Qualifying a temperature monitoring system
Installation checks, functional tests covering alarm and failure modes, and a performance period in routine use, plus the software validation underneath.
A monitoring system is both a measuring system and a computerised system, so its qualification draws on both ISO/IEC 17025-style metrological evidence and Annex 11-style software controls.
OQ tests that are often missed
- Sensor removed or failed: does the system alarm, and does the record show the gap?
- Gateway or network down for an hour: are data back-filled, in order, without duplicates?
- Clock changes and time zones: are timestamps consistent?
- User without rights attempts to change an alarm limit: is it refused and logged?
- Alarm acknowledged but condition persists: does it re-alarm or escalate?
The PQ period ends with a report confirming the system is fit for use and defining the routine review, calibration and periodic-review arrangements.
The OQ tests that find real problems
Installation checks and a set-point comparison will pass on almost any system. The tests that discriminate are the failure-mode tests, because they exercise the behaviour the system exists for and the behaviour nobody has ever seen.
| Test | What to do | Typical finding |
|---|---|---|
| Sensor removed or disconnected | Unplug a probe and wait | The system logs nothing and raises nothing — silence indistinguishable from normal |
| Network or gateway down | Disconnect for an hour, then restore | Data not backfilled, or backfilled out of order, or duplicated |
| Mains power lost | Pull power for the rated backup period | Backup battery long dead; no alarm on the loss itself |
| Clock change | Cross a daylight-saving boundary, or change the time zone | Duplicated or missing hour, silently reordered |
| Alarm escalation | Trigger a real alarm at 02:00 and do not acknowledge it | Second and third contacts never called; the chain existed only in the configuration |
| Alarm threshold and delay | Warm a probe through the limit at a controlled rate | Delay far longer than configured, or threshold applied to a smoothed value |
Challenge the alarm properly
An alarm test that consists of changing the threshold to below the current temperature proves the software can compare two numbers. The test that matters warms a real probe through the real limit at a realistic rate and measures three things: when the reading crossed, when the notification arrived, and whether the event appears in the audit trail with a consistent timestamp. Record all three with times, not a tick.
The two halves of the qualification
- Metrological: sensors calibrated at the points they will police, with certificates covering the range; placement justified by the mapping study; uncertainty known and reflected in the alarm limits.
- Computerised system: Annex 11 applies. Individual user accounts rather than a shared login, an audit trail that cannot be disabled, time synchronisation to one source, a supplier assessment on file, and a backup that has been restored at least once to prove it works.
- The PQ is a period of routine use, reviewed at the end for gaps, nuisance alarms, unacknowledged events and sensors that quietly stopped reporting.
- The PQ report defines what happens afterwards: review frequency, calibration intervals, and when the system is requalified.
A shared login makes an audit trail worthless, because every entry names the same account. It is the single most common Annex 11 finding on monitoring systems, and it is free to fix.
Frequently asked questions
- How long should PQ run?
- Long enough to see routine operation including door traffic, defrost cycles and at least one alarm event — commonly two to four weeks for storage systems.
References
- [1]WHO Technical Supplement 16 to TRS 961 Annex 9: Environmental temperature monitoring systems for fixed storage areas
- [2]EudraLex Volume 4, Annex 11: Computerised Systems
- [3]ISO/IEC 17025:2017 — General requirements for the competence of testing and calibration laboratories
General technical guidance written against the cited sources. It is not regulatory or legal advice and does not replace the applicable standard, guideline or a qualified reviewer's judgement.
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