Basic usage of pointer multimeter
(1) Measurement of DC current
The multimeter generally has three DC current ranges of 1mA, 10mA, and 100mA. The range should be selected according to the current in the circuit. If you don't know the current, you should first select the highest range, and then gradually reduce to the appropriate range.
When measuring DC current, first disconnect the corresponding part of the circuit, and then connect the multimeter pen to both ends of the breakpoint. The red pen is connected to the breakpoint connected to the positive pole of the power supply, and the black pen is connected to the breakpoint connected to the negative pole of the power supply. When reading, the DC current gear should read the value of the second scale line. If the 100mA gear is selected, the third row of numbers under the scale line can be used, and the reading can be multiplied by 10.
(2) Measurement of alternating current
Usually, the multimeter only sets the 1st to 2nd gears for AC current testing, and it is only suitable for measuring low-frequency currents with a large internal resistance of the power supply or a high impedance of the circuit under test, and a frequency below 3kHz. In order not to affect the waveform and working state of the circuit under test, the AC current block of the multimeter must adopt a symmetrical full-wave rectification method.
When measuring, a low-resistance precision sampling resistor is connected in series in the circuit under test, and then the AC voltage block of the multimeter is connected to both ends of the sampling resistor, and the conversion is performed by reading the AC voltage at both ends of the resistor. into the current of the circuit under test.
(3) Measurement of voltage
When measuring AC and DC voltage, you should use the AC voltage block and the DC voltage block respectively, and the selection of the range is the same as the measurement current. When measuring, connect the multimeter to the circuit under test in parallel, connect the red test lead to the circuit under test and the positive pole of the power supply, connect the black test lead to the circuit under test and the negative pole of the power supply, and read out the voltage value.
Note: The scale line of the DC voltage gear is the second scale line. When using 10 gears, the third line of numbers under the scale line can be used to directly read the measured voltage value.
(4) Measurement of resistance
Multimeters generally have five ranges: R×1, R×10, R×100, R×1k, and R×10k. Before measurement, first short-circuit the two test leads, and adjust the "ohm zero adjustment knob" at the same time, so that the pointer just points to the right position of the ohm scale line. In order to ensure accurate measurement, every time the magnification gear is changed, an ohm zero adjustment is required.
When measuring, touch the two test leads to the two ends of the measured resistor, observe the reading of the meter and multiply it by the magnification, which is the resistance value of the measured resistor.
