How does a digital multimeter measure current? The principle of digital multimeter measuring current
Method for measuring current with a multimeter
Range selection: The multimeter's DC current range is marked with "mA" and has three ranges: 1mA, 1mA, and 100mA. The range selection should be based on the high current in the circuit.
1. Range selection: The multimeter's DC current range is marked with "mA" and has three ranges: 1mA, 1mA, and 100mA. The range selection should be based on the current magnitude in the circuit. If the current size is unknown, the maximum range should be selected.
2. Measurement method: The multimeter should be connected in series with the circuit being tested. After disconnecting the corresponding part of the circuit, connect the multimeter probe to both ends of the breakpoint. The red probe should be connected to the breakpoint connected to the positive pole of the power supply, and the black probe should be connected to the breakpoint connected to the negative pole of the power supply.
(1) Connect the circuit to make the LED light up normally.
(2) Prepare the multimeter according to the pre use requirements mentioned earlier and place the selector switch in the mA range of 100mA.
(3) Disconnect the middle contact of the potentiometer and the lead between the negative terminal of the LED to form a "breakpoint". At this point, the light-emitting diode goes out.
(4) Connect the multimeter in series at the breakpoint. Connect the red probe to the negative terminal of the LED, and connect the black probe to the middle contact lead of the potentiometer. At this point, the LED lights up again. The scale value indicated by the multimeter pointer is the current value passing through the light-emitting diode.
(5) Correctly read the current value through the light-emitting diode.
Record: The current through the light-emitting diode is xx milliamps.
(6) Rotate the potentiometer handle and observe the changes in the multimeter pointer and the brightness of the light-emitting diode. It can be seen that: Record: The maximum current passing through the light-emitting diode is xx milliamps. The minimum current is xx milliamps.
Through the above operations, we can further understand the role of resistors in circuits.
(7) After the measurement is completed, disconnect the power and store the multimeter as required.
Principle of measuring current with a multimeter
The basic principle of a multimeter is to use a sensitive magneto electric DC ammeter (microampere meter) as the meter head.
When a small current passes through the meter, there will be a current indication. But the meter head cannot pass high currents, so it is necessary to shunt or reduce the voltage by connecting some resistors in parallel or series on the meter head, in order to measure the current, voltage, and resistance in the circuit.
The measurement process of a digital multimeter is converted into a DC voltage signal by a conversion circuit, and then the voltage analog signal is converted into a digital signal by an analog-to-digital (A/D) converter. Then, it is counted by an electronic counter, and finally the measurement result is displayed directly on the display screen in digital form.
