How to use a digital multimeter: First, you need to understand some basics, such as: power switch, HOLD lock screen button, B/L is generally a backlight, and secondly, you need to understand that the conversion switch V- or DCV is a DC voltage block. It means V~ or ACV. It means AC voltage block. A- or DCA. It means DC current block. A~ or ACA means AC current block. Ω means electrical block. Draw a symbol of a diode. That is the diode block, also called bee. Ringing gear, F represents capacitance gear, H represents inductance gear, hfe represents triode current amplification factor test gear. Generally, a digital meter will have four jacks, namely: VΩ hole, COM hole, mA hole, 10A hole or 20A hole. \r\n\r\nMeasure DC voltage, AC voltage, resistance, capacitance, diode, transistor, check circuit continuity, etc. Insert the red test lead into the VΩ hole and the black test lead into the COM hole. \r\n\r\nTo measure mA level current or μA level current, insert the red test lead into the mA current dedicated jack and the black test lead into the COM hole. \r\n\r\nTo measure the current higher than the mA level, insert the red test lead into the 10A or 20A hole and insert the black test lead into the COM hole. The COM hole is also called the male terminal, which is specially designed to insert the black test lead. \r\n\r\nWhen measuring voltage, choose the range appropriately. If you are measuring DC voltage, you must set the DC voltage level V-(DCV). If you are measuring AC voltage, you must set the AC voltage level V. ~(ACV) Insert the red test lead into the VΩ hole and the black test lead into the COM hole, then connect them in parallel to the circuit to measure the voltage. If you don’t know how big the signal being measured is, choose the maximum range for measurement. When measuring DC, do not consider the positive and negative poles, because the digital meter is not like an analog meter. If the DC signal is measured backwards, the meter needle will move backwards. The digital meter will only display a symbol, indicating that the signal enters from the black test pen. \r\n\r\nWhen measuring current, select the jack according to the size of the current being measured. If you are measuring a small current, insert the red test lead into the mA hole and the black test lead into the COM hole. Insert the red and black test leads into the line to measure the current. If the measurement shows "1", it means that it is over the range, so you need to increase the range measurement. The mA hole is usually equipped with a 200mA fuse. When measuring large currents, insert the red test leads. Insert the black test lead of the 10A or 20A hole into the COM hole. The 10A hole or the 20A hole is generally not designed with insurance. When measuring large currents, you must pay attention to the time. The correct measurement time should be 10-15S. If you measure for a long time, due to the current block Constantan or manganese-copper shunt resistor, overheating will cause resistance changes, causing measurement errors. \r\n\r\nWhen measuring resistance, first hit the electrical barrier with the multimeter and select the appropriate range. If you don’t know the resistance of the resistor being measured, you should select the maximum range, and then insert the red test lead into the black VΩ hole. Insert the test leads into the COM hole and connect them to both ends of the resistor, regardless of the positive and negative poles, because the resistor has no positive and negative poles. If you find that the multimeter displays "1" during the measurement, you need to use the maximum setting to measure it again. If you use the maximum setting to measure the resistance of the resistor, If the value is still "1", it means that the resistor is open circuit. If the resistance value is found to be 001 during the measurement, it means that the resistor has an internal breakdown. When measuring the resistance, first short-circuit the test leads to measure the resistance value of the test lead wires, which is usually 0.1- 0.3Ω, the resistance cannot exceed 0.5Ω. If it exceeds, it means that the 9V battery is caused by the low 9V power supply voltage of the multimeter, or the contact between the cutterhead and the circuit board is loose. Do not hold the metal of the test lead with your hands when measuring. part to avoid entering the human body resistance, which will cause measurement errors. \r\n\r\nWhen measuring a diode, use the diode setting. The open circuit voltage of the VΩ and COM holes of the digital meter diode setting is about 2.8V. Insert the red test lead into the VΩ hole and insert the black test lead into the COM hole. Connect the red test lead to the diode. Positive electrode, black test lead is connected to the negative electrode, and the forward resistance value is measured. On the contrary, the reverse resistance value of the diode is measured, because in the digital meter, the red test lead contacts the positive electrode of the internal battery and is positively charged, while the black test lead contacts the negative electrode of the internal battery and is negatively charged, which is exactly Contrary to the analog watch, the red test lead in the analog watch is electrically blocked from contacting the negative terminal of the internal battery, and the black test lead contacts the positive terminal of the internal battery. If the forward resistance value is 300-600Ω and the reverse resistance value is above 1000, it means the tube is good. If the forward and reverse resistance values ??are both "1", it means the tube is open circuit. If the forward and reverse resistance values ??are both 001, it means the tube is broken. If the forward and reverse resistance values ??are similar, it means the quality of the tube is poor.