FAQ
Inquiries
Definition 1
Definition 2
Definition 1
Calibration is the comparison of instrument performance to a standard of known accuracy.
Definition 2
This definition is taken from the "Dictionary of Occupational Titles", an official guidebook produced by the Employment and Training Administration of the US Department of Labor.
"Develops and evaluates calibration systems that measure characteristics of objects, substances, or phenomena, such as length, mass, time, temperature, electric current, luminous intensity and derived units of physical or chemical measure. Identifies magnitude of error sources contributing to uncertainty of results to determine reliability of measurement process in quantitative terms. Redesigns or adjusts measurement capability to minimize errors. Develops calibration methods and techniques based on principles of measurement science, technical analysis of measurement problems and accuracy and precision requirements. Directs engineering, quality and laboratory personnel in design, manufacture, evaluation and calibration of measurement standards, instruments and test systems to insure selection of approved instrumentation. Advises others on methods of resolving measurement problems and exchanges information with other Metrologist personnel through participation in government and industrial standardization committees and professional societies."
• Increases production yields
• Optimizes resources
• Assures consistency
• Ensures measurements (and perhaps products) are compatible with those made elsewhere
And, by making sure that your measurements are based on international standards, you promote customer acceptance of your products around the world.
- National Standard.......................... Accurate to 0.002%
- Calibration Laboratory........................................0.01%
- Company "Master" Item.....................................0.07%
- Company Production Equipment.............................1.0%
- Produced Product..............................................10.0%
Of course, these calibrations need to be done on a planned, periodic basis with evidence of the comparison results maintained. This record must include identification of the specific standards used (which must be within their assigned calibration interval) and some means of knowing the method used and other test conditions. By examining these records, it should be possible to demonstrate an unbroken chain of comparisons that ends at the agency responsible for maintaining and developing a country's measurement standards (NIST). This demonstrable linkage to national standards, with known accuracy, represents "traceability".
In fact, it doesn't stop there because these laboratories routinely undertake international comparisons which help to establish worldwide consensus on the accepted value of the fundamental measurement units - without which, there would be little confidence in, for instance, successfully mating a 10 mm screw manufactured in one country with a 10 mm nut produced in another!
This refers to the calibration interval assigned to an item of equipment -- examples could be 3 months or perhaps 2 years. An alternative way of expressing this is the calibration cycle, usually how many calibrations are required per year. Equipment used in any Metrological situation must have known accuracy; that is, a specification assigned by the manufacturer or by the user. Since the performance of pretty much everything on Earth degrades with time, or use (or potential abuse), the expected accuracy must relate to a given period.
Of course, the higher the TAR, the better, but higher performance test gear or extended test times for averaging, for instance, costs more and the pursuit of an excessively high TAR is cautioned against.
