What are the tips for using a multimeter?
Selection of pointer and number tables:
1. The reading accuracy of pointer meters is poor, but the process of pointer oscillation is relatively intuitive, and the amplitude of its oscillation speed can sometimes objectively reflect the size of the measured object (such as the slight jitter of the TV data bus (SDL) when transmitting data); The reading on the digital meter is intuitive, but the process of numerical changes appears chaotic and difficult to observe.
2. There are usually two batteries inside a pointer meter, one with a low voltage of 1.5V and the other with a high voltage of 9V or 15V. The black probe is the positive terminal relative to the red probe. A 6V or 9V battery is commonly used for digital watches. In the resistance range, the output current of the pointer meter is much larger than that of the digital meter. Using the R × 1 Ω range can make the speaker make a loud "click" sound, and using the R × 10k Ω range can even light up the light-emitting diode (LED).
3. In the voltage range, the internal resistance of the pointer meter is relatively small compared to the digital meter, and the measurement accuracy is relatively poor. In some high-voltage microcurrent situations, it is even impossible to measure accurately because its internal resistance can affect the tested circuit (for example, when measuring the acceleration voltage of a TV cathode ray tube, the measured value may be much lower than the actual value). The internal resistance of the voltage range of a digital meter is very high, at least in the megaohm range, and has little impact on the tested circuit. However, the extremely high output impedance makes it susceptible to the influence of induced voltage, and the data measured in some situations with strong electromagnetic interference may be false.
4. In short, pointer meters are suitable for measuring analog circuits with relatively high current and high voltage, such as televisions and audio amplifiers. Digital meters are suitable for measuring low voltage and low current digital circuits, such as BP machines, mobile phones, etc. It is not absolute, and pointer and number tables can be selected according to the situation.
Measurement skills
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.
