A multimeter measures voltage by connecting in parallel, current by connecting in series, and resistance across an unpowered component. Select the correct mode, sockets, and range before attaching the probes.
Measurement Procedure
Insert the black lead into COM. For voltage and resistance, place the red lead in the socket; for current, use the appropriate fused or socket.
| Quantity | Connection and setting | Procedure |
|---|---|---|
| Voltage | Select AC or DC voltage; connect in parallel | Keep the circuit powered. Place one probe on each side of the component. For DC, red normally connects toward higher potential and black toward lower potential. |
| Current | Select AC or DC current; connect in series | Break the circuit and insert the meter so all measured current passes through it. Begin with the highest suitable range. |
| Resistance | Select resistance; connect across the component | Switch off and disconnect the supply. Ideally isolate one terminal to prevent alternative circuit paths affecting the reading. |
With a manual-ranging meter, start above the expected value. An overload indication requires a higher range; poor resolution suggests a lower range. An auto-ranging meter chooses the numerical range automatically, but you must still select the correct measurement mode.
The main safety risk occurs during current measurement. Never connect a meter set to current directly across a power supply: this creates a low-resistance path, which can blow the fuse or damage the meter and circuit. Disconnect power before changing sockets.
A common misconception is that every multimeter measurement is made across a component. Only voltage and resistance use parallel connections; measuring current requires the meter to become part of the circuit.
IB Exam Technique
For B3.4 Electronic systems application and selection (HL only), state the mode, sockets, connection, power condition, and safety precaution. Show the voltmeter in parallel and ammeter in series.
