Have you ever wondered what the key elements are
that you should look for on a calibration certificate ?
Or what it all means and why it could be significant to you ?
This article provides the answers to those questions with examples
from a typical certificate and extracts from its associated measurement
report.
| Feature |
Significance |
Example |
| Supplier's contact details |
Tells you who is responsible for the service.
Essential if you have a query about the calibration. |
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|
| Service type |
Most suppliers offer a variety of service
levels with different attributes. Should agree with your order. |
|
| Unique tracking and/or certificate number |
The supplier's key to all their records. A crucial aspect
of traceability. |
|
| Equipment identification |
Calibrations relate to an individual item
of equipment, not a product sample. |
|
| Customer identification |
If your equipment was subcontracted, your supplier will be
the customer, perhaps indicating that it was on your behalf. |
|
| Test location |
Identifies whether it was performed
at he customer's premises ("on-site" and perhaps in-situ
which may limit the scope of testing), the supplier's particular
branch or depot, or if a subcontractor was used. Measurements
made by a subcontractor may or may not be transparent to the
end-customer so it's wise to seek assurances about your supplier's
policy. |
|
| Test date |
Some calibrations take more than 1 day so will generally be
the calibration end-date. The date from which users determine
the next due calibration. |
|
| Test conditions |
Temperature, humidity and sometimes altitude
(pressure) are most often found as they can affect equipment
characteristics. A single value without control limits is meaningless. |
|
| Test methodology |
Reference to a documented procedure is an aspect of traceability.
Like the record of calibration standards used, it enables precise
repetition of the test in case of query. |
|
| Standards conformity |
Affirmation of compliance with, or independent
certification against, international conformity assessment standards
such as ISO9001 or ISO17025. May be service level dependent. |
|
| Performance summary |
A statement that clearly indicates whether
the equipment was met stated criteria or not, upon receipt and
at completion of calibration. May include concise details of
tests that failed to meet defined criteria. May be service
level dependent. |
|
| Scope of testing |
Indication of the tested functions and their
status, maybe in conjunction with a measurement report. Should
particularly identify significant omissions from manufacturer's
recommendations (if any) or known user requirements. |
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|
| Confidence level |
Concerns the likelihood that a spec compliance determination
is correct and relates to the uncertainty (or adequacy) of measurement.
By international agreement this is generally 95% (coverage factor
of 2) but may require higher or accept a lower probability if
the risk tolerance is higher in your application. |
|
| Acceptance limits used of reference publication |
Often citing a published specification,
it enables confirmation that the appropriate criteria was used
for your particular application. |
|
| Print or issue date |
If amendments are later found necessary, a later issue date
should appear to maintain a chronological paper trail. |
|
| Page numbering |
Have you received the complete records? |
|
| Details concerning traceability to international measurement
standards |
Usually an affirmation concerning the national metrology institutes
to which, ultimately, the supplier's calibration standards can
be related through an "unbroken chain of comparisons of stated
accuracy". |
|
| Measured values, particularly for non-conforming
tests |
Necessary if correctional data is to be
used and also for testpoints that fail to meet specification.
The degree of deviation is needed to establish whether re-work
or product recall is necessary if integrity has been compromised.
May be service level dependent. |
|
| Clarity of acceptance (or spec) limits and measured values |
Is it easy to verify the equipment's status? It is if measured
values and test limits are in the same format and units. The
measurement resolution must be appropriate to the test limit
resolution. |
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