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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Calibration | 3/4 | https://en.wikipedia.org/wiki/Calibration | reference | science, encyclopedia | 2026-05-05T14:27:46.942283+00:00 | kb-cron |
An automatic pressure calibrator is a device that combines an electronic control unit, a pressure intensifier used to compress a gas such as Nitrogen, a pressure transducer used to detect desired levels in a hydraulic accumulator, and accessories such as liquid traps and gauge fittings. An automatic system may also include data collection facilities to automate the gathering of data for record keeping.
=== Process description and documentation === All of the information above is collected in a calibration procedure, which is a specific test method. These procedures capture all of the steps needed to perform a successful calibration. The manufacturer may provide one or the organization may prepare one that also captures all of the organization's other requirements. There are clearinghouses for calibration procedures such as the Government-Industry Data Exchange Program (GIDEP) in the United States. This exact process is repeated for each of the standards used until transfer standards, certified reference materials and/or natural physical constants, the measurement standards with the least uncertainty in the laboratory, are reached. This establishes the traceability of the calibration. See Metrology for other factors that are considered during calibration process development. After all of this, individual instruments of the specific type discussed above can finally be calibrated. The process generally begins with a basic damage check. Some organizations such as nuclear power plants collect "as-found" calibration data before any routine maintenance is performed. After routine maintenance and deficiencies detected during calibration are addressed, an "as-left" calibration is performed. More commonly, a calibration technician is entrusted with the entire process and signs the calibration certificate, which documents the completion of a successful calibration. The basic process outlined above is a difficult and expensive challenge. The cost for ordinary equipment support is generally about 10% of the original purchase price on a yearly basis, as a commonly accepted rule-of-thumb. Exotic devices such as scanning electron microscopes, gas chromatograph systems and laser interferometer devices can be even more costly to maintain. The 'single measurement' device used in the basic calibration process description above does exist. But, depending on the organization, the majority of the devices that need calibration can have several ranges and many functionalities in a single instrument. A good example is a common modern oscilloscope. There easily could be 200,000 combinations of settings to completely calibrate and limitations on how much of an all-inclusive calibration can be automated.
To prevent unauthorized access to an instrument tamper-proof seals are usually applied after calibration. The picture of the oscilloscope rack shows these, and prove that the instrument has not been removed since it was last calibrated as they will possible unauthorized to the adjusting elements of the instrument. There also are labels showing the date of the last calibration and when the calibration interval dictates when the next one is needed. Some organizations also assign unique identification to each instrument to standardize the record keeping and keep track of accessories that are integral to a specific calibration condition. When the instruments being calibrated are integrated with computers, the integrated computer programs and any calibration corrections are also under control.
== Historical development ==
=== Origins === The words "calibrate" and "calibration" entered the English language as recently as the American Civil War, in descriptions of artillery, thought to be derived from a measurement of the calibre of a gun. Some of the earliest known systems of measurement and calibration seem to have been created between the ancient civilizations of Egypt, Mesopotamia and the Indus Valley, with excavations revealing the use of angular gradations for construction. The term "calibration" was likely first associated with the precise division of linear distance and angles using a dividing engine and the measurement of gravitational mass using a weighing scale. These two forms of measurement alone and their direct derivatives supported nearly all commerce and technology development from the earliest civilizations until about AD 1800.
=== Calibration of weights and distances (c. 1100 CE) ===
Early measurement devices were direct, i.e. they had the same units as the quantity being measured. Examples include length using a yardstick and mass using a weighing scale. At the beginning of the twelfth century, during the reign of Henry I (1100-1135), it was decreed that a yard be "the distance from the tip of the King's nose to the end of his outstretched thumb." However, it wasn't until the reign of Richard I (1197) that we find documented evidence.
Assize of Measures "Throughout the realm there shall be the same yard of the same size and it should be of iron." Other standardization attempts followed, such as the Magna Carta (1225) for liquid measures, until the Mètre des Archives from France and the establishment of the Metric system.