Using a multimeter to troubleshoot short-circuit faults on a circuit board.
Both the diode range and the resistance range of the multimeter can be used to detect faults in the circuit board. When using the diode range, use the test leads to measure the points to be tested. If the circuit board is short-circuited, the multimeter will beep. For some multimeters with indicator lights, if using the resistance range, when there is a short-circuit, the display of the multimeter will show zero.
The multimeter is also known as a multifunction meter, multipurpose meter, three-purpose meter, or versatile meter. It is an indispensable measuring instrument in departments such as power electronics. Generally, it is mainly used for measuring voltage, current, and resistance. The multimeter is a multifunctional and multi-range measuring instrument. Generally, a multimeter can measure DC current, DC voltage, AC current, AC voltage, resistance, and audio level, etc. Some multimeters can also measure AC current, capacitance, inductance, and some parameters of semiconductors. According to the display method, multimeters are divided into pointer multimeters and digital multimeters.
Measurement of DC voltage: First, insert the black test lead into the "com" hole and the red test lead into the "V Ω" hole. The value can be directly read from the display screen. If the display shows "1.", it indicates that the range is too small, and the range should be increased before measuring industrial electrical appliances. Select a range larger than the estimated value (Note: The values on the dial are all maximum ranges. "V-" represents the DC voltage range, "V～" represents the AC voltage range, and "A" is the current range). Then connect the test leads to the power supply or both ends of the power supply and keep the contact stable. If a "-" appears on the left side of the value, it indicates that the polarity of the test leads is opposite to the actual polarity of the power supply, and at this time, the red test lead is connected to the negative pole.
Measurement of AC voltage: The insertion of the test lead jacks is the same as that for measuring DC voltage, but the knob should be turned to the AC range "V～" at the required range. There is no positive or negative distinction for AC voltage, and the measurement method is the same as described above. Whether measuring AC or DC voltage, pay attention to personal safety and do not touch the metal part of the test leads casually.
Measurement of resistance: Turn the range switch to the appropriate Ω range, insert the red test lead into the V/Ω hole, and insert the black test lead into the COM hole. If the measured resistance value exceeds the maximum value of the selected range, the multimeter will display.1. At this time, a higher range should be selected. When measuring resistance, the red test lead is the positive pole and the black test lead is the negative pole, which is exactly the opposite of the pointer multimeter. Therefore, when measuring polar components such as transistors and electrolytic capacitors, pay attention to the polarity of the test leads.
Measuring current with a multimeter: First, select the range. The DC current range of the multimeter is marked with "mA" and has three ranges: 1mA, 10mA, and 100mA. Select the range according to the magnitude of the current in the circuit. Then the multimeter should be connected in series with the circuit under test. After disconnecting the corresponding part of the circuit, connect the test leads of the multimeter to both ends of the break point. Finally, read the value correctly. The scale of the DC current range is still the second one. When selecting the 100mA range, the third row of numbers can be used, and the reading should be multiplied by 10.
Measuring capacitance with a multimeter: Some digital multimeters have the function of measuring capacitance, and its ranges are divided into five levels: 2000p, 20n, 200n, 2μ, and 20μ. When measuring, directly insert the two leads of the discharged capacitor into the Cx jack on the meter panel. After selecting an appropriate range, the displayed data can be read.
