A measuring instrument (or aggregate of mass) is set and adjusted in such a way that the measurement errors are as small as possible, or that the sum of the measurement errors does not exceed the error tolerances. Adjustment, therefore, requires an intervention that permanently changes the measuring instrument or aggregate of mass.
Calibration is the determination of a measurement error between the value indicated by the test specimen and that indicated by a standard or a standard measuring device.
(German accreditation body)
International Laboratory Accreditation Cooperation
- Infrared measurement
Above absolute zero (-273.16°C), all bodies emit energy in the form of electromagnetic radiation, so-called heat radiation. At low temperatures the wavelengths of this radiation are entirely within the infrared range and hence invisible to the human eye, which is why this form of temperature measurement is known as infrared thermometry. With increasing temperature, the wavelength of this radiation becomes shorter, and it is perceived from about 550°C as a dark red glow with the naked eye. As temperature increases further, the glow becomes stronger and, passing through light-red and yellow, white heat is reached at about 1300°C.
IR thermometers measure the intensity of this radiation, and the temperature of objects can be determined very quickly and conveniently. The big advantage of this method is that no contact with the measured object is necessary, i.e. there is no transfer of heat from a hot object to a colder temperature sensor, which, firstly, takes time and, secondly, may cause measurement inaccuracy. Inaccessible or moving objects can also be measured conveniently and very quickly, and under certain circumstances through windows.
A very important point for infrared thermometry is the so-called emission factor. This determines how "effectively" a body emits radiation. The ideal is the black body with an emission factor approximating to 1.0. The radiation emitted by a black body is exclusively thermal radiation.
Bodies with an emission factor also have portions of their radiation caused by reflexion or transmission. If one wishes to measure the temperature of such a body with an IR thermometer, precise knowledge of this emission factor is necessary. This can be set on the majority of instruments available on the market. The emission factor depends among other things on the material, surface characteristics, temperature and wavelength, and approximate values can be obtained for many applications from the available tables.
At LSM, IR thermometers are calibrated exclusively with black bodies in a cavity that satisfy the requirement of an emission factor of 1.0. For temperatures between -20°C and +350°C, these black bodies are maintained at a very even temperature by a constantly circulated liquid. For higher temperatures up to 1550°C, the radiation is emitted by black bodies accommodated in isothermal housings.
- Measuring tolerances
What is given is the extended measurement uncertainty yielded by the standard measurement uncertainty multiplied by the extension factor k=2. It was determined in accordance with DKD-3. The value of the measured variable is within the assigned value range with 95% probability.
(Internationales Wörterbuch der Metrologie, 2. Auflage 1994 3.9)
- National Standards
A Standard that, by national decree, is recognised in a country as the basis for determining the values of all other Standards of the measurement value in question.
(Internationales Wörterbuch der Metrologie, 2.Auflage 1994, 6.3)
- Official verification
The official verification of a measuring instrument (or aggregate of mass) incorporates the tests to be carried out by the responsible verification authority, in accordance with the verification specifications, and the seal.
By this testing, it is determined whether the measuring instrument submitted complies with the verification specifications, that is whether it satisfies the demands to be placed on it in terms of its qualities and technical measurement characteristics; and in particular it is verified that the sum of measurement errors does not exceed the error tolerances.
By means of the seal it is certified that, at the time of testing, the measuring instrument satisfied these requirements and that, due to its qualities, it is to be expected that it will remain within the indicated tolerance range throughout the verification validity period, if operated in accordance with the rules of technology. Law regulates those measuring instruments that require compulsory verification and those that are exempt.
- Reference standard
(Internationales Wörterbuch der Metrologie, 2. Auflage 1994, 6.6)
Standard, in general of the highest precision available at a considered location or an organization from which measurements are derived there.
- Service Standard
A Standard that is routinely used to calibrate or test aggregates of mass, measuring instruments or reference materials.
(Internationales Wörterbuch der Metrologie, 2. Auflage 1994, 6.7)
- Smallest Possible Measurement Uncertainty (DKD)
The measurement uncertainty assigned to a laboratory as the smallest possible measurement uncertainty for each measurement value and determined measurement ranges, on the basis of the assessment of the measurement uncertainty budget and, if applicable, comparative measurements carried out.
- Traceability (DKD)
A procedure to refer measurement results to national and international standards through an unbroken chain of calibrations.
- Water triple point cells
Water triple point cells from Ludwig Schneider are filled with high-purity water. This water is gas-free and has the same isotope composition as ocean water. Before filling, the cells are chemically cleaned with a special cleaning procedure. This is the reason for the low drift of this type of cell, which is less than 0.01 mK/a. Water triple point cells are maintenance-free and are mainly used for the calibration of platinum resistance thermometers.
Brochure: Water triple point cells