Calibration capabilities are 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 Standards Council of Canada (SCC) 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 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 calibration 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 measurement capability of the laboratory includes the uncertainty associated with the calibration of the laboratory's reference or transfer standard by the NRC, or by a laboratory acceptable to CLAS, uncertainties caused by the transportation of the calibrated reference standard from the NRC (or other laboratories) to the laboratory, uncertainties of the calibration process in the laboratory, and uncertainties due to the behaviour of the most ideal available standard or measurement device for a specific measurement technology. These uncertainties include components which could have been evaluated by statistical methods on a series of repeated measurements and which can be characterised by experimental standard deviations. The other components, which can also be characterized by standard deviations, are evaluated from assumed probability distributions based on experience or other information. These have been combined to form an expanded uncertainty U = kuc with U determined from a combined standard uncertainty uc and a coverage factor k = 2. Since it can be assumed that the probability distribution characterised by the reported result and uc is approximately normal, the value of a calibrated device can be asserted to lie in the interval represented by the expanded uncertainty U with a level of confidence of approximately 95 percent. The uncertainties quoted do not include the possible effects on the calibrated device of transportation, long term stability or intended use.
The uncertainty of a specific calibration by the laboratory can be greater than the calibration measurement capability because it will include uncertainties due to the actual condition and behaviour of the customer's device during its calibration.
CLAS certification and SCC accreditation is the formal recognition of specific calibration capabilities. Neither the NRC nor SCC guarantee the accuracy of individual calibrations by the laboratory.
Where the measured quantity includes a range and the uncertainty also includes a range, the first value in the measured quantity range corresponds to the first value in the uncertainty range. Similarly for the second value in the measured quantity range and uncertainty range. The uncertainty can be assumed to be linear function of the measured quantity.
Where the remarks column directs the reader to an Annex the uncertainty given in the body of the scope is not a linear function of the measured quantity. The uncertainties stated are the minimum and maximum uncertainties throughout the range. The reader should consult the Annex for their specific needs.