How to use a multimeter to measure circuit voltage, current, resistance, diode, transistor, and field effect tube

1. Voltage measurement
1. DC voltage measurement, such as batteries, walkman power supplies, etc. First, insert the black test lead into the "com" hole and the red test lead into the "V Ω" hole. Select the knob to a range larger than the estimated value (note: the values ​​on the dial are the maximum range, "V-" represents the DC voltage range, "V~" represents the AC voltage range, and "A" represents the current range), and then Connect the test leads to both ends of the power supply or battery; keep the contact stable. The value can be read directly from the display. If it displays "1.", it means that the range is too small, so you need to increase the range before measuring. If "-" appears on the left side of the value, it means that the polarity of the test lead is opposite to the actual power supply polarity. At this time, the red test lead is connected to the negative pole.

2. Measurement of AC voltage. The test lead jack is the same as the DC voltage measurement, but the knob should be turned to the required range at the AC gear "V~". There is no positive or negative distinction between AC voltage, and the measurement method is the same as before. Regardless of whether you are measuring AC or DC voltage, you must pay attention to personal safety and do not touch the metal parts of the test leads with your hands.

2. Current measurement
1. Measurement of DC current. First insert the black test lead into the "COM" hole. If you measure a current greater than 200mA, insert the red test lead into the "10A" jack and turn the knob to the DC "10A" position; if you measure a current less than 200mA, insert the red test lead into the "200mA" jack and turn the knob to a suitable range within DC 200mA. After adjustment, you can start measuring. Insert the multimeter into the circuit, keep it stable, and you can take a reading. If it displays "1.", then the range needs to be increased; if "-" appears on the left side of the value, it means that the current flows from the black test lead into the multimeter.

Measurement of alternating current. The measurement method is the same as 1, but the gear should be set to the AC gear. After the current measurement is completed, the red pen should be inserted back into the "VΩ" hole. If you forget this step and measure the voltage directly, haha! Your watch or power supply will "go up to the sky in a wisp of smoke" - scrapped! 

3. Measurement of resistance
Insert the test leads into the "COM" and "VΩ" holes, turn the knob to the required range in "Ω", and connect the test leads to the metal parts at both ends of the resistor. You can touch the resistor with your hands during measurement , but do not touch both ends of the resistor at the same time, as this will affect the measurement accuracy - the human body is a conductor with high resistance but limited resistance. When reading, keep the test lead and the resistor in good contact; pay attention to the unit: the unit is "Ω" in the "200" gear, the unit is "KΩ" in the "2K" to "200K" gear, and the unit above "2M" is "MΩ".

4. Measurement of diodes
The digital multimeter can measure light-emitting diodes and rectifier diodes... When measuring, the position of the test leads is the same as for voltage measurement. Turn the knob to the "-|>|--" (you will not draw this mark) position; use a red test lead. Connect the positive terminal of the diode and the black test lead to the negative terminal. The forward voltage drop of the diode will be displayed. The voltage drop of Schottky diodes is about 0.2V, that of ordinary silicon rectifiers (1N4000, 1N5400 series, etc.) is about 0.7V, and that of light-emitting diodes is about 1.8~2.3V. Replace the test leads. If the display shows "1.", it is normal, because the reverse resistance of the diode is very large, otherwise the tube has been broken down.

5. The measurement  
pen insertion position of the triode is the same as above; its principle is the same as that of the diode. First assume that pin A is the base, connect the black test lead to this pin, and the red test lead and the other two pins respectively contact the other two pins; if the two readings are both about 0.7V, then use the red pen to connect to pin A and the black pen Touch the other two pins. If both display "1", then pin A is the base. Otherwise, it needs to be measured again, and this tube is a PNP tube. So how to judge the collector and emitter? Digital watches cannot be judged by pointer swing like analog watches, so what should we do? We can use the "hFE" gear to judge: first set the gear to the "hFE" gear, and you can see a row of small jacks next to the gear, which are divided into measurements for PNP and NPN tubes. The tube type has been determined previously. Insert the base into the "b" hole of the corresponding tube type, and insert the other two legs into the "c" and "e" holes respectively. At this time, the value can be read, that is, the β value; then fix the base, and the remaining Swap the two pins; compare the two readings. The position of the pin with the larger reading corresponds to the surface "c" and "e".

Tips: The above method can only directly measure small tubes such as the 9000 series. If you want to measure large tubes, you can use the wiring method, that is, use small wires to lead out the three pins. This is a lot more convenient.

6. Measurement of MOS field effect transistors.
N-channel ones include domestic 3D01, 4D01, and Nissan’s 3SK series. Determination of G pole (gate): Use the diode scale of the multimeter. If the positive and negative voltage drops between a certain pin and the other two pins are both greater than 2V, it will display "1" and this pin is the gate G. Then exchange the test leads to measure the other two pins. When the voltage drop is small, the black test lead is connected to the D pole (drain) and the red test lead is connected to the S pole (source).