☞ This is the 15470th article published by Metal Processing (mw1950pub)

Editor’s Note

A multimeter is a multifunctional and multi-range measuring instrument. Generally, a multimeter can measure direct current, direct voltage, alternating current, alternating voltage, resistance, and audio levels. Some can also measure alternating current, capacitance, inductance, and certain parameters of semiconductors. Multimeters are classified into analog and digital types based on their display methods.

1Introduction to Digital MultimetersDigital measuring instruments have become mainstream due to their high sensitivity, accuracy, clear display, strong overload capability, portability, and ease of use.Below, we will use this model of digital multimeter as an example to briefly introduce its usage and precautions.2Appearance of the Digital Multimeter3Illustration of Digital Multimeter Usage4Measuring Voltage1. 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 under test and the black probe to the ground or negative terminal, i.e., connect in parallel with the circuit.4. Read the digital display on the LCD.5Measuring 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 the resistance of.

5. Check the reading and confirm the measurement unit – ohms (Ω), kilohms (kΩ), or megohms (MΩ).

6Function of the Diode Buzzer Range

① Judging the condition of a diode: Set the dial to ( ) range, insert the red probe into the rightmost hole, and the black probe into the second hole from the right. Connect the probe tips to the two terminals of the diode, as shown below, and then reverse the probes to measure again.

The 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 show the same result, then this diode is damaged. The number displayed on the LCD is the forward voltage drop of the diode: about 0.6V for silicon; about 0.2V for germanium. Based on the characteristics of the diode, it can be determined that the red probe is connected to the positive terminal of the diode, while the black probe is connected to the negative terminal.

The most important characteristic of a diode is:

Unidirectional Conductivity

② Short circuit check (determining continuity):

Set the dial to the short circuit ( ) range, with the same probe positions as above. Use the other ends of the probes to connect to the two points being tested. If these two points are indeed shorted, the buzzer in the multimeter will sound.

7Measuring 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 under test, and connect the digital multimeter in series with the circuit. The current from one end of the circuit flows into the red probe and exits through the black probe back into the circuit;

5. Reconnect the circuit;

6. Read the digital display on the LCD.

8Measuring Capacitance

1. Short-circuit the capacitor’s 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.

Small Knowledge: Unit of capacitance:

1F=1000mF=1000uF=1000nF=1000pF

9Precautions for Using the Digital Multimeter

1. If the size of the voltage or current to be measured cannot be estimated in advance, first set it to the highest range and measure once, then gradually reduce the range to an appropriate position based on the situation. After measurement, set the range switch to the highest voltage position and turn off the power.

2. When at full scale, the instrument will only display the digit “1” at the highest position, and other positions will disappear. At this time, a higher range should be selected.

3. When measuring voltage, the digital multimeter should be connected in parallel with the circuit under test. When measuring current, it should be connected in series with the circuit under test, and polarity does not need to be considered when measuring DC.

4. If the AC voltage range is mistakenly used to measure DC voltage, or the DC voltage range is mistakenly used to measure AC voltage, the display will show “000”, or the numbers on the lower positions will fluctuate.

5. It is prohibited to 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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☞ Source: Jicheng Training ☞This article was edited by: Jacy ☞ Media cooperation: 010-88379790-801 ☞The only submission website for Metal Processing Magazine: http://tougao.mw1950.cn/

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