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Difficulty: MediumMultimeter: Resistance and Continuity

A technician is using a digital multimeter set to the resistance (ΩΩ) function to test a de-energized DC solenoid valve coil with a nominal rating of 24 Ω24\ \Omega. Which multimeter display reading indicates that the solenoid coil has an internal open circuit?

  1. A
    0.0 Ω0.0\ \Omega
  2. B
    24 Ω24\ \Omega
  3. OL\text{OL} (over-limit) or infinite resistanceAnswer
  4. D
    24 kΩ24\ \text{k}\Omega

Answer

An over-limit (OL) or infinite resistance reading on the digital multimeter display indicates an open circuit.
An open circuit occurs when there is a physical break in the conductive path of the coil winding. Because electric current cannot bridge the gap, the electrical resistance across the terminals becomes infinite (∞\infty). On a digital multimeter, infinite resistance that exceeds the instrument's measurement capability is displayed as 'OL' (over-limit).

Step-by-Step Solution

1
Identify the electrical state being tested on the de-energized coil.
An internal open circuit means the continuous wire winding has broken, creating an incomplete path.
When a conductor or winding breaks, current can no longer pass through the component.
2
Determine the theoretical resistance value of an open circuit.
An open circuit provides infinite resistance (∞ Ω\infty\ \Omega) to the multimeter's internal test current.
Air or physical gaps between broken wire ends have extremely high dielectric resistance.
3
Correlate infinite resistance with standard digital multimeter display conventions.
Digital multimeters display infinite resistance exceeding the measurement range as 'OL' (over-limit) or '∞\infty'.
Multimeters use 'OL' to indicate that the measured resistance exceeds the measurable range of the selected scale.

Key Concept

Interpreting digital multimeter resistance displays for open circuits versus normal continuity
Estimated Time:1m 0s
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Topics

Multimeter: Resistance and Continuity

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