All sensor types have a measurement range and accuracy. Before use, the sensor accuracy is tested and documented to be within the defined accuracy specifications.
The change on accuracy over time due to minuscule damage, erosion, and other reasons is called drift. To make sure that drift doesn't cause inaccuracy in measurements, most loggers need to be recalibrated annually.
From a technical point of view, recalibration of temperature sensors is often unnecessary since drift is minimal. More often than not, temperature sensors remain stable for years. However, regulatory requirements set the pace for temperature sensor calibration as well.
Data loggers are often used in a GDP environment where food or pharmaceutical products are stored and transported. Regardless of the relevant GDP document you consult (FDA, EU, PDA, ISPE, WHO, USP or ICH), most require “calibrated sensors”. Certain interpretations also require an ISO 17025 calibration for cold chain processes.
Authorities may request calibration certifications for audits. For instance, you might be asked to provide the data and calibration certificates from the logger you used for a specific shipment last year. Logmore logger calibration certificates are available at any time on the logger's page in Logmore Cloud.
Calibration for quality control
Calibrations do not make a sensor more accurate, but rather act as a method of quality control. Several tests are run on the sensors both before and after they are installed into devices to make sure they operate as intended.
When a data logger leaves the factory it meets all requirements, which is often stated in a validation certificate, and it has a production calibration certificate.
Most regulations are not clear on the number of required calibration points and where to position them. Both EU GDP and WHO have set the following requirements:
- The data logger should be calibrated in 3 points. If fewer calibration points are chosen, a detailed technical rationale should be delivered including evidence that the sensor is stable over its operating range. For single-use, low-cost electronic indicators it is industry standard to only calibrate the sensors in one temperature point.
- The calibration points should cover the entire operating range of the specific application. For example would the calibration points -30°C, 0°C and +50°C cover all applications in frozen, refrigerated, and room temperature environment.