Skills · skill
Using a Multimeter
Electronics · Beginner
- Difficulty
- Beginner
- Done When
- The reading agrees with what Ohm's law says it should be, and a fresh AA reads 1.55–1.6 V.
- Tools
- Digital multimeter with autorange, probes, alligator clips, a known-good battery to check it against.
- Category
- Electronics
- Summary
- Measuring voltage, current and resistance — the instrument that turns a circuit from a mystery into numbers.
Safety
Never measure resistance or continuity on a live circuit. Never put the meter across a supply while it is in current mode. Mains: one hand behind your back, probes with finger guards, and a CAT III meter.
Steps
Voltage: black lead in COM, red in V; select DC or AC; touch the probes across the component, black to ground.
Current: move the red lead to the A socket; break the circuit and put the meter in the gap; expect a fuse to blow if you forget to move it back.
Resistance: power off, part isolated; touch across it; open circuit reads OL.
Continuity: the beeper — a quick check for broken wires and blown fuses.
Diode test: forward reads about 0.6 V for silicon, OL reversed.
When a reading makes no sense, check the meter on something you know first.
The Science
Voltage is measured across two points, in parallel, by a meter of very high resistance so it draws almost nothing. Current is measured in series, through a meter of very low resistance, so it drops almost nothing — put it across a supply and you have made a short circuit through the meter. Resistance is measured by pushing a small known current and reading the voltage: Ohm's law with the meter supplying the current, so it only works on a dead circuit.
How It Fails
A blown internal fuse from measuring current across a battery. A reading of 0 V because you are in AC mode on a DC circuit. A resistance reading that changes as you touch it — your fingers are in parallel.
Referenced by
element
equation
machine
Open on the Skills shelf — the interactive card, the filters, and everything alongside it.