How does a digital multimeter measure which hole of the power socket is the live wire
If it is DC, it is very convenient. Just plug the two test leads directly into the two ends of the power supply. If the displayed voltage is positive, the red test lead is positive. If the displayed voltage is negative, the black test lead is positive.
Because alternating current has no positive and negative poles, this method does not apply to alternating current.
So, how do we use a multimeter to distinguish the live wire and neutral wire of AC?
The first method: Now adjust the multimeter to the AC gear (if it is divided into gears, adjust it to a gear greater than 220VAC), and connect the black test lead directly to the ground (you can connect to the hole in the middle of the three-phase socket, if not, you can directly ground it or wall), the red test leads are respectively connected to the neutral wire and live wire socket holes, and the larger number is the live wire.
The second method: Now adjust the multimeter to the AC gear, the black test pen is directly idle, and the red test pen is respectively connected to the neutral wire and the live wire socket hole, and the larger number is the live wire. The voltage measured by this method is not the actual AC voltage, but the neutral wire and live wire can be distinguished.
Of course, if you can’t find the contact point of the neutral wire or the live wire, you don’t need to peel off the insulation layer of the wire. One test lead is grounded, and the other test lead is directly close to the wire insulation layer. The larger reading is the live wire, and the lower reading is is the zero line.
How to use the digital multimeter
(1) How to use the digital multimeter
a Before use, read the relevant instruction manual carefully, and be familiar with the functions of the power switch, range switch, jack, and special jack.
b Turn the power switch to the ON position.
c. Measurement of AC and DC voltage: Turn the range switch to the appropriate range of DCV (direct current) or ACV (alternating current) as required, insert the red test lead into the V/Ω hole, insert the black test lead into the COM hole, and connect the test lead to the circuit under test in parallel. The reading is displayed.
d AC and DC current measurement: set the range switch to the appropriate range of DCA (DC) or ACA (AC), insert the red test lead into the mA hole (at 200mA), insert the black test lead into the COM hole, and connect the multimeter in series to the circuit under test Just in. When measuring DC flow, the digital multimeter can automatically display the polarity.
Measurement of e resistance: Turn the range switch to the appropriate range of Ω, insert the red test lead into the V/Ω hole, and insert the black test lead into the COM hole. If the measured resistance value exceeds the maximum value of the selected range, the multimeter will display "1", and a higher range should be selected at this time. When measuring resistance, the red test lead is positive and the black test lead is negative, which is just the opposite of the pointer multimeter. Therefore, when measuring polar components such as transistors and electrolytic capacitors, you must pay attention to the polarity of the test leads.
