Temperature sensor calibration:
frequency, traceability and documentation.

Periodic calibration is a requirement in regulated environments. But the right frequency is not universal, it depends on the application, the instrument's history and the standard adopted as a reference.

What calibration is

Calibration is the process of comparing the value indicated by an instrument with a traceable reference standard. Metrological traceability is organized internationally through accredited calibration laboratories under ISO/IEC 17025 and the ILAC-MRA mutual recognition arrangement.

The result of calibration is a certificate documenting the instrument's error on the date of the test, and the uncertainty associated with that measurement. It does not guarantee that the sensor is more accurate after the process; it provides documented evidence of how the instrument behaved.

Who defines the frequency

There is no single legally defined frequency for all sensors in all contexts. The calibration interval results from the combination of:

• The requirement of the operation's reference standard (e.g. ISO/IEC 17025 for accredited laboratories, GDP/GxP frameworks for pharmaceuticals)
• The equipment manufacturer's recommendation
• The instrument's behaviour history in previous calibrations
• The criticality of the application and the consequences of an incorrect reading

Factors that shorten the interval

Some contexts justify shorter intervals:

• Harsh environment, extreme temperature, high humidity, constant vibration
• A history of deviations detected in previous calibrations
• A high-risk product or process in the event of an incorrect reading
• An explicit requirement from the client or the regulatory body

In stable environments, with a consistent history and no specific standard requirement, longer intervals may be justified, as long as they are documented and reviewed periodically.

What the calibration certificate must contain

A certificate issued by an accredited calibration laboratory should include:

• Instrument identification (manufacturer, model, serial number)
• Calibration date and the responsible laboratory
• Standards used and their traceability
• Results, indicated values vs. reference values
• Measurement uncertainty

A certificate without a stated measurement uncertainty does not meet the requirements of ISO/IEC 17025. Check this field before accepting the document as valid.