Blog · 2026-08-18
Why a 30-second reset became 30 minutes
Four ways to express integral time, two of them running in opposite directions, and the single conversion that catches the mistake before it reaches a live loop.
The number that looked right
A flow loop was sluggish, so the integral time was shortened to thirty seconds. The change was entered into a controller that expressed reset differently, and the value landed as eighteen hundred seconds — thirty minutes. The loop got slower, not faster, and it took weeks to notice because the number on the screen looked perfectly reasonable.
Four ways to say the same thing
Integral time is the same quantity in every controller, but it is written down four different ways: minutes per repeat, seconds per repeat, repeats per minute, and repeats per second. The first two are a time per repeat and differ by a factor of sixty. The last two are repeats per time, and they are the reciprocals of the first two — a larger number means faster reset rather than slower.
The same thirty-second integral time is 0.5 minutes per repeat, or 30 seconds per repeat, or 2 repeats per minute. Carry the number for one convention into a field that expects another, and the loop is tuned to a value that is wrong by a factor of sixty, or backwards altogether.
Why the error survives review
Each number is plausible on its own. Thirty seconds and thirty minutes are both ordinary integral times; 0.5 and 2 are both ordinary-looking reset values. Nothing flags the mistake until someone redoes the conversion by hand — and the whole reason the value was being changed was that the loop was misbehaving, so a loop that is still misbehaving afterwards is easy to write off as the loop.
The check that catches it
Convert the value to a common unit — seconds per repeat — and ask whether the result is physically sensible for the loop. A flow loop with an integral time of thirty minutes is an integrating response with the brakes on; a temperature loop with an integral time of two seconds is a loop chasing its own noise. If the converted number looks wrong, it is wrong.
The reset-units converter does exactly this conversion in both directions, so the arithmetic you would otherwise do in your head, standing in front of a live console, is done once and checked.