Calibration is the comparison of measurement values delivered by a device under test with those of a calibration standard of known accuracy. Such a standard could be another measurement device of known accuracy, a device generating the quantity to be measured such as a voltage, a sound tone, or a physical artifact, such as a meter ruler.
A calibration laboratory establishes whether the value given by a measuring instrument is correct in relation to the international unit of measurement. An ISO-17025 accreditation offers the best guarantee that this is indeed the case. Accreditation is granted for a specific area of work based on a specific, defined method. In accreditation, this is called the 'scope'.
Each European country has its own accrediting body. These organisations have a so-called Mutual Recognition Agreement (MRA) with each other, in Europe, and often beyond. In Europe there is an umbrella organisation called the European Cooperation for Accreditation (EA). This organisation ensures that accreditation is dealt with in the same way in all countries and that the same requirements apply everywhere. Certificates issued under accreditation in all these countries are therefore fully recognized and accepted in countries that have signed the MRA.
A guarantee of flawless work can never be given. Accreditation guarantees that "work is performed with the highest possible reliability". In order to continue to test this reliability, audits are carried out, with some regularity internal audits and at least once a year an external, independent audit is carried out by the accrediting body. Accredited laboratories are obliged to participate in proficiency testing, studies in which the test results of different laboratories are compared with each other.
The calibration of a blower door consists of 2 parts: a pressure calibration and a flow calibration. It is always recommended to make sure how these calibrations are performed. What kind of measurement setup is used and what are the measurement points? The scope (measured quantities, measuring method, ranges and uncertainties) of accredited labs can be found on the internet.
- Directory of EA Members and MLA signatories – European Accreditation
International Organization for Standardization,"ISO/IEC 17025: 2017. General requirements for the competence of testing and calibration laboratories", 2017.