HUMIDITY MEASUREMENT AND CONTROL IN CLEANROOMS.

This article explores some of the humidity concepts and instruments appropriate to cleanroom activities. No attempt has been made to provide complete details; more in-depth information can be found in the excellent publications prepared by the National Bureau of Standards, (NBS), ASHRAE, and others. It is shown that the selection of instruments for measuring and controlling humidity requires careful consideration so that unnecessary costs can be avoided. First, the humidity level and tolerances for the particular process must be determined. Next, the number of sensors needed and their placement within the room should be established, with the possibility of humidity fluctuations and excursions kept in mind. Sensor manufacturers' literature and specifications should be carefully reviewed, and questions should be asked concerning the reliability and stability of each sensor. The cost and inconvenience of sensor recalibration and replacements for maintaining the required tolerances must also be considered.