問58
頻出度★★★
装置のライフサイクルを故障の面から見てみると, 時間経過によって初期故障期, 偶発故障期及び摩耗故障期に分けられる。最初の初期故障期では, 故障率は時間の経過とともに低下する。やがて安定した状態になり, 次の偶発故障期では, 故障率は時間の経過に関係なくほぼ一定になる。最後の摩耗故障期では, 故障率は時間の経過とともに増加し, 最終的に寿命が尽きる。このような故障率と時間経過の関係を表したものを何というか。
平成30年度 秋期 ITパスポート試験 問58
テクノロジ系システム構成要素 › システムの評価指標
This question's explanation and your answers so far.
解説
問 58
Incorrectア
A Gantt chart is a diagram that arranges tasks (jobs) as horizontal bars in chronological order to manage the progress of processes and schedules; it does not express the relationship between failure rate and time.
Incorrectイ
A reliability growth curve is a software-development curve that shows the cumulative number of bugs detected and removed (the degree of improvement in reliability) as testing and debugging progress; it does not express how a device’s failure rate changes over time.
- ウ
正解 The correct answer is “ウ Bathtub curve.” Looking at a device’s failure rate over time: in the early-failure period the failure rate falls from a high level, in the random-failure period it stabilizes at a roughly constant low value, and in the wear-out-failure period it rises again. Because this shape of “falling, then flat, then rising” resembles the cross-section of a bathtub, the curve that expresses the relationship between the failure rate and the passage of time is called the bathtub curve. The description of the three periods in the question is exactly the definition of the bathtub curve itself.
Incorrectエ
A radar chart is a diagram that places multiple evaluation items on radial axes and represents their balance as a polygon; it does not express the change in failure rate along the passage of time.
ここがポイント
- Bathtub curve: it represents the change of the failure rate over time in three periods — early-failure period (decreasing), random-failure period (roughly constant), and wear-out-failure period (increasing) — and its name comes from its shape resembling the cross-section of a bathtub.
- Telling the confusingly similar diagrams apart: a Gantt chart (process and schedule management), a reliability growth curve (cumulative number of bugs), and a radar chart (balance across multiple items) each serve a different purpose.
用語