An electronics technician is setting up a digital multimeter (DMM) to perform several diag… — Armed Services Vocational Aptitude Battery (ASVAB)

An electronics technician is setting up a digital multimeter (DMM) to perform several diagnostic checks on a circuit test bench. Match each measurement task to its correct meter input jack, dial setting, and circuit connection method.

Measuring a low $18\text{ mA}$ direct current flowing through a transistor bias networkRed lead in $\text{mA}/\mu\text{A}$ jack, black in $\text{COM}$ , dial on $\text{DC mA}$ , connected in series with the opened circuit
Checking for standard $120\text{ V}_{\text{RMS}}$ AC line voltage at a power receptacleRed lead in $\text{V}/\Omega$ jack, black in $\text{COM}$ , dial on $\text{ACV}~(\sim\text{V})$ , connected in parallel across the terminals
Measuring a heavy $7.5\text{ A}$ direct current drawn by a DC motor drive circuitRed lead in $10\text{A}$ high-current jack, black in $\text{COM}$ , dial on $10\text{A DC}$ , connected in series with the opened circuit
Verifying a steady $24\text{ V}$ DC potential difference across a filtering load resistorRed lead in $\text{V}/\Omega$ jack, black in $\text{COM}$ , dial on $\text{DCV}~(=\text{V})$ , connected in parallel across the component

Answer

Match small DC current (

18\text{ mA}

) with the

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

jack in series; match

120\text{ V}

AC line voltage with the

\text{V}/\Omega

jack on

\text{ACV}

in parallel; match heavy DC current (

7.5\text{ A}

) with the dedicated

10\text{A}

jack in series; match

24\text{ V}

DC potential difference with the

\text{V}/\Omega

jack on

\text{DCV}

in parallel.

Correct multimeter configuration requires matching three parameters: (1) connection topology (parallel for voltage, series for current), (2) input terminal selection (standard

\text{V}/\Omega

for voltage, low-current

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

for values under

400\text{ mA}

, and separate

10\text{A}

terminal for high current), and (3) function selection matching waveform type (DC vs. AC).

Step-by-Step Solution

Determine connection topology based on measurement quantity (Voltage vs. Current)

Voltmeters must always be connected in parallel across components, while ammeters must always be placed in series by breaking the circuit path.

Voltmeters have high internal input impedance (

>10\text{ M}\Omega

) to prevent loading, whereas ammeters have near-zero internal resistance to allow current flow.

Select input jacks based on expected signal magnitude and function

Voltage readings use the

\text{V}/\Omega

and

\text{COM}

jacks. Current below

400\text{ mA}

uses the

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

jack, while high current (

7.5\text{ A}

) requires the separate

10\text{A}

high-current terminal.

Exceeding the current rating of the low-current jack will immediately blow the internal protective fuse.

Select dial settings based on waveform type (AC vs. DC)

Use

\text{ACV}

for

120\text{ V}_{\text{RMS}}

utility power,

\text{DCV}

for

24\text{ V}

filtered direct potential,

\text{DC mA}

for

18\text{ mA}

, and

10\text{A DC}

for

7.5\text{ A}

Setting an AC mode on a DC signal or vice versa leads to erroneous readings or reading zero due to average vs. RMS rectification filtering.

Key Concept

Multimeter Lead Placement, Jack Selection, and Dial Configuration

Estimated Time:2m 0s

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

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