Introduction to Digital MultimetersDigital measuring instruments have become mainstream due to their high sensitivity, accuracy, clear display, strong overload capacity, portability, and ease of use.
▲ Figure 1
Below, we will take this type of digital multimeter as an example to briefly introduce its usage methods and precautions.
02Appearance of Digital Multimeter
03Digital Multimeter Usage Diagram
04Measuring Voltage
1. Insert the black probe into the COM port and the red probe into the VΩ port.
2. Rotate the function switch to V~ (AC), V- (DC), and select the appropriate range.
3. Touch the red probe to the positive terminal of the circuit being tested and the black probe to the ground or negative terminal, which is in parallel with the circuit being tested.
4. Read the number displayed on the LCD screen.
05Measuring Resistance
1. Turn off the circuit power.
2. Select the resistance range (Ω).
3. Insert the black test probe into the COM input socket. Insert the red test probe into the Ω input socket.
4. Connect the probe tips across the two ends of the component or the part of the circuit you want to measure.
5. Check the reading and confirm the measurement unit – ohms (Ω), kilohms (kΩ), or megohms (MΩ).
06Function of Diode Beep Mode
① Judging the Quality of Diodes
Set the dial to the (
) position, insert the red probe into the rightmost hole, and the black probe into the second right hole. Connect the probe tips to the anode and cathode of the diode, then reverse the probes and measure again.
Measurement results are as follows:If the results of the two measurements are: one shows “1” and the other shows a number close to zero. Then this diode is a normal diode; if both measurements are the same, then this diode is damaged. The number displayed on the LCD indicates the forward voltage drop of the diode: about 0.6V for silicon material; about 0.2V for germanium material. Based on the characteristics of the diode, it can be determined that the red probe is connected to the positive terminal of the diode, and the black probe is connected to the negative terminal.
One of the most important characteristics of a diode is:
▲ Unidirectional Conductivity
② Short Circuit Check (Determining Circuit Continuity):
Set the dial to the short circuit ( ) position, with the same probe positions as above. Connect the other ends of the probes to the two points being tested. If these two points are indeed shorted, the multimeter’s buzzer will sound.
07Measuring Current
1. Disconnect the circuit.
2. Insert the black probe into the COM port and the red probe into the mA or 20A port.
3. Rotate the function switch to A~ (AC), A- (DC), and select the appropriate range.
4. Disconnect the circuit being tested, and connect the digital multimeter in series with the circuit being tested. The current in the circuit flows into the red probe from one end, through the multimeter and out of the black probe, then back into the circuit.
5. Turn on the circuit.
6. Read the number displayed on the LCD screen.
08Measuring Capacitance
1. Short-circuit the capacitor terminals to discharge it, ensuring the safety of the digital multimeter.
2. Rotate the function switch to the capacitance (C) measurement range and select the appropriate range.
3. Insert the capacitor into the C-X socket of the multimeter.
4. Read the number displayed on the LCD screen.
Small Knowledge:Capacitance Units:
1F=1000mF=1000uF=1000nF=1000pF
09Precautions for Using Digital Multimeters
1. If the size of the voltage or current to be measured cannot be estimated in advance, first set it to the highest range for measurement, then gradually reduce the range to an appropriate level based on the situation. After measurement, set the range switch to the highest voltage range and turn off the power.
2. When at full scale, the instrument will only display the digit “1” at the highest position, with other positions disappearing. In this case, a higher range should be selected.
3. When measuring voltage, the digital multimeter should be connected in parallel with the circuit being tested. When measuring current, it should be connected in series with the circuit being tested; when measuring DC, the polarity does not need to be considered.
4. When mistakenly using the AC voltage range to measure DC voltage, or mistakenly using the DC voltage range to measure AC voltage, the display will show “000”, or the digits at the lower position will fluctuate.
5. Do not change the range while measuring high voltage (above 220V) or high current (above 0.5A) to prevent arcing and burning the switch contacts.
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