or slightly larger, as long as the hands of the watch swing slightly, the capacity can be considered sufficient.
③. To measure whether the capacitor is leaking: for a capacitor above 1,000 microfarads, you can first use the R×10Ω file to quickly charge it, and initially estimate the capacitor capacity, and then change to the R×1kΩ file to continue measuring for a while. At this time, the pointer does not It should return, but stop at or very close to ∞, otherwise there will be leakage. For some timing or oscillating capacitors below tens of microfarads (such as the oscillating capacitors of color TV switching power supplies), the requirements for their 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×1kΩ range. Then use the R×10kΩ file to continue the measurement, and the hands 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 resistance of triodes or the surrounding resistance of diodes and Zener tubes are generally relatively large, mostly in hundreds or thousands of ohms. , we can use the R×10Ω or R×1Ω file of the multimeter to measure the quality of the PN junction on the road. When measuring on the road, use the R×10Ω file to measure the PN junction should have obvious forward and reverse characteristics (if the difference between the forward and reverse resistance is not obvious, you can use the R×1Ω file to measure), generally the forward resistance is at R The hands should indicate about 200Ω when measuring in the ×10Ω range, and about 30Ω when measuring in the R×1Ω range (there may be slight differences according to different phenotypes). If the measurement result shows that the forward resistance is too large or the reverse resistance is too small, it means that there is a problem with the PN junction, and there is also a problem with the tube. This method is particularly effective for maintenance, and can find out bad pipes very quickly, and even detect pipes that have not completely broken but whose characteristics have deteriorated. For example, when you use a small resistance file to measure the forward resistance of a certain PN junction is too large, if you solder it down and use a commonly used R×1kΩ file to measure it, it may still be normal. In fact, the characteristics of this tube have deteriorated. Not working or unstable anymore.
4. Measuring resistance: It is important to select a good range. When the pointer indicates 1/3 to 2/3 of the full scale, the measurement accuracy is the highest and the reading is the most accurate. It should be noted that when using the R×10k resistance file to measure a large resistance of 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 smaller.
