What is a calibration certificate?
The calibration certificate constitutes evidence that demonstrates that the instrument has been calibrated, useful in those schemes, such as ISO 9000, in which the calibration of instruments of Measurement is a requirement.
A calibration certificate also constitutes evidence of the traceability of calibration results; that would be transferred to the user’s measurements if the respective uncertainty is associated with it.
What should a calibration certificate contain?
A calibration certificate must provide the information in an exact, clear, unambiguous and objective manner, and must include all the information agreed upon with the client and that necessary for the interpretation of the results and all the information required in the method used.
Each calibration certificate must include, at least, the following information:
- A title (for example, “Test Report”, “Calibration Certificate”, or “Sampling Report”).
- The name and address of the laboratory.
- The place where laboratory activities are carried out.
- A unique identification that all its components are recognized as a part of a complete report and a clear identification at the end of the certificate.
- The name and contact information of the customer.
- The identification of the method used.
- A description and identification of the calibrated instrument.
- The date of receipt of the calibrated instrument.
- The dates of execution of the laboratory activity and date of issue.
- The reference of the calibration method.
- A statement that the results relate only to the items undergoing calibration.
- The results with the units of measurement including the uncertainty of the resulting measurement.
- The identification of the people who authorize the report.
- A statement that identifies how measurements are metrologically traceable.
- Where relevant, a declaration of conformity with the requirements or specifications.
- Any other information agreed with the client.
What is a Calibration Certificate for?
- Deviation: The main benefit for a user is to use information about the measurement error (deviation) of the instrument readings relative to the standard to correct them, and ensure their traceability with an appropriate uncertainty.
- Uncertainty: The result of a measurement is incomplete without the expression of its uncertainty. The user must estimate the uncertainty of his measurement considering the relevant contributions, which must necessarily include that coming from the calibration, taken from the certificate, and combine them appropriately.
- Traceability: Traceability is the ability to relate the results of an individual measurement to national or international standards through an uninterrupted chain of comparisons, called the traceability chain, which would be transferred to the user’s measurements if the respective uncertainty is associated with it.
Who can issue or issue a Calibration Certificate?
Only calibration or testing laboratories accredited by an accreditation body. In our case, for Colombia, it is ONAC (National Accreditation Body of Colombia), which in turn is recognized internationally with agreements signed between member countries of regional and global accreditation cooperation and forums.
In 2010 ONAC was admitted as a member of the International Accreditation Forum – IAF and in 2013 it went from being an associate member to being a full member of InterAmerican Accreditation Cooperation – IAAC, being also elected as one of the members of its Executive Committee. Likewise, in that year, ONAC became an associate member of the International Laboratory Accreditation Cooperation – ILAC.
Given that the work carried out by ONAC is evaluated, in turn, by international peers, the calibration certificates of the Colombian OECs (accredited calibration and testing laboratories) have validity in multiple countries that are part of the international cooperation agreements in which ONAC is a part, agreements that are endorsed by peer evaluations, as long as the accreditation bodies demonstrate compliance with the requirements of the ISO/IEC 17011 standard “Conformity assessment. General requirements for accreditation bodies that carry out the accreditation of conformity assessment bodies.”
Who endorses the calibration certificates?
As mentioned above, the accreditation bodies of each country endorse the calibration certificates issued by each calibration or testing laboratory accredited by said bodies, and in turn they are endorsed by each international body thanks to international agreements.
What is the validity or validity of the calibration certificates?
Contrary to what one might initially think, calibration certificates are not valid. In fact, this document only represents the measurements of the instrument at the time it was calibrated and under the conditions in which it carried out that process; accredited calibration certificates will always have a note about this.
Considering that a calibration is the comparison between the measurements of the instrument to be calibrated and those of a standard, and assuming that the standard will always have the true value of a magnitude, if your measuring instrument can change over time, either due to wear of the components (both mechanical and electronic) typical of its normal use, due to the conditions of use that may arise to be extreme, because it has been repaired, among others, then the calibration must be repeated.
In general, all instruments tend to change over time, even if they are not in use, whether mechanical or digital. Taking into account the various factors that could influence a pressure gauge to present changes in its measurements, calibration periods must be established.
It is important to understand that the only one who has all the information required to determine this period is the owner, end user of the instrument.
Manufacturers provide recommendations in this regard that are very useful and should not be discarded without having solid evidence, since they estimate them through statistical processes evaluating large numbers of instruments of the same reference. Trusting the manufacturer’s recommendation will always be a good starting point.
This concept of establishing calibration periods and therefore a new calibration certificate is not new nor is it exclusive to a certain sector, on the contrary, highly qualified people and technical institutes have already faced this and have published their recommendations and procedures. Among the most notable we can name the ILAC P24 documents “Guidelines for the determination of calibration intervals of measuring instruments”, the OIML D10 “Guidelines for the determination of recalibration intervals of measuring equipment used in testing laboratories” and the NCSL RP1 “Establishment and Adjustment of Calibration Intervals”.