Temperature Calibration: All You Need to Know About Temperature Sensor Calibration

Why a Temperature Calibration is Necessary
From a Regulatory Perspective

Why a Temperature Calibration is Necessary
From a Technical Perspective

The core of each Data Logger is its measurement sensor. Each sensor type has a specific measurement range and accuracy and different strengths and weaknesses. Before the sensors are installed into a data logger, each sensing element is calibrated, i.e. tested on its accuracy, documented and thus exactly within the defined specification. The change of the accuracy over time is called “drift”. After one year, the sensor will be recalibrated to verify if the sensor accuracy is still within specification.

To understand the term calibration, it is vital to know about the physical and technological properties of a data logger and its life-cycle. Calibration as such is not making a sensor more accurate. Accuracy is a quality built by design. The right sensor is chosen already during the engineering of a data logger and carefully built into the device using the right algorithm. Each sensor is calibrated already during production before it is build into the data logger. Afterwards, several checks and sample tests are performed in order to verify that the product meets all requirements – including accuracy. So 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.

Why to Re-Calibrate Temperature and
Humidity Sensors After One Year?

From a technical point of view, recalibration of temperature sensors makes little sense, as the risk of drift is minimal and there are indications that these sensors will be stable for many years. So why replace or calibrate temperature sensors after one year? Due to regulatory requirements. Regardless which guidance document in the GxP-environment one consults (FDA, EU, PDA, ISPE, WHO, USP or ICH) – in general they all require “calibrated sensors”. While some guidance documents are more general and just write “calibrated sensors must be used”, others are more specific requesting “regularly calibrated sensors” or even “yearly calibrated sensors”. Some auditors even tend to do an extreme interpretation of the regulations requiring "ISO 17025 calibrated single-use sensors" for transportation. There is no general rule of what regulation requires but most auditors appreciate a risk based approach considering the measurement range of the application as well as the type of sensor used.

What is ISO 17025?

ISO 17025 is the international standard for calibrations. The general requirement to issue ISO 17025 certificates are:

• The company (and in particular the laboratory) must have an ISO 9001 certified quality management system, which means that all processes must be documented.
• The laboratory as such must be mapped and accredited by local authorities (e.g., Switzerland: SAS/SCS, USA: ANAB, Germany: DaaKs, UK: UKAS)
• The calibration method used, including measurement uncertainties, must be documented and accredited by the local authorities.

What is the difference between a factory calibration and an ISO 17025 calibration?

Technically, the two calibrations are identical, except two additional criteria for ISO 17025:

1. Not 2-eye but 4-eye approval
2. The entire process is not just GAMP®5 validated but also approved by the accreditation body.

Although the main difference is the price (the exact same processes and devices are used, the same tolerances applied, and the certificate almost looks the same) - why is the ISO 17025 certificate to popular with auditors? Usually auditory have few specialty knowledge on calibrations. ISO 17025 is a known standard: "I can rely on this certificate, since the process has been approved by an official regulatory body".

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