How temperature data loggers are calibrated

A data logger's reading is the output of its sensor, its analogue electronics and its firmware. Calibrating the sensor alone would miss the rest, so loggers are normally calibrated as a whole, reading their logged values against a reference thermometer placed alongside them.

Typical approach

• Environmental chamber (or bath for probe-type loggers) held at each calibration point until stable.
• Reference thermometer close to the loggers, at the same height and airflow.
• Calibration points spanning the use range — for 2–8 °C use, typically around 2, 5 and 8 °C or wider.
• Sufficient dwell time for the logger's response, then several logged readings compared with the reference.
• Corrections and uncertainty reported per point.

Watch for

Chamber uniformity and stability dominate the uncertainty; the logger's own resolution (often 0.1 °C) and response time matter; and the calibration must be at the points the logger will be used at — a calibration at 25 °C says little about 4 °C.