Procedures for DC Current Measurement with a Multimeter
① Mechanical Zero Adjustment Just like resistance and voltage measurement, perform mechanical zero‑adjustment on the multimeter before use. The operation is identical to that for resistance and voltage measurement described above and will not be repeated here. For frequently‑used multimeters, mechanical zero‑adjustment is not required before every measurement.
② Range Selection Estimate the approximate DC current value according to the power supply in the circuit under test and select an appropriate range. If the current magnitude is unknown, start with the maximum current range (500 mA). Gradually switch to lower‑current ranges until a suitable one is found. The selection criterion is the same as that for voltage measurement.
③ Measurement Method When measuring current with the multimeter current range, connect the multimeter in series with the circuit under test. Only series connection ensures that the current flowing through the multimeter equals the current of the measured branch. Disconnect the measured branch and insert the red and black probes across the two broken points. Special attention: Never connect an ammeter in parallel with the circuit under test. This is hazardous and may burn out the multimeter instantly. Observe probe polarity: connect the red probe to the current‑inflow terminal and the black probe to the current‑outflow terminal of the circuit (the same polarity rule applies for DC‑voltage measurement).
④ Proper Scale Usage and Reading For DC‑current measurement, use the same top scale line as for voltage measurement (marked with "mA" on its right‑hand side). Scale characteristics and reading procedures are identical to those for voltage measurement.
For currents larger than 500 mA, use the 5 A range. Operation: set the selector switch to the 500 mA position, pull the red probe out of the original "+" jack, and insert it into the dedicated 5 A jack at the bottom‑right corner of the multimeter. Now large currents up to 5 A can be measured.
