Preservation Environment Monitor
n. (PEM, abbr.)Equipment that monitors and records temperature and relative humidity and that can predict the effects of those changing conditions on the longevity of organic materials.
NotesThe monitor was developed by the Image Permanence Institute at the Rochester Institute of Technology.
CitationsIPI 2003 The PEM calculates and displays, in real time, values that reflect the decay rate of organic materials stored in that location. These values, known as Preservation Index (PI) and Time-Weighted Preservation Index (TWPI), show how temperature and humidity combine to influence the rate of decay processes such as paper discoloration, dye fading, deterioration of plastics, and textile embrittlement. The PEM displays PI and TWPI values alternately with temperature and RH on a 15-second cycle. Thus, no computer is needed to immediately determine the overall quality of storage conditions with respect to the 'natural aging' rate of all types of organic objects in collections.