The usual concept that working standards are less accurate thanreference standards and that the environmental requirements areless demanding is the basis for this technical report. The sameconcept carries over, in general, in differentiating between Type Iand Type II laboratories. It should be emphasized that thistechnical report is intended to apply to Echelon II laboratoriesonly (see Clause 3). Moreover, this technical report servesprimarily as a guideline to the design, construction, and operationof standards laboratories and, thus, is not to be construed asmandatory requirements. In many cases satisfactory repeatability ofcalibrations can be obtained even though the environment does notcomply fully with this technical report.
For additional information, see ISAO/R 554, StandardAtmospheres, NCSL RP-7, Laboratory Design, and NCSLRP-14, Guide to Selecting Standards-LaboratoryEnvironments.
Purpose
The measured value assigned to a standard or measurementinstrument has the essential qualification that the assigned valuewas valid at the specific time and under the specific conditions ofthe calibration. No assurance is made regarding the future value orthe value under different conditions. If the device is physicallystable with time, and if a sufficient history is compiled underenvironmental conditions that are compatible with the previouscalibration, the confidence level of the assigned value increases.If the specific conditions of measurements are not repeated whenthe device is again calibrated, any variables introduced can createsubstantial uncertainty. With this fact in mind, it is obvious thatthere is a need for knowing and maintaining the environmentalfactors associated with the various types of measurement standardsand instruments. Aside from the necessity of securing repeatablemeasurements, environmental controls help to reduce the number oftedious corrections necessary in making measurements that areaffected by adverse environments.
- Edition:
- 06
- Published:
- 01/01/2006
- Number of Pages:
- 37
- File Size:
- 1 file , 220 KB
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