Resistance thermometers in digital sensors have low drift, so they do not usually require further adjustment. However, if sensor readings are outside tolerance, the equipment will likely have sustained damage and is due for replacement.
Similar procedures and terminology apply to the calibration of humidity sensors. In comparison to temperature sensors, humidity sensors have a higher risk of drift—in particular when they are used in extreme wet or extreme dry environments. Therefore, they are typically adjusted during re-calibration. The first calibration is called “as-found calibration” and documents the status before adjustment. The sensor is then adjusted by the measured deviation. Afterwards, the so-called “as-left calibration” is performed to check if the adjustment has been successful. If a temperature sensor is outside tolerance, it is likely that it has been polluted too much and/or is physically damaged. Therefore, it is typically exchanged.
What are the correct temperature points to calibrate cold chain data loggers?
Regulations do not specify the number of points and their values. Nonetheless, it is best to calibrate data loggers at three temperatures – unless there is a persuasive argument and clear evidence for fewer points.
Sensors must be stable within their specified operating conditions. Therefore, calibration points should cover the anticipated range. For instance, -30 °C, 0 °C and 50 °C would correctly monitor typical frozen, refrigerated, and room temperature environments.
Finally, it is acceptable to calibrate single-use and low-cost electronic indicators at only one temperature point.
