How to measure the on-off of live line with multimeter
In electrotechnics and electric drive, electricity is divided into weak current and strong current, and also into low voltage, high voltage and ultra-high voltage. However, there is strong electricity or even high voltage electricity in weak electricity, such as TV, switching power supply and LED light power supply, which is as weak as several volts and as high as more than 10 thousand volts. There are low-voltage electricity and weak electricity in high voltage, because the control system controls high voltage by low voltage, and weak electricity controls low voltage for safe operation.
I don't approve of simply measuring the on-off of live lines with a multimeter! You can measure whether there is electricity or not with a stylus, or you can use an ohm block to measure the quality of the line after power failure.
Electrician is a high-risk industry, and sometimes it needs to measure data. Without electricity, it is impossible to measure the actual data voltage and current. And waveform diagram. Live measurement belongs to live work. Although there are labor protection articles, insulating gloves and shoes, it is really inconvenient for that guy to bring work. Let's talk about the difficulty of work!
As for how to use the multimeter, you can read the instructions and go to Baidu. Everyone's answers are very good, so I won't repeat them. What I want to express is the precautions for live measurement, how to work safely and use the multimeter safely.
Live measurement of weak current
When measuring, don't blindly measure first. Check the weak current and strong current in the circuit, choose a good gear, and measure the voltage below DC and AC24V. There is basically no danger, but don't touch the commercial power, high voltage parts in the equipment and large capacitors.
When measuring the high voltage in low-voltage equipment, the best way is to cut off the power and discharge (including capacitance) first, then select the gear of the stylus, place the measuring point, and then send electricity to read the measured data. The digital multimeter has a memory button, and you can press the memory button, which will be safer.
When measuring voltage with a multimeter in the factory, the line is not necessarily connected with voltage, and the line is definitely not connected without voltage.
Because it is live measurement, there is a transformer and a motor in the line, and there is electricity at the breakpoint, and there is also electricity at the breakpoint. The electricity at the breakpoint is power supply electricity, and the electricity at the breakpoint is electricity from another phase connected in series through windings or coils. We must pay attention to this phenomenon. Therefore, it is inaccurate to measure the on-off of the line with a multimeter! For commercial power, it should be single-phase electricity. If the live wire is broken, there will be no power supply, but if the neutral wire is broken, the phenomenon that there is electricity and no voltage will be detected.
To sum up, it is correct to measure the on-off of the line with a multimeter. If you don't go around yourself, the best way is to use an ohm block after power failure or use a shaking table to measure the on-off of the line more accurately.
