A calibration certificate is the proof that an instrument was tested against a known reference. Auditors, customers and quality managers rely on it, so it is worth knowing what a good one contains.
What is normally on a certificate
Requirements vary by laboratory and standard, but a complete certificate typically includes:
- a title and a unique certificate number;
- the name and address of the laboratory, and where the calibration was done (on site or in the laboratory);
- the customer’s name;
- a clear description and unique identification of the instrument, such as make, model and serial number;
- the dates the item was received (where relevant), calibrated and the certificate issued;
- the calibration method or procedure used;
- the results, with units, and the measurement uncertainty;
- a statement of metrological traceability to national or international standards;
- the environmental conditions where they affect the result;
- the name and signature, or equivalent authorisation, of the person approving the certificate;
- a statement of conformity with a specification, where one was agreed.
“As found” and “as left” results
“As found” results show how the instrument was performing when it arrived. “As left” results show how it performed after any adjustment. As-found data matters because it tells you whether earlier measurements could have been affected.
Measurement uncertainty
No measurement is perfect. The uncertainty tells you how much doubt there is in each result. For the certificate to be useful, the uncertainty should be small compared with the tolerance you need to work to.
Accredited and non-accredited certificates
If the laboratory is accredited for the calibration, for example by NATA in Australia, the certificate usually carries the accreditation body’s endorsement and refers to the accredited scope. Some customers and standards require an accredited certificate, so confirm what your situation needs before booking.
What to check when you receive one
- The instrument ID and serial number match the item.
- The range and units cover the way you use the instrument.
- The results are within your tolerance, allowing for the stated uncertainty.
- The calibration date is recorded in your register, with the next due date set by your procedure.