Follow Testo model methods, calibrate annually, maintain ISO and NATA traceability, and keep records auditors can verify during an inspection.
Calibrate Testo data loggers at least annually, and more often where the risk assessment demands it. Every calibration event needs a traceable reference standard, recorded as-found and as-left readings, and strict adherence to the model-specific Testo procedure. Skip any of these three, and the certificate you hold will not stand up to an audit.
TL;DR:
- Shorten intervals for cold chain assets, harsh conditions, or a history of drift, and prioritize pharmaceutical monitors over stable ambient units.
- Follow each model’s manual: temperature loggers may require full immersion, while humidity units need a chamber; allow 30 to 60 minutes for temperature points to settle.
- Audit ready certificates should report expanded uncertainty at k=2 for each point, identify the logger by serial number, and include reviewer approval.
- When a reading before adjustment falls outside tolerance, review data batches collected since the last successful calibration, and retain certificates for the asset’s full life.
- Calibration confirms sensor accuracy, while validation checks performance in the installed location, including response time and placement; schedule these as separate activities.
The right interval depends on four things: what the manufacturer recommends, how critical the measurement is, how the logger has drifted historically, and the conditions it works in. A logger monitoring a walk-in freezer in a pharmaceutical warehouse carries more risk than one tracking ambient temperature in a dry store, even if both are the same model.
Annual recalibration is the standard baseline for most Testo loggers used in commercial settings, and Testo’s own product manuals typically reflect this recommendation for models such as the testo 190 series. Shorten that interval when the asset supports cold chain logistics, has a history of drifting out of tolerance, or operates in harsh conditions such as high humidity, vibration or frequent temperature cycling.
Calibration method depends on the logger design:
Calibration should typically cover multiple points across the logger’s working range, using at least two or three set points, rather than a single midpoint check; for detailed methods on precision approaches in industrial measurement, see precision engineering for oil & gas. Stabilisation matters just as much as the reference itself: temperature set points generally need 30 to 60 minutes to settle, while humidity equilibration takes longer and depends on good air circulation inside the chamber.
Pro Tip: Run a pre-check on battery level and display readout before you start, so a flat battery or sensor fault does not get mistaken for drift.
Testo’s own instruction manuals set out calibration methods that differ by model, and following them exactly is what keeps a certificate defensible. The testo 190 data logger instruction manual specifies full immersion in a liquid bath for many temperature variants, along with model-specific recalibration intervals that commonly sit at 12 months.
Key points to check against the manual for your specific model:
A certificate issued without following the manufacturer’s stated method is weaker evidence in an audit, because the assessor has no way to confirm the readings reflect how the logger actually performs in service. When in doubt, the manual takes precedence over a generic calibration script.
Traceability is the backbone of a defensible calibration, and it means every reference standard used in the process can be linked, through an unbroken chain of comparisons, back to a national or international measurement standard. ISO/IEC 17025 sets the competence requirements that testing and calibration laboratories must meet to issue results that carry this kind of weight, and NATA’s traceability guidance explains the accepted paths for establishing it, including what to do when an accredited lab is not available.
A single detail separates a usable certificate from a decorative one: whether it reports expanded uncertainty at a coverage factor of k=2, as required under ISO/IEC 17025. Without that figure, you cannot judge whether the reference standard was accurate enough for your tolerance requirements, a comparison known as the test uncertainty ratio.
A complete, audit-ready certificate should include:
When an accredited laboratory genuinely is not available for a given measurement, NATA guidance expects extra supporting evidence: method validation records, equipment logs and an independent cross-check against a higher-accuracy reference. That evidence has to be ready to produce at assessment, not assembled afterwards. Quality teams specifying new equipment can also check our guidance on requesting NATA traceable data loggers before a purchase goes ahead.
The certificate is only half the job. What happens to that data afterwards determines whether it protects you in an audit or sits unused in a folder. The CASRAI guidance on data logger calibration treats as-found and as-left readings as the core evidence for any retrospective impact assessment, because as-found tells you how the logger was actually performing before anyone touched it.
Minimum fields every record needs:
Retain certificates for the life of the asset at minimum, and link them directly to the equipment record so anyone auditing a batch of historical data can pull the relevant calibration instantly. Our article on verifying traceable versus accredited calibration walks through the specific documents quality teams should ask for.
Pro Tip: When an as-found reading falls outside tolerance, do not just recalibrate and move on. Review every batch of data collected since the last successful calibration to assess what the drift means for product or process records.
Calibration confirms the sensor’s accuracy; validation (or qualification) confirms the logger performs correctly once placed in its working location, accounting for response time and positioning. The two are not interchangeable, and a compliance programme that only calibrates without validating has left a gap.
A documented, risk-based interval policy only works if it gets reviewed every time an as-found reading fails. Treat each failure as a signal to shorten the interval for that asset, not just a one-off fix.
Between calibrations, a short routine inspection catches problems early:
Store loggers in a stable environment away from extreme temperature swings, and avoid dropping or knocking probe-through-body models during transport, since mechanical shock is a common cause of sensor drift. An unexplained reading, a failed as-found check, or a logger returning from a harsh deployment are all signals that justify an interim recalibration ahead of schedule.
Calibration only produces reliable evidence when the right people do the right parts of the job. Four roles cover it: the asset owner who sets the interval policy, the coordinator who schedules and tracks it, the technician who performs the test, and the reviewer who checks and signs the certificate before it is filed.
A technician’s evidence should always show the method steps followed, the stabilisation time observed, and a check that the reference standard’s own certificate is current and traceable.
The most common pitfalls, in order of how often they undermine a certificate:
A simple SOP checklist, covering pre-check, method, stabilisation time, reference verification and sign-off, closes most of these gaps before they happen.
We provide calibration for Testo data loggers alongside multi-brand servicing, so your fleet does not need separate providers for different equipment brands. Every certificate we issue carries traceability, as-found and as-left readings, and uncertainty reporting in line with the practices covered above.
Most teams calibrate whatever is due next, not whatever matters most. A better approach triages by criticality, drift history and regulatory exposure: cold chain and pharmaceutical-grade loggers go first, stable ambient monitors can wait. Build a simple matrix, three risk tiers against calibration due dates, and you will find budget for the assets that would actually hurt you in an audit. Schedule a full validation exercise separately, once calibration coverage across the fleet is solid.
— Kaz
We offer NATA-accredited calibration and traceable calibration for Testo data loggers, built around the same practices covered in this guide: full traceability, as-found and as-left readings, and uncertainty reporting on every certificate. You do not need to chase separate providers for different brands in your fleet, we cover Testo alongside the other measurement equipment you rely on.
Request a quote through our calibration services page and we will confirm lead time and documentation requirements for your specific Testo models.
The procedure checks the logger’s readings against a traceable reference standard at multiple points across its working range, after allowing stabilisation time. Results are recorded as as-found (before adjustment) and as-left (after adjustment), with the reference’s uncertainty stated on the certificate.
Follow the model-specific method in Testo’s own instruction manual, which for many temperature models means full immersion in a liquid bath against a traceable reference. Check the testo 190 manual for your exact model’s immersion depth and stabilisation requirements, and record both as-found and as-left readings.
A data logger automatically records environmental measurements, such as temperature or humidity, over time without constant manual checking. It supports compliance monitoring in sectors like food, pharmaceuticals and manufacturing, where continuous evidence of conditions is required.
A good logger matches your working range, required accuracy and environment, with models such as the testo 175 H1 suited to combined temperature and humidity monitoring. Check that the supplier can also provide NATA-accredited calibration with traceable certificates, since the logger is only as good as its calibration record.
