How to use a multimeter to measure circuits
Measurement of voltage
1. Measurement of DC voltage, such as batteries, walkman power supplies, etc. Firstly, insert the black probe into the "com" hole and the red probe into the "V Ω" hole. Select the knob to a range larger than the estimated value (note: the values on the dial are all the maximum range, "V -" represents the DC voltage range, "V~" represents the AC voltage range, and "A" is the current range), then connect the probe to the power supply or both ends of the battery; Maintain stable contact. The numerical value can be directly read from the display screen. If it shows "1.", it indicates that the range is too small, so a large range needs to be added before measurement. If a "-" appears to the left of the value, it indicates that the polarity of the probe is opposite to the actual power supply polarity, and the red probe is connected to the negative pole.
2. Measurement of AC voltage. The probe socket is the same as the measurement of DC voltage, but the knob should be turned to the required range at the AC gear "V~". There is no positive or negative distinction in AC voltage, and the measurement method is the same as before. Whether measuring AC or DC voltage, attention should be paid to personal safety and do not touch the metal part of the pen with your hands casually.
Measurement of current
1. Measurement of DC current. First, insert the black pen into the "COM" hole. If measuring a current greater than 200mA, insert the red probe into the "10A" socket and turn the knob to the DC "10A" position; If measuring a current less than 200mA, insert the red probe into the "200mA" socket and turn the knob to the appropriate range within 200mA DC. After adjustment, you can start measuring. Connect the multimeter in series into the circuit and maintain stability to read. If it shows "1.", then the range needs to be increased; If a "-" appears to the left of the value, it indicates that the current flows from the black probe into the multimeter.
2. Measurement of AC 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 "V Ω" hole. If you forget this step and directly measure the voltage, haha! Your watch or power supply will soar into the sky in a wisp of smoke - scrap!
Measurement of resistance
Insert the probe into the "COM" and "V Ω" holes, rotate the knob to the desired range in "Ω", and connect the probe to the metal parts at both ends of the resistor. During measurement, you can touch the resistor with your hand, but do not touch both ends of the resistor with your hand at the same time. This will affect measurement accuracy - the human body is a conductor with high but limited resistance. When reading, it is necessary to maintain good contact between the probe and the resistor; Note the unit: When in the "200" range, the unit is "Ω". When in the "2K" to "200K" range, the unit is "K Ω". Units above "2M" are "M Ω".
Measurement of diodes
A digital multimeter can measure light-emitting diodes, rectifying diodes, etc. When measuring, the probe position is the same as the voltage measurement. Turn the knob to the "- |>| --" position (without drawing this symbol); Connect the red lead to the positive pole of the diode and the black lead to the negative pole. This will display the forward voltage drop of the diode. The voltage drop of Schottky diodes is about 0.2V, while 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. If the probe is replaced and the display screen shows "1.", it is normal because the reverse resistance of the diode is very high, otherwise the tube has been broken down.
Measurement of Transistors
The insertion position of the pen is the same as above; Its principle is the same as that of a diode. Assuming pin A is the base, connect it with a black probe, and the red probe contacts the other two pins separately; If both readings are around 0.7V, then use a red pen to connect pin A and a black pen to contact the other two pins. If both readings show "1", pin A is the base. Otherwise, it needs to be re measured, and this tube is a PNP tube. So how do we determine the collector and emitter? What if a digital meter cannot use the amplitude of the pointer to judge like a pointer meter? We can use the "hFE" gear to determine: first set the gear to the "hFE" gear, and you can see a row of small sockets next to the gear, which are divided into PNP and NPN pipes for measurement. The tube type has already been determined earlier. Insert the base into the corresponding tube type "b" hole, and insert the other two pins into the "c" and "e" holes respectively. At this time, the numerical value can be read, that is β Value; Fix the base again, and switch the other two legs; Compare the two readings, and the pin position with the larger reading corresponds to the surface "c" and "e".
Tip: 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, which is to use small wires to lead out the three pins. This is much more convenient.
Measurement of MOS field-effect transistors
There are domestically produced 3D01, 4D01, and Nissan's 3SK series in the N channel. Determination of G-pole (gate): Use the diode range of a multimeter. If the positive and negative voltage drops between a certain pin and the other two pins are greater than 2V, it shows "1", and this pin is the gate G. Swap the probes again to measure the other two pins. In the case of low voltage drop, the black probe is connected to the D pole (drain), and the red probe is connected to the S pole (source).
