How much do you know about the skills of using multimeters
Selection of pointer table and digital table:
1. The reading accuracy of the pointer meter is poor, but the process of the pointer swing is more intuitive, and its swing speed range can sometimes objectively reflect the size of the measured value (such as the slight deviation of the TV data bus (SDL) when transmitting data. jitter); the reading of the digital meter is intuitive, but the process of digital change looks messy and not easy to watch.
2. There are generally two batteries in the pointer meter, one is low voltage 1.5V, the other is high voltage 9V or 15V, and the black test lead is positive terminal relative to the red test lead. Digital meters usually use a 6V or 9V battery. In the resistance mode, the output current of the test pen of the pointer meter is much larger than that of the digital meter. The loudspeaker can make a loud "da" sound with the R×1Ω gear, and the light-emitting diode (LED) can even be lit with the R×10kΩ gear.
3. In the voltage range, the internal resistance of the pointer meter is relatively small compared with the digital meter, and the measurement accuracy is relatively poor. Some occasions with high voltage and micro current cannot even be measured accurately, because its internal resistance will affect the circuit under test (for example, when measuring the acceleration stage voltage of a TV picture tube, the measured value will be much lower than the actual value). The internal resistance of the voltage range of the digital meter is very large, at least in the megohm level, and has little effect on the circuit under test. However, the extremely high output impedance makes it susceptible to the influence of induced voltage, and the measured data may be false in some occasions with strong electromagnetic interference.
4. In short, pointer meters are suitable for the measurement of analog circuits with relatively high current and high voltage, such as TV sets and audio amplifiers. It is suitable for digital meters in the measurement of low-voltage and low-current digital circuits, such as BP machines, mobile phones, etc. Not accurate, you can choose pointer table and digital table according to the situation.
Measuring technique (if no explanation is given, it refers to the pointer table):
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 capacitor of the microwave method: it can be judged according to the maximum amplitude of the pointer swing by experience or referring to the 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 at the R×1kΩ level. 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 depending on the phenotype). 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.
