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# Method for measuring circuit board parameters by using multimeter and precautions for use Multimeter is also known as multiplex table, multimeter, three-meter, multi-purpose table, etc. It is indispensable for power electronics and other departments >Measurement instruments, generally with the main purpose of measuring voltage, current and resistance. The multimeter is a multi-function, multi-range measuring instrument. The general multimeter can measure DC current, DC voltage, AC current, AC voltage, resistance and audio level, etc., and some can also measure AC current. Capacitance quantity, inductance quantity and some parameters of semiconductor. The multimeter is divided into a pointer multimeter and a digital multimeter according to the display mode.

1, multimeter diode file or resistor file can measure circuit board fault, if using diode file When using the test leads to measure the points to be tested, if the circuit board is short-circuited, it will ring, if there is a indicator on the multimeter >Light, or resistance file,If it is a short circuit, the display of the multimeter is zero.

2. Measurement of DC voltage: First insert the black test pen into the “com” hole and the red test pen into the “V Ω”. The value can be read directly from the display. If the display is “1.”, it means that the range is too small, then it is necessary to add a large amount of time to measure the industrial electrical equipment. Select the knob to a range larger than the estimated value (Note: the values on the dial are the maximum range, “V-” means DC voltage, “V~” means AC voltage, “A” is current), then Connect the meter to the power supply or both ends of the power supply; keep the contact stable. If “-” appears to the left of the value, it indicates that the polarity of the test leads is opposite to the actual power supply polarity. At this time, the red test lead is connected to the negative pole.

3. Measurement of AC voltage: The test lead jack is the same as the DC voltage measurement, but the knob should be switched to the AC position “V~” The required range can be. There is no positive or negative AC voltage, and the measurement method is the same as before. Regardless of the AC or DC voltage, pay attention to personal safety. Do not touch the metal part of the test lead with your hand.

4. Measurement of resistance: turn the range switch > Dial to the appropriate range of Ω, 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 pen is positive and the black test pen is negative, which is the opposite of the analog multimeter. Therefore, when measuring polarized components such as transistors and electrolytic capacitors, attention must be paid to the polarity of the test leads.

5. Measure the current with a multimeter: first select the range, the multimeter’s DC current file has “mA” with 1mA, 1omA, 100mA three-range range. The range selected should be based on the current in the circuit. The multimeter should then be placed in series with the circuit under test. After disconnecting the corresponding part of the circuit, connect the multimeter to the ends of the breakpoint. Finally, the correct reading, the DC current scale is still the second. If the 100mA is selected, the third line can be used, and the reading can be multiplied by 10.

6. Measuring capacitance with a multimeter: Some digital multimeters have the function of measuring capacitance. The range is divided into 2000p, 20n, 200n, 2μ and 20μ. During measurement, the two pins of the discharged capacitor can be directly inserted into the Cx jack on the board, and the display data can be read after selecting the appropriate range.

Precautions for use:

• 1) Before using the multimeter, first perform “Mechanical zeroing”, that is, when there is no measured power, make the multimeter pointer point to zero voltage or zero current.
• 2) In the process of using the multimeter, you can not touch the metal part of the test pen by hand, so as to ensure the accuracy of the measurement on the one hand and personal safety on the other hand.
• 3) When measuring a certain amount of power, you cannot shift gears while measuring, especially when measuring high voltage or high current. Will destroy the multimeter. If you need to shift gears, you should first disconnect the test leads and then measure them after shifting.
• 4) When the multimeter is in use, it must be level Place it to avoid errors. Also, be careful to avoid the influence of external magnetic fields on the multimeter.
• 5) When the multimeter is used, the switch should be placed in the exchange The maximum block of voltage.If it is not used for a long time, the battery inside the multimeter should be taken out to prevent the battery from corroding other devices in the watch.