Skills of digital multimeter measurement
1. Voltage measurement
1. Measurement of DC voltage, such as battery, Walkman power supply, etc. First insert the black test lead into the "com" hole, and the red test lead into the "V Ω". Select the knob to a range larger than the estimated value (note: the values on the dial are the maximum range, "V-" indicates the DC voltage range, "V~" indicates the AC voltage range, and "A" is the current range), and then turn the Connect the test lead to the power supply or both ends of the battery; keep the contact stable. The value can be read directly from the display screen, if it is displayed as "1.", it indicates that the measuring range is too small, so it is necessary to increase the measuring range before measuring. If "-" appears on the left side of the value, it means that the polarity of the test lead is opposite to that of the actual power supply. 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 measurement of DC voltage, but the knob should be turned to the required range at the AC gear "V~". There is no difference between positive and negative AC voltage, and the measurement method is the same as before. Regardless of measuring AC or DC voltage, pay attention to personal safety, and do not touch the metal part of the test lead with your hands.
2. Current measurement
1. Measurement of DC current. First insert the black test lead into the "COM" hole. If measuring a current greater than 200mA, insert the red test lead into the "10A" jack and turn the knob to DC "10A"; if measuring 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. Once adjusted, it's time to measure. String the multimeter into the circuit, keep it stable, and you can read it. If it is displayed as "1.", then increase the range; 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 directly measure the voltage, haha! Your watch or power supply will "go up into the sky in a wisp of smoke" - scrapped!
3. Resistance measurement
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 resistance. During the measurement, you can touch the resistance with your hands, but do not use your hands at the same time. Contact both ends of the resistance, which will affect the measurement accuracy - the human body is a conductor with great resistance but finite size. When reading, keep the test lead and the resistor in good contact; pay attention to the unit: the unit is "Ω" in the "200" range, "KΩ" in the "2K" to "200K" range, and the unit above "2M" is "MΩ".
Fourth, the measurement of the diode
The digital multimeter can measure light-emitting diodes, rectifier diodes... When measuring, the position of the test leads is the same as that of the voltage measurement, turn the knob to the -||-- (cannot draw this mark) position; connect the positive pole of the diode with the red test lead, and connect the black test lead to the Negative, the forward voltage drop of the diode will be displayed. The voltage drop of the Schottky diode is about 0.2V, the common silicon rectifier (1N4000, 1N5400 series, etc.) is about 0.7V, and the light-emitting diode 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.
For the pointer multimeter, the red test lead is connected to the negative pole of the battery, and the black test lead is connected to the positive pole of the battery. Therefore, when using a pointer meter to measure the diode, if the resistance is small, the end of the black test lead is the positive pole; One end of the test lead is negative.
For a digital multimeter, if the resistance is small, the red test lead is positive; if the resistance is large, the black test lead is positive.
Five, the measurement of the triode
The insertion of the test leads is the same as above; the principle is the same as that of a diode. First assume that pin A is the base, connect the pin with a black pen, and touch the other two pins with the red pen; if the two readings are about 0.7V, then connect the pin with a red pen, black pen Touch the other two pins, if both display 1, then the A pin is the base, otherwise it needs to be re-measured, and this tube is a PNP tube. So how to judge the collector and emitter? The digital meter cannot be judged by the swing of the pointer like the pointer meter, so what should we do? We can use the "hFE" gear to judge: firstly switch the gear to the "hFE" gear, and you can see that there is a row of small jacks next to the gear, which are divided into PNP and NPN tube measurements.
The tube type has been judged before, 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 rest Swap the two pins; compare the two readings, the position of the pin with the larger reading corresponds to the surface "c" and "e".
Tip: The above method can only directly measure small tubes such as 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 much more convenient.
6. Measurement of MOS field effect tube
The N-channel has domestic 3D01, 4D01, and Nissan's 3SK series. Determination of G pole (gate): use the diode file of the multimeter. If the positive and negative voltage drops between one pin and the other two pins are greater than 2V, it will display "1", and this pin is grid G. Then exchange the test leads to measure the other two feet. In the case of the small voltage drop, the black test lead is connected to the D pole (drain), and the red test lead is connected to the S pole (source).
