Calibration and Measurement Capabilities (CMC's) are metrological traceable to the International System of Units (SI) through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty.
The laboratory's specific measurement capabilities are certified by the NRC's Calibration Laboratory Assessment Service (CLAS) and accredited by the accreditation body in accordance with the following definitions:
Type I: A capability of which the primary purpose is the calibration of measurement standards for other calibration laboratories. A laboratory with this type of capability has the appropriate reference standards, working standards, check standards, and calibration systems to be able to assess dynamically and to quantify its measurement uncertainty, and is able to monitor its measurement processes continually. The environmental conditions that affect the laboratory's measurements are closely monitored and controlled. A laboratory with this type of capability usually reports a measurement value accompanied by a comprehensive statement of measurement uncertainty. A laboratory with this type of capability is often referred to as a standards or standards calibration laboratory.
Type II: A capability of which the main purpose is the calibration and adjustment of test, measurement and diagnostic equipment for use in product testing, manufacturing, servicing, etc. A laboratory with this type of capability has the appropriate working standards and calibration systems to be able to calibrate to a manufacturer's specification and tolerance or calibrate to a written standard, using appropriate test uncertainty ratios (TUR). A laboratory with this type of capability usually reports a measurement value and indicates if the test equipment complies with a specification, tolerance or a written standard. It will, usually, base its capabilities on the specifications and tolerances of the working standards being used. It also has, normally, the means to check its working standards between calibrations and has available the appropriate environment(s). A laboratory with this type of capability is often referred to as a test equipment calibration laboratory.
Type III: A capability, within a laboratory, mobile or fixed, with the appropriate reference or working standards, of which the main purpose is to provide a reference. A laboratory with this type of capability usually has minimal means to monitor its calibration system. It relies mainly on the values assigned by higher echelon laboratories to its standards and uses these values with few other considerations to assign values or verify the compliance of equipment being calibrated to their specifications and tolerances or to written standards. This could be an on-site service subject to a wide range of environmental factors.
The calibration and measurement capabilities of the laboratory are expressed in terms of:
Measure or reference material;
Measurement range;
Additional parameters where applicable, e.g. frequency of applied voltage;
Measurement uncertainty;
Calibration or measurement method or procedure; and
Type of instruments or materials to be calibrated or measured.
The measurement uncertainty associated with a measurement in a CMC is an expanded measurement uncertainty with a level of confidence of approximately 95 %, typically using a coverage factor of k = 2. However, laboratories may report a coverage factor different than k = 2 to achieve the 95 % level of confidence. The measurement uncertainties quoted do not include the possible effects of transportation, long term stability or intended use of the calibrated device. The measurement uncertainty of a specific calibration by the laboratory can be greater than the CMC because it will include uncertainties due to the actual condition and behaviour of the customer's device during its calibration.
Accreditation is the formal recognition of specific calibration capabilities. Neither the NRC nor the accreditation body guarantee the accuracy of individual calibrations by the laboratory.
Where the measured quantity includes a range and the measurement uncertainty also includes a range, the first value in the measured quantity range corresponds to the first value in the measurement uncertainty range. Similarly for the second value in the measured quantity range and measurement uncertainty range. The measurement uncertainty can be assumed to be linear function of the measured quantity.
Where the remarks column directs the reader to an Annex the measurement uncertainty given in the body of the CLAS Certificate is not a linear function of the measured quantity. The measurement uncertainties stated are the minimum and maximum uncertainties throughout the range. The reader should consult the Annex for their specific needs.
