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Difficulty: MediumMultimeter: Voltage and Current Measurement

A technician is preparing to measure the direct current flowing through an active 12 V12\text{ V} DC relay coil with an expected load current of approximately 150 mA150\text{ mA}. Which multimeter setup and circuit connection method is correct?

  1. A
    Insert the black lead into COM, the red lead into the mA terminal, set the selector dial to DC milliamperes, and connect the meter in parallel across the relay coil.
  2. Insert the black lead into COM, the red lead into the mA terminal, set the selector dial to DC milliamperes, and insert the meter in series by opening the circuit line.Answer
  3. C
    Insert the black lead into COM, the red lead into the V/\Omega terminal, set the selector dial to DC volts, and connect the meter in series by opening the circuit line.
  4. D
    Insert the black lead into COM, the red lead into the mA terminal, set the selector dial to AC milliamperes, and insert the meter in series by opening the circuit line.

Answer

Insert the black lead into COM, the red lead into the mA terminal, set the selector dial to DC milliamperes, and insert the meter in series by opening the circuit line.
To measure current accurately and safely, the multimeter must be placed in series with the load by opening the circuit path so that the circuit current passes through the meter. Additionally, the black lead must connect to the common port (COM), the red lead must connect to the appropriate current input port (mA for 150 mA150\text{ mA}), and the selector dial must be set to DC milliamperes.

Step-by-Step Solution

1
Determine input terminal and selector dial requirements based on the measurement type and quantity.
The target is direct current at 150 mA150\text{ mA}, requiring the red probe in the mA\text{mA} jack, black probe in COM\text{COM}, and dial set to DC mA\text{DC mA}.
Multimeters use dedicated low-resistance fused input jacks for current measurements and separate modes for alternating versus direct current.
2
Determine the required electrical connection configuration within the circuit.
The circuit must be opened so that the ammeter is inserted in series with the relay load.
Current represents the flow of charge through a pathway; all electrons must physically pass through the ammeter to be counted.

Key Concept

Digital Multimeter Current Measurement Hookup and Jack Configuration
Estimated Time:1m 0s
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Topics

Multimeter: Voltage and Current Measurement

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