ISA TR52.00.01

The usual concept that working standards are less accurate than reference standards and that the environmental requirements are less demanding is the basis for this technical report. The same concept carries over, in general, in differentiating between Type I and Type II laboratories. It should be emphasized that this technical report is intended to apply to Echelon II laboratories only (see Clause 3). Moreover, this technical report serves primarily as a guideline to the design, construction, and operation of standards laboratories and, thus, is not to be construed as mandatory requirements. In many cases satisfactory repeatability of calibrations can be obtained even though the environment does not comply fully with this technical report.

For additional information, see ISAO/R 554, Standard Atmospheres, NCSL RP-7, Laboratory Design, and NCSL RP-14, Guide to Selecting Standards-Laboratory Environments.

Purpose

The measured value assigned to a standard or measurement instrument has the essential qualification that the assigned value was valid at the specific time and under the specific conditions of the calibration. No assurance is made regarding the future value or the value under different conditions. If the device is physically stable with time, and if a sufficient history is compiled under environmental conditions that are compatible with the previous calibration, the confidence level of the assigned value increases. If the specific conditions of measurements are not repeated when the device is again calibrated, any variables introduced can create substantial uncertainty. With this fact in mind, it is obvious that there is a need for knowing and maintaining the environmental factors associated with the various types of measurement standards and instruments. Aside from the necessity of securing repeatable measurements, environmental controls help to reduce the number of tedious corrections necessary in making measurements that are affected by adverse environments.