Match each electrical measurement scenario with the correct digital multimeter (DMM) lead … — Armed Services Vocational Aptitude Battery (ASVAB)

Match each electrical measurement scenario with the correct digital multimeter (DMM) lead placement, selector dial setting, and circuit connection method.

Measuring the voltage drop across an illuminated $12\text{ V}$ automotive tail lampConnect red lead to $\text{V/}\Omega$ jack and black lead to $\text{COM}$ ; place probes in parallel across the load with dial set to $\text{DCV}$ .
Measuring $450\text{ mA}$ operational current flowing into a solid-state relayConnect red lead to $\text{mA/}\mu\text{A}$ jack and black lead to $\text{COM}$ ; insert meter in series with the circuit branch with dial set to $\text{DCA}$ .
Measuring $8.2\text{ A}$ total current supplied to an active cooling fanConnect red lead to high-current ( $10\text{ A}$ ) jack and black lead to $\text{COM}$ ; insert meter in series with the circuit with dial set to $\text{DCA}$ .
Measuring the line potential at a $120\text{ V}$ AC utility wall outletConnect red lead to $\text{V/}\Omega$ jack and black lead to $\text{COM}$ ; place probes in parallel across the receptacle terminals with dial set to $\text{ACV}$ .

Answer

Each measurement scenario correctly aligns with its unique combination of meter jack, dial mode, and circuit connection:

12\text{ V}

DC lamp voltage drop matches parallel connection using

\text{V/}\Omega

and

\text{COM}

\text{DCV}

;

450\text{ mA}

relay current matches series connection using

\text{mA/}\mu\text{A}

and

\text{COM}

\text{DCA}

;

8.2\text{ A}

fan current matches series connection using the

10\text{ A}

jack and

\text{COM}

\text{DCA}

;

120\text{ V}

AC outlet voltage matches parallel connection using

\text{V/}\Omega

and

\text{COM}

\text{ACV}

The correct pairings enforce all foundational meter rules: voltage is measured across a component in parallel using the volt/ohm jack in the appropriate DC or AC dial mode, while current is measured inline in series using the appropriate current jack (milliamp jack for fractions of an amp, and the 10A terminal for high currents) to protect internal fuses and ensure accurate readings.

Step-by-Step Solution

Differentiate between voltage and current measurement connection rules.

Voltmeters must always be connected in parallel across components without opening the circuit, whereas ammeters must always be connected in series by breaking the circuit line.

Voltmeters possess extremely high internal impedance to prevent loading the circuit, while ammeters possess near-zero internal impedance to allow current to pass through.

Distinguish between direct current (DC) and alternating current (AC) dial configurations.

Automotive DC systems and DC relay lines require the DCV and DCA functions, while standard utility electrical wall receptacles supply sinusoidal alternating voltage requiring the ACV function.

Selecting the incorrect waveform mode causes inaccurate readings, meter errors, or failure to register potential.

Determine the proper current input jack based on expected current magnitude.

Low current (

450\text{ mA}

) is safely routed through the standard fused milliamp/microamp (mA/

\mu

A) jack, whereas high current (

8.2\text{ A}

) must be routed through the dedicated

10\text{ A}

high-current terminal.

Placing currents above

200\text{--}500\text{ mA}

into the milliamp jack will instantly blow the internal meter fuse.

Key Concept

Digital Multimeter Voltage and Current Configuration

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