Every operator eventually gets the same email: a screenshot of a recorder trace with a red circle around a peak, and the question “what happened here?”. The honest answer is that the peak alone tells you almost nothing. The shape around it tells you everything.
Three shapes worth knowing
The sawtooth
A sharp rise followed by a fast, clean recovery, repeated. That is door events. The plant is healthy — it pulls the temperature back every time — and the fix is operational: dock seals, dwell discipline, route sequencing. You will see this on almost every last-mile trace and it is usually acceptable.
The ramp
A slow, steady climb that never recovers. That is a plant or power problem: the machinery has stopped and you are watching passive hold expire in real time. The slope tells you the insulation quality. This one is urgent.
The step
An instant jump to a new value that then sits flat and stable. That is almost never product. That is a probe that has come loose from the load and is now reading return air, or a logger that has been moved. Investigate the sensor before you quarantine the pallet.
What the interval hides
A fifteen-minute logging interval can miss a six-minute excursion entirely. If a product is sensitive to short excursions, the interval is part of the specification, not an implementation detail. We log at five minutes on food lanes and two minutes on pharmaceutical lanes for exactly this reason.
The question to ask
Not “was there an excursion” but “was the product ever outside its band, for how long, and cumulatively how many times”. Stability data answers whether that matters. A single trace does not.
