Introduction to the Method of Measuring Current with a Multimeter
The most critical point to bear in mind when measuring current with a multimeter is not to confuse the current measurement method with the voltage measurement method. Many novices treat current measurement the same way as voltage measurement and connect the test leads in parallel directly to the circuit. If it is an off-brand multimeter, the fuse will blow and the shunt resistor in the current-range shunt assembly will definitely burn out. In the case of a digital multimeter, the meter itself may even be damaged. However, for higher-quality multimeters, if voltage is mistakenly measured under the current range, the voltage signal will be clamped at 0.7 V by bidirectional zener diodes in the current-range protection circuit to protect the current shunt.
To reiterate: for voltage measurement, set the multimeter to the voltage range, insert the red test lead into the VΩ jack and the black lead into the COM jack.
For current measurement, select the appropriate jack according to the magnitude of the current to be measured. For low-current measurement, insert the red lead into the mA jack and the black lead into the COM jack. Connect the red and black test leads in series within the circuit to measure the current. If the display reads "1", it means an overload occurs; you need to switch to a higher range. The mA jack is generally fitted with a 200 mA fuse. For high-current measurement, insert the red lead into the 10 A or 20 A jack and the black lead into the COM jack. Usually, no fuse is provided for the 10 A or 20 A jack.
Pay close attention to the test duration when measuring large currents. The proper measuring time is 10–15 seconds. Prolonged measurement will cause overheating of the constantan or manganin shunt resistors of the current range, resulting in resistance changes and measurement errors.
