期間が経過すると

Which is better, "when a first predetermined period has elapsed" or "after a first predetermined period has elapsed"?

ChatGPT:

Both "when a first predetermined period has elapsed" and "after a first predetermined period has elapsed" are grammatically correct and natural, but there is a slight nuance between them:

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🔹 "when a first predetermined period has elapsed"

• Emphasizes the exact timing — the event (e.g., stopping voltage) happens at the moment the period ends.

• Often used in control logic, programming, or technical contexts where precision matters.

✅ Preferred when the action should occur immediately at the completion of the period.

“The control device stops voltage application when a first predetermined period has elapsed.”
⟶ Implies the stopping happens right at the end of that period.

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🔹 "after a first predetermined period has elapsed"

• Slightly more relaxed — implies the event happens sometime following the end of the period, not necessarily at the exact moment.

✅ Appropriate when the timing is less precise, or to emphasize sequence rather than simultaneity.

“The control device stops voltage application after a first predetermined period has elapsed.”
⟶ Could mean a short delay after the period ends.

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✅ Recommendation for technical or patent writing:

“when a first predetermined period has elapsed”
is slightly better if you're trying to convey precise control behavior (which is typical in such documents).