Methods and precautions for measuring AC and DC voltages with a multimeter
When measuring AC and DC voltage, first insert the red and black test leads into the VΩ hole and COM hole respectively, and then adjust the range switch to the appropriate position of the AC and DC voltage range according to the type and size of the voltage to be measured to measure the voltage.
The method of measuring the 4V battery voltage with a digital multimeter is shown in the figure above. Adjust the range switch of the multimeter to the DC 20V range, and then touch the positive and negative terminals of the battery with the red and black test leads to read the measured voltage. The 4V battery measured in the picture above is the battery used for rechargeable LED desk lamps. This battery is old, so the displayed voltage is 2.73V.
When measuring DC voltage, since the digital multimeter can automatically display the polarity of the voltage being measured, the red and black test leads can be connected to the positive and negative poles of the battery at will. In the picture above, if the black test lead is connected to the positive terminal of the battery and the red test lead is connected to the negative terminal of the battery, the multimeter will display -2.73V (there may be a slight difference in the positive and negative readings displayed by a few digital multimeters).
By the way, most of today's digital multimeters can only measure the voltage or current of 40-400Hz sine wave alternating current. If the frequency of the measured alternating current is not in the above range or is not a sinusoidal wave, there will be a large measurement error. If you want to accurately measure alternating current with arbitrary waveforms, you can choose a true RMS digital multimeter. The AC-DC conversion circuit in this multimeter is composed of true RMS conversion ICs such as AD736 and AD737, so it can accurately measure AC voltage of arbitrary waveforms.
How to use a multimeter to distinguish between neutral and ground wires
Distinguish between the neutral wire and the ground wire: The ground wire is required to use a yellow/green two-color wire during installation, so it can be distinguished from the color of the wire. The neutral line generally uses a blue line.
1. Set the multimeter range switch to the AC voltage range. All multimeters should have this function.
2. The measuring range is from 200mV to 750V. Generally, the 200V range is selected. Some clamp meters do not have the 200V range, so you can choose a larger range. If the analog multimeter has a smaller range, you can choose 10 V ~ 100V. 3. Then use the red and black test leads to plug in respectively. In V/COM (the jack that usually measures the 220V voltage of home appliances)
3. Wrap the black test lead wire 2-3 times in your left hand. Of course, the more turns the better. Note: Do not touch the metal needle of the black test lead to your hand at this time to prevent electric shock.
4. Take the red test lead in your right hand to measure the neutral line or the live wire respectively. Write down the results of the two measurements. The larger one is the live wire and the smaller one is the neutral wire.
