22 analytical & laboratory EquipmEnt
➠
manufacturer’s application knowledge and services most of the measurement equipment manufacturers’
available. All these factors contribute to the actual user- calibration services and a considerable amount of
experience and operational success. commercial calibration services. Without accreditation
the competence of these services is not proven. The
Regular traceable calibration
competence should be confirmed by auditing the service.
One should always make sure that the data produced Each calibration service provider must maintain an
by the measurement equipment is reliable and accurate. effective traceability chain. The primary standard must
Periodic calibration is absolutely essential. Typical be calibrated at an outside laboratory and then used for
calibration intervals can be viewed in Table 1. calibrations. Some commercial calibration services do
Table 2 presents an example of a traceability chain for not include uncertainty estimations in their calibration
installed humidity and temperature units. From a global certificates if not ordered separately. Some calibration
perspective, all measurements are based on the globally services are not able to calculate uncertainty at all. One
agreed International System of Units (SI). This ensures should always consider the competence of these services.
that we use the same quantities, and that measurements Laboratory calibration is preferred to field calibration.
performed with various types of equipment in various In a laboratory, the effects caused by the environment
locations are comparable. can be minimised, and the number of factors influencing
National laboratories are responsible for maintaining the calibration are reduced significantly.
and developing traceability and for providing the highest Field calibration is a quick and easy way of checking
accuracy calibrations. The services of the National measurement equipment without having to remove
Measurement Standard Laboratories may be limited to it from the process or process area. Field calibration
calibration of the highest grade primary standards. requires a working standard as a reference. This working
Commercial calibration services provide calibration standard can be hand-held or some other equipment
services for lower level standards and measurement used for calibrating the instrument installed in the
equipment. These may be manufacturer services process. Working standards are calibrated at a higher
providing calibration services for their own products, level laboratory. u
or laboratories providing calibration services for any
measurement equipment. Non-accredited calibration Daisuke Fujisawa is Regional Market Manager with Vaisala,
services are the majority service providers, including Tokyo, Japan. www.vaisala.com
circle 22 or ✔ at www.scientistlive.com/elab
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