Explain in detail the use and precautions of various functions of the multimeter
DC current file use
Disconnect the measurement point of the required circuit. Specifically, it can be disconnecting the component pins, cutting the copper foil, and soldering the special measurement solder joints, etc. Estimate the value of the measured current (if you are not sure, use the maximum range first), select the appropriate range (the selection of the range is the same as the selection principle of the resistance measurement), connect the red test lead to the current outflow terminal where the original circuit is disconnected, and the black test lead to the current outlet. Disconnected current flows into the terminal. If you are not sure, you can instantly connect the test lead to touch it, and if you find that the pointer is reversed, just replace the test lead for measurement. Note that the test leads cannot be connected in parallel at both ends of the component, otherwise the multimeter will be easily damaged. Then read according to the selected range and pointer deflection position, which is the magnitude of the current flowing through the circuit.
When measuring with a digital multimeter, the screen will display a negative sign after the test leads are reversed.
Another method is to indirectly measure the current of the circuit. Use a multimeter to measure the voltage across the resistor. According to Ohm's law, the current flowing through the resistor can be calculated. Think about it from another angle, if there is no resistance, can you add a current limiting resistor to measure indirectly.
The use of AC current file
It is similar to the DC current block measurement method, except that the test leads do not need to be connected to the circuit with positive and negative polarities for measurement. Read the position of the pointer on the scale line marked with the AC symbol "ac". When it comes to the measurement of the AC current block, it is generally aimed at high-power electrical appliances and equipment. In fact, it is more convenient to measure with a clamp ammeter. It should be noted that the clamp meter can only clamp one of the wires.
Capacitor block use
The pointer multimeter can only roughly detect the quality of the capacitance (it is not suitable to judge the capacitance reduction and open-circuit fault of small-capacity capacitors), and roughly estimate the size of the capacitance, but cannot accurately measure the capacitance. The capacitance of a capacitor usually requires a digital multimeter, a capacitance meter, and a dedicated capacitance measuring instrument to measure.
When using a digital multimeter to measure the capacitance of a capacitor, place the digital multimeter on the capacitance block, select the appropriate range gear according to the capacitance, and insert the capacitor under test directly into the test hole or two times after the capacitor under test is fully discharged. The test leads directly touch the capacitor pins respectively for measurement. The display of the digital multimeter will directly display the capacitance of the capacitor under test.
If the displayed value is equal to or very close to the nominal capacity, it means that the capacitor is normal;
If the displayed capacitance of the capacitor to be tested is much smaller than the nominal capacitance, it means that the capacitance of the capacitor has dropped and can no longer be used.
If the capacitance of the capacitor to be tested exceeds the measurement range of the multimeter and displays 1, then this digital multimeter cannot be used for measurement, and other suitable multimeters or capacitance meters designed for measuring capacitance should be used for measurement.
Diode blocking use
Use a pointer multimeter to measure: generally choose R×100 gear. The red test lead (the negative pole of the battery in the watch) can represent the N pole, and the black test lead can represent the P pole. When the diode is turned on, the pointer points to the on-resistance value of the diode, and the pin connected to the black test pen is the P pole, that is, the positive pole. If the forward and reverse measurement pointers do not swing, the diode has an open circuit; if the forward and reverse measurement resistance values are near 0, it means that the diode is short-circuited; if the pointer also deflects during the reverse measurement, the diode has reverse leakage. The diodes in all three cases are defective and cannot be used further in the circuit.
Use a digital multimeter to measure: the red test lead (the positive pole of the battery in the meter) can represent the P pole, and the black test lead can represent the N pole. The number displayed by the measurement is the forward voltage drop of the diode: 0.5 ~ 0.7V for silicon diodes and 0.15 ~ 0.3V for germanium diodes. If the forward and reverse measurements show "000" or the value is very small, it means that the diode is short-circuited; if both the forward and reverse measurements show 1, it means that the diode is internally open; if the reverse measurement also has a certain voltage value, it means that the diode has reverse leakage .
