How does the multimeter measure the current? The method and principle of the multimeter to measure the current
How to measure current with multimeter
Select the range: the DC current range of the multimeter is marked with "mA", and there are three ranges: 1mA, 1omA, and 100mA. The range should be selected according to the current in the circuit.
1. Select the range: The DC current range of the multimeter is marked with "mA", and there are three ranges: 1mA, 1omA, and 100mA. The range should be selected according to the current 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 under test. After disconnecting the corresponding part of the circuit, connect the multimeter leads to both ends of the breakpoint. The red test lead should be connected to the breakpoint connected to the positive pole of the power supply, and the black test lead should be connected to the breakpoint connected to the negative pole of the power supply.
(1) Connect the circuit so that the light-emitting diodes glow normally.
(2) Prepare the multimeter according to the pre-use requirements mentioned above and set the selection switch to the mA range of 100mA.
(3) Disconnect the lead wire between the middle contact of the potentiometer and the negative electrode of the light-emitting diode to form a "breakpoint". At this time, the LED goes out.
(4) Connect the multimeter in series to the breakpoint. The red test lead is connected to the negative pole of the light-emitting diode, and the black test lead is connected to the middle contact lead of the potentiometer. At this time, the light-emitting diodes light up again. The scale value pointed by the pointer of the multimeter is the current value passing through the LED.
(5) Correctly read the current value through the LED.
Record: The current through the LED is xx mA.
(6) Rotate the handle of the potentiometer to observe the changes of the pointer of the multimeter 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 mA. The minimum current is xx mA.
Through the above operations, we can further understand the role of resistors in the circuit.
(7) After the measurement is completed, disconnect the power supply and put away the multimeter as required.
Multimeter measuring current principle
The basic principle of the multimeter is to use a sensitive magnetoelectric DC ammeter (microampere meter) as the meter head.
When a small current passes through the meter head, there will be a current indication. However, the meter head cannot pass a large current, so some resistors must be connected in parallel or in series on the meter head to shunt or lower the voltage, so as to measure the current, voltage and resistance in the circuit.
The measurement process of the digital multimeter converts the measured value into a DC voltage signal by the conversion circuit, and then converts the voltage analog quantity into a digital quantity by the analog/digital (A/D) converter, then counts through the electronic counter, and finally uses the digital measurement result displayed directly on the display.
When measuring current with a multimeter, you must pay attention to the most important point, do not confuse the method of measuring current with the method of measuring voltage. Because many novices use the same method of measuring current and measuring voltage, and directly connect the test leads into the circuit in parallel, it is easy to cause the fuse to burn out, so everyone must pay special attention when using it.
