Examkin

Question

Difficulty: MediumMultimeter: Voltage and Current Measurement

An electronics technician needs to measure the direct current (DC) drawn by an indicator circuit operating on a 28 V28\text{ V} DC bus using a digital multimeter (DMM). Place the following procedural steps in the correct chronological order to perform this measurement safely and accurately.

  1. 1De-energize the circuit by opening its power switch or circuit breaker to prevent arcing and accidental short circuits.
  2. 2Insert the red test lead into the high-current (10 A10\text{ A}) jack, insert the black lead into the COM\text{COM} jack, and set the rotary selector to DC current (ADC\text{A}_{\text{DC}}).
  3. 3Physically open the current path by disconnecting one conductor or terminal at the desired measurement point.
  4. 4Connect the multimeter test probes in series across the open break so that all circuit current must flow through the meter.
  5. 5Re-energize the circuit and observe the stable current measurement on the digital display.

Answer

The correct sequence begins with de-energizing the circuit, configuring the multimeter jacks and selector dial for DC current, opening a physical break in the circuit path, connecting the meter leads in series across the opening, and finally re-energizing the circuit to read the display.
Measuring electrical current requires the meter to become part of the conductive path (in series). Therefore, the correct procedure must start with safely de-energizing the circuit, configuring the multimeter's leads to the high-current (10 A10\text{ A}) and common jacks with the dial set to DC current, opening a physical break in the circuit, connecting the probes across that break to complete the path in series, and lastly re-energizing the circuit to read the measured amperage.

Step-by-Step Solution

1
De-energize the circuit power source.
Voltage and current flow are reduced to zero across all circuit components.
Safety protocol dictates that power must be disconnected before opening conductors to avoid electrical shock, short circuits, or component damage.
2
Configure the multimeter leads and selector switch.
The red lead is inserted into the fused 10 A10\text{ A} port, black in COM\text{COM}, and the dial is rotated to DC amperes (ADC\text{A}_{\text{DC}}).
Setting the meter to the highest current range prior to measurement protects the internal current-sensing shunt and fuse from inrush current.
3
Open the conductor at the point of measurement.
A physical gap is created in the single conductive loop.
Current represents the rate of charge flow through a loop; the loop must be opened so the ammeter can become an integral link in that loop.
4
Attach the meter test probes in series across the gap.
The low-resistance internal ammeter circuit bridges the gap and completes the circuit path.
Connecting an ammeter in parallel across an active voltage source causes a catastrophic short circuit, whereas a series connection allows proper inline current sensing.
5
Reapply power and record the reading.
Current flows through the load and the meter, displaying the direct current value in amperes or milliamperes.
Current can only flow and be quantified when the circuit is actively powered.

Key Concept

Series Ammeter Insertion and Meter Configuration Protocol
Estimated Time:1m 0s
Rate this question

Topics

Multimeter: Voltage and Current Measurement

More questions from this topic