Calibration is the documented comparison of a measurement device to be calibrated with a traceable reference.
All sensors and measurement devices must be calibrated prior to use in a validation study. Calibration results must be documented. Achievable measurement uncertainties must align with application-specific requirements.
- According to ISO/IEC GUIDE 99:2007, calibration is a process that establishes a relationship between measurement quantities and corresponding indications.
- Calibration = determined difference between the measured value and the true value (traceable reference/standard).
- Adjustment = correction of the measured value towards the true value to minimize measurement error and increase accuracy.
- Calibration & adjustment occur throughout the lifetime of a system, instrument, sensor, and must be performed.
- It is part of qualification and validation but does not replace them.
- It includes all sensors and measurement quantities, instruments, or a system, and defines the overall accuracy of the entire measurement chain.
- It refers to the performance and characteristics of sensors, measurement systems, and software.
- It includes general methods of metrology:
- Definition of the measurement method (environmental conditions; required standards method)
- Creation of a mathematical model for calibration assessment, including its measurement uncertainty
- Performance of the calibration
- Creation of a calibration certificate with details (determined deviation, adjustment, and measurement uncertainty)
- Depending on the process/sensor/measurement quantity, a post-calibration without adjustment is required for verification and documentation purposes after use.