Sensor Calibration, Verification and Drift: Three Different Questions

A sensor that displays a stable number is not necessarily accurate. Measurement systems can show bias, changes over time, poor placement or unsuitable response characteristics. Three terms help separate the issues: calibration, verification and adjustment.

Calibration is a documented comparison

Calibration establishes a relationship between instrument indications and reference values under stated conditions. It does not automatically mean the device was adjusted, and it does not establish permanent accuracy. The uncertainty and traceability of the reference measurements matter.

Verification answers a narrower question

Verification asks whether an instrument meets defined requirements at the time of the check. A simple cross-check against another unverified sensor may reveal a disagreement, but it cannot prove which instrument is correct. Adjustment changes instrument behavior; it should be recorded separately from the original calibration result.

What about drift?

Drift is a change in indication over time under comparable conditions. Detecting it requires a meaningful baseline and repeat checks, not just observing fluctuations while the environment itself changes. Record sensor ID, calibration date, reference source, environmental conditions, observed error, corrective action and the next review date.

Make comparisons fit the application

A temperature probe, humidity sensor and electrical-conductivity meter measure different quantities and require different verification methods. Follow manufacturer-specific procedures and avoid transferring a tolerance from one instrument class to another. The Journal's Data Logger Guide explains why placement and recording practices matter.

References and further reading

NIST: Metrological Traceability—Frequently Asked Questions and Policy; NIST: Traceability Considerations for Measuring Systems.

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