Policy on the Traceability
of Measurement Results
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Effective Date 2015-10-29
Reviewed by: Araya Fesseha
Approved by: Mr. Mahamouda Ahmad Gaas
Position:
Position: Accreditation Council Chairman
Director General
Signature:
Contents
Signature:
page
1.
Purpose and scope ............................................................................................................................ 2
2.
References .......................................................................................................................................... 2
3.
Responsibility ...................................................................................................................................... 2
4.
Terms and abbreviations................................................................................................................... 2
Terms ............................................................................................................................................... 2
4.1.
4.2.
5
Abbreviations: ............................................................................................................................. 3
Traceability Policy .............................................................................................................................. 3
Policy on the Traceability
of Measurement Results
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1. Purpose and scope
This policy document details the traceability requirements of ENAO and acceptable traceability
terms for CABs. This document is applicable for all conformity assessment bodies (CABs)
accredited under ENAO accreditation Program.
2. References
ILAC P10:2013:- ILAC Policy on the Traceability of Measurement,
International vocabulary of metrology – Basic and general concepts and associated terms (VIM)
ILAC P14:2013 ILAC policy for uncertainty in calibration
3. Responsibility
It is the responsibility of Accreditation Director and Respective Team for the implementation of
this policy.
4. Terms and abbreviations
4.1.
Terms
Metrological traceability: - is the property of a measurement result whereby the result can be
related to a reference through a documented unbroken chain of calibrations, each contributing
to the measurement uncertainty (VIM: 2010).
Reference Standard: - The standard used to calibrate the working standard (e.g., reference
thermometers, masses). These shall be calibrated externally.
Working Standard: - Routinely used to verify measuring instruments or measuring systems
(e.g., working thermometers).
Reference Material (RM):- Material or substance one or more of whose property values are
sufficiently homogeneous and well established to be used for the calibration of an apparatus,
the assessment of a measurement method, or for assigning values to the materials. (ISO/IEC
Guide 43-1)
Certified Reference Material (CRM):- A Reference Material accompanied by documentation
issued by an authoritative body and providing one or more specified property values with
associated uncertainties and trace abilities using valid procedures.
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Critical equipments:-equipments used for direct measurement of measurand reported or
measurand to be directly/indirectly used in calculation of result to be included in a report /
certificate.
Appropriate NMIs/Calibration laboratories:-those NMIs defined in option 1 or Calibration labs
as in option 2 otherwise proven to be competent sources of traceability for cases of options
3A/3B.
4.2.
Abbreviations:
BIPM: international committee for weight and measures
BMC: best measuring capability
CABs: conformity assessment bodies
CIPM: international committee for weight and measures
CMC: calibration measuring capability
ILC: Inter laboratory comparison
KCDB: key comparison data base
MRA: mutual recognition arrangement
NMI: National metrology Institute
RMPs: reference material producers
5
Traceability Policy
5.1. ENAO accredited/ Applicant Conformity assessment bodies (CABs) are required to have an
established calibration program of critical equipments, reference standards, and hence the
measurement results generated by that equipment, relevant to their scopes of accreditation, are
traceable to the International System of Units (SI units) through appropriate a National
Metrology Institute (NMI) ,other Metrology bodies or calibration laboratories via an unbroken
chain of comparisons as detailed below.. Therefore all equipment used by ENAO accredited
CABs including equipment for subsidiary measurements (e.g., for environmental conditions)
having a significant effect on the accuracy or validity of the test/calibration result (e.g.,
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significant contributor to overall CABs services uncertainty, etc.) shall be calibrated before being
put into use. Moreover when traceability to SI units is not possible or practical ENAO
accredited/applicant CABs shall insure traceability of RMs To CRMs from acceptable sources,
where applicable RMPs that have accredited/implemented ISO guide 34:2009.
5.2. Metrological traceability can be demonstrated by having calibrations performed by
appropriate NMIs/Calibration laboratories. These calibration services specifically shall be
obtained from the following four alternative sources of traceability.
I) NMI whose service is suitable for the intended calibration and is covered by the
CIPM MRA which can be viewed in Appendix C of the BIPM KCDB or
II) An accredited calibration laboratory whose service is suitable for the intended need (i.e., the
scope of accreditation specifically covers the appropriate calibration range) and the
Accreditation Body is covered by the ILAC Arrangement or by Regional Arrangements
recognized by ILAC.
IIIa) NMI whose service is suitable for the intended need but not covered by the CIPM MRA
with demonstrated competence as described or.
IIIb) A calibration laboratory whose service is suitable for the intended need but not covered by
the ILAC Arrangement or by Regional Arrangements recognized by ILAC with demonstrated
competence as described.
In cases where traceability is established through either IIIa) or IIIb) , ENAO insures that the
following appropriate evidence of technical competence is verified and documented for non
accredited calibration laboratories and NMI Non MRA signatory to CIPM and/or range and
uncertainties not published on appendix C of BIPM KCDB .
This
evidence for the technical competence of the laboratory and claimed metrological
traceability is likely to include but not limited to the following: Records of calibration method validation
 Procedures for estimation of uncertainty
 Documentation for traceability of measurements
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 Documentation for assuring the quality of calibration results
 Documentation for competence of staff
 Documentation for accommodation and environmental conditions
 Audits of the calibration laboratory
The choice of route IIIa) or IIIb) is unlikely to be made on purely economic grounds, and is more
likely to be a last resort if other routes are unavailable, as the first two alternatives are best
alternatives in traceability.
ENAO accredited calibration laboratory or NMI evaluated by ENAO or laboratory evaluated by
ENAO for proving technical competence shall be considered as evidences for option IIIa and
IIIb.
when traceability to SI units is not possible or practical ENAO accredited/applicant CABs shall
insure traceability of RMs by using
 certified reference materials from accredited Reference Material Producers (RMPs),
where available, and practicable
 Accredited laboratories may perform internal calibrations for their own working
instruments provided:
 The laboratory has documented procedures for this internal calibrations task;
 The laboratory reference instrument/standard from which traceability is derived, has
been calibrated by an accredited calibration laboratory or NMI; and,
 Training records must be maintained for staff performing calibrations and these records
must demonstrate the technical competence.
 ENAO also recognize traceability to specified methods and /or consensus standards that
are clearly described and agreed by all parties concerned. The laboratory shall provide
satisfactory evidence of correlation of results for example by participating in inter
laboratory comparison (ILC), Proficiency Testing and/ or performance characteristics
checks against manufacturer’s standards.
5.3. The laboratory calibration program shall specify frequency of re-calibration. The frequency
of re-calibration is dependent on many factors (e.g., whether it is a reference standard,
frequency of use, stability, etc…). Although the frequency of re-calibration may be extended, it
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cannot be eliminated.
5.4. When using an external calibration service to comply with this policy, the calibration
laboratory used must be accredited/proven competent using ISO/IEC 17025:2005 and provide
an appropriate calibration certificate. When looking at the calibration certificate the following
things should appear on the certificate:
- An indication that the calibration laboratory is accredited to ISO/IEC 17025:2005 by a ILAC
recognized and named accreditation body ;
-The serial number of the measuring equipment (or reference standards) being used to calibrate
CAB’s equipment and
- A statement that the measuring equipment (or reference standard) is traceable to SI units
5.5. If newly purchased measurement equipment is provided with/without an appropriate
calibration certificate, its calibration shall be performed prior to use.
5.6. Instruments that drift, or are prone to sudden changes in precision or measurement
capability, requires periodic verification/intermediate check. The verifications/intermediate shall
be appropriate to the range of the use of the instrument.
Note:-Verification does not establish traceability. It is not a method of propagating uncertainties,
which is the core issue in a calibration. Verification seeks only to determine whether or not the
instrument is operating within its expected tolerances. Tolerances are not always the same as
uncertainties.
For these types of instruments that require verification/intermediate check, the laboratory must
have verification/intermediate check procedures that detail:
 How to conduct verification /intermediate check,
 The frequency of verifications;
 The acceptance criteria; and,
 Actions taken when the acceptance criteria are not met (e.g., recall of data, etc.)
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of Measurement Results
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Date approved
Revision History
2015-05-20
The title of the document was changed to Policy on the
Traceability of Measurement Results
Clause 3 was revised to include responsibility for the
implementation of this document.
Clause 4.8 was revised to make more clear how ENAO
handle the options to accept metrological traceability from
accredited labs which are not covered by ILAC MRA or from
NMIs which are not covered by CIPM MRA.
Clause 4.8 was removed to make more clear how ENAO
handle the options to accept metrological traceability from
accredited labs which are not covered by ILAC MRA or from
NMIs which are not covered by CIPM MRA with conditions of
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similar to annex A on ILAC P10.
Clause 4.2 was revised to describe routes of metrological
traceability specially how it can be verified for non accredited
CAL labs and non MRA signatory NMIs
Acronyms and definition of terminologies added to clarify and
make document self explanatory.