2. Who Is N.I.S.T.?
Every Country has a government body that controls the measurement standards,
and has in its possession the ultimate standards of physical parameters,
such as dimensional parameters, electrical parameters, optical parameters
In the UK for instance
N.P.L. (National Physics Laboratory)
carries out the task.
In the USA,
N.I.S.T. (National Institute
of Standards and Technology) carries out this task ensuring that via
correct calibration all similar instruments measure the same parameter producing
the same reading within their capabilities. The process is very similar
to ensuring that every choirboy sings from the same hymn sheet!
3. Why is it necessary to
recalibrate instruments at regular intervals?
If an instrument is used regularly, its repeatability and accuracy may
deteriorate, by passage of time. In addition as various parts of the instrument
age differently many will need realigning and readjusting.
Calibrating the instruments at regular intervals
and retention of all the previous certificates ensures that all these trends
are observed and that the behavior of the instrument remains predictable.
4. Why do I need to calibrate
a brand new instrument with a warrantee?
Even though Instruments come of the production line reasonably accurate
in their measurements, they are not certified and there is this doubt about
the traceability of the measurements performed.
5. Which Company should I
choose to carry out my calibrations?
There are many companies from very small operations to Multinationals.
The bigger they are not necessarily means the better they are. Look at their
certificate and see how much detail you get. When comparing prices always
compare like for like. A certificate that declares, “We certify that
this instrument is OK” is not worth the paper it has been written on. On
the other hand you may have to pay a considerable amount more to get a reasonably
detailed certificate, which add to the value of the instrument as they represent
a history of the stability and accuracy.
6. What are ISO 9000 series
of Quality Assurance Programs?
In Europe towards the late seventies a movement started to ensure that
standards were made uniform so that Germans could for example produce bolts
to fit French nuts and that say British cars could use the German bolts
and French nuts to assemble their cars. This gave rise to a system of paperwork
and standards, that ensured a total traceability of the origins of not only
the raw materials to final product, but also from a customer’s enquiry to
final delivery. This system of paperwork is defined as
ISO 9001 or
ISO 9002 depending upon the type of Company, seeking the approval.
These days in Europe many large manufacturers
prefer to purchase from Companies with these approvals. One of the requirements
of these programs is the regular calibration program of used instruments
within the approved Company.
7. What is meant by traceability?
When a company calibrates your instrument they use more accurate instrument
than yours to verify the performance of your instrument. They also on a
regular interval have to send their equipment to another Company who has
in their possession a more accurate instrument than your supplier’s and
so on. The chain carries on until the ultimate, which is N.I.S.T.
If your instrument hasn’t got an
N.I.S.T. traceable certificate
there is no guarantee that the calibration is valid because the chain should
never be a broken one.
8. What should an excellent
Certificate of Calibration contain?
Name and address of Customer
Instrument and the type
Instrument Serial Number
Date Of Test
Date of next Test
Equipment used to carry out the calibration and serial numbers
Interpretations of the figures
Statement of confidence probability
Statement of traceability
Ambient temperature at the time of calibration (If On Site)
Signature of calibration Engineer