Multimeter Measurement Tips
1. Measuring speakers, earphones, dynamic microphones
Use the R×1Ω gear, connect any test pen to one end, and the other test pen to touch the other end, and it will make a clear and loud "click" sound under normal conditions. 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. Estimate the size of the microwave-class capacitor capacity: it can be determined by experience or by referring to the standard capacitor 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. For example, a 100μF/250V capacitor can be estimated by a 100μF/25V capacitor as a reference. As long as the maximum amplitude of their pointer swings is the same, it can be concluded that the capacity is the same.
②. Estimate the capacitance of the picofarad-level capacitor: use the R×10kΩ file, but only the capacitance 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.
3. Measure whether the capacitor is leaking: For capacitors above 1,000 microfarads, you can use the R×10Ω gear to quickly charge it first, and initially estimate the capacitance, then change to the R×1kΩ gear and continue to measure for a while. Should return, but should 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), their leakage characteristics are very demanding, as long as there is a slight leakage, they cannot be used. Then use the R×10kΩ gear to continue the measurement, and the needle should stop at ∞ instead of returning.
3. Check the quality of diodes, triodes, and voltage regulators on the road
In the actual circuit, the bias resistance or diode of the triode, and the peripheral resistance of the Zener tube are generally relatively large, most of which are above hundreds of thousands of ohms, so that the R×10Ω or R×1Ω gear of the multimeter can be used to measure on the road. The quality of the PN junction.
When measuring on the road, use the R×10Ω gear 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 gear to measure). Generally, the forward resistance is at R The needle should indicate about 200Ω when measuring in the ×10Ω gear, and around 30Ω when measuring in the R×1Ω gear (there may be slight differences depending on the phenotype). 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.
For example, when measuring a PN junction with a small resistance value, the forward resistance is too large. If it is soldered down and measured again with the commonly used R×1kΩ file, it may be normal. In fact, the characteristics of this tube have deteriorated and cannot be normal. work or instability.
4. Resistance measurement:
Select the range, the most accurate reading.
Note 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.
