A technician needs to measure the direct current flowing through a 12\text{ V} automotive … — Armed Services Vocational Aptitude Battery (ASVAB)

A technician needs to measure the direct current flowing through a $12\text{ V}$ automotive cooling fan circuit that is expected to draw approximately $3.2\text{ A}$ . Which multimeter configuration and connection method must be used to obtain an accurate reading without damaging the meter or blowing its internal fuse?

A
Insert the red probe into the $\text{V}/\Omega/\text{mA}$ jack, black probe into $\text{COM}$ , select the $\text{DC mA}$ dial setting, and connect the meter in series with the motor.
Insert the red probe into the $10\text{ A}$ jack, black probe into $\text{COM}$ , select the $\text{DC A}$ dial setting, and connect the meter in series with the motor.Answer
C
Insert the red probe into the $10\text{ A}$ jack, black probe into $\text{COM}$ , select the $\text{DC A}$ dial setting, and connect the test probes in parallel across the motor terminals.
D
Insert the red probe into the $10\text{ A}$ jack, black probe into $\text{COM}$ , select the $\text{AC A}$ dial setting, and connect the meter in series with the motor.

Answer

Insert the red probe into the

10\text{ A}

jack, black probe into

\text{COM}

, select the

\text{DC A}

dial setting, and connect the meter in series with the motor.

Measuring current requires placing the multimeter in series with the load so all electron flow passes through the instrument. Because the expected current is

3.2\text{ A}

, the positive lead must be plugged into the high-current

10\text{ A}

input jack to prevent blowing the lower-rated milliamp fuse. Furthermore, because the source is automotive

12\text{ V DC}

, the function dial must be configured to direct current (

\text{DC A}

Step-by-Step Solution

Select the appropriate current range and input jack based on anticipated current magnitude.

The red lead must be placed in the dedicated

10\text{ A}

high-current jack rather than the

\text{V}/\Omega/\text{mA}

jack.

The circuit draws approximately

3.2\text{ A}

(

3200\text{ mA}

), which far exceeds the standard

200\text{ mA}

500\text{ mA}

limit of the fused low-current jack.

Set the multimeter function selector switch to the correct electrical mode.

The selector switch must be rotated to the direct current amperes (

\text{DC A}

A\overline{--}

) position.

An automotive fan operates on a direct current (

12\text{ V DC}

) source, requiring the meter to measure unidirectional current flow rather than alternating current.

Connect the multimeter probes properly into the physical circuit.

Break the circuit path and place the meter leads in series with the load.

Current represents the rate of charge flow through a conductor; therefore, all current must flow through the meter's low internal shunt resistor in series to be measured.

Key Concept

Multimeter Current Measurement and Input Jack Protection

Estimated Time:1m 15s

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Topics

More questions from this topic