The purpose of controlling the environment of the metrology laboratory is to subdue whatever disturbances seriously affect the intended work. The elements of the environment which require some degree of control and typical constraints are: Table 1. Metrology Laboratory Environmental Control Specifications Temperature level usually 20°, 23° or 25°C Temperature constancy from ±0.01° to ±2°C Temperature uniformity from 0.02° to 2°C Relative humidity 35% to 55% Pressure 5 to 10 mm W.C. gage Lighting 50 to 100 foot candles Cleanliness < 1 million particles over one micron size per cubic meter air Noise 35 on noise criteria curve from 20 to 9,600 Hz Electrical fields avoid RF interference and magnetic masses. Vibration <50 nM displacement below 200 Hz at instrument base. These limitations are included in standards which are still a matter of discussion. Of these - temperature excursion and vibration cause the greatest concern. Special notice is made of vibration - the constraint on which there appears to be least agreement. Selected design efforts are described to illustrate the wide range of solutions to these problems and the difficulty of arriving at a consensus on standards for environmental control.
H. L. Daneman, H. L. Daneman,
"Environmental Control of the Metrology Laboratory", Proc. SPIE 0732, 1st Intl Conf on Vibration Control in Optics and Metrology, (26 August 1987); doi: 10.1117/12.937907; https://doi.org/10.1117/12.937907