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    Frequently Asked Questions
  1. Why do I need to calibrate my instruments?

  2. Who is N.I.S.T.?

  3. Why is it necessary to recalibrate instruments at regular intervals?

  4. Why do I need to calibrate a brand new instrument with a warrantee?

  5. Which Company should I choose to carry out my calibrations?

  6. What are ISO 9000 series Quality Programs?

  7. What is meant by traceability?

  8. What should an excellent Certificate of Calibration contain?

1. Why do I need to calibrate my instruments?
Any instrument that is used to measure a physical parameter has certain accuracy. This means that over a period of time it is possible to experience a certain amount of drift, which will result in erroneous readings if the instrument is used to measure this parameter.

Calibration of instruments at regular intervals is the most satisfactory method of ensuring top performance for any instrument.


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 etc.

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


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