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Difficulty: MediumMultimeter: Voltage and Current Measurement

A maintenance electrician needs to verify the alternating-current (AC) voltage across the power terminals of an industrial exhaust fan using a manual-ranging digital multimeter. What is the correct sequential order of steps to safely and accurately complete this measurement?

  1. 1Insert the black test lead into the COM jack and the red test lead into the V/\Omega\text{V/\Omega} input jack.
  2. 2Rotate the selector switch to the highest available AC voltage (V∼\text{V}\sim) range setting.
  3. 3Touch the meter test probes in parallel across the two energized load terminals.
  4. 4Observe the display and step down the range selector only if a more precise reading is needed within allowable limits.

Answer

The proper procedural sequence begins with inserting the black lead into COM and the red lead into V/\Omega\text{V/\Omega}, rotating the dial to the highest AC voltage range, placing the probes in parallel across the energized terminals, and finally adjusting down the range selector if greater resolution is required.
Safely measuring line voltage requires establishing high internal meter impedance first by plugging into COM and V/\Omega\text{V/\Omega} jacks, pre-setting the dial to the highest AC voltage range to prevent overload, bridging the test leads in parallel across the live terminals, and subsequently stepping down to a lower range only if increased decimal precision is necessary.

Step-by-Step Solution

1
Configure the multimeter input jacks.
Black lead is secured in the COM jack and red lead is in the V/\Omega\text{V/\Omega} jack.
Ensures the meter is internally configured as a high-impedance voltmeter rather than a low-impedance ammeter, avoiding dangerous short circuits.
2
Select the measurement mode and highest scale.
Selector dial is positioned at the highest AC voltage setting (V∼\text{V}\sim).
Protects the internal meter circuitry against overload and overvoltage spikes when measuring unknown or high AC potentials.
3
Connect the probes to the circuit under test.
Probes contact the two energized fan supply terminals in parallel.
A voltmeter requires a parallel connection across the potential difference while the circuit remains closed and operating.
4
Evaluate the measurement and optimize resolution.
Voltage reading is recorded, or range is decreased if the value is safely below the next lowest threshold.
Optimizes decimal precision while guaranteeing the input voltage does not exceed the lower range maximum.

Key Concept

Safe procedural sequence for manual-ranging multimeter AC voltage measurement and parallel lead hookup.
Estimated Time:1m 0s
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Topics

Multimeter: Voltage and Current Measurement

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