Realization of relative humidity scale from 10% to 98% at 25°C

Abstract

The accurate measurements of relative humidity are increasingly needed in most of the Egyptian industries. The relative humidity has its own effect in the manufacturing of medicine, steel, metals, textile and is of great importance for controlling the environmental conditions in the factories. As a result of the above facts, it was found that the realization of Egyptian humidity scale is of prime importance for National Institute for Standards (NIS). The scale was realized using two-pressure humidity generator and humidity chamber as a medium, chilled mirror hygrometer to measure dewpoint and RTD to measure air temperature. The relative humidity scale was realized in the range from 10% to 92% using two-pressure humidity generator [1] and from 92% to 98% using humidity chamber at 25ºC. All points of results were stable for more than 6 hours with stability range from 0.18% to 0.28%. The uncertainty was evaluated at a confidence level of 95% within 1.1% to 1.8% in the range from 10% to 92% and from 92% to 98%, respectively. The present measurement system is suitable for accurate calibration of different digital or chart hygrometers.

Design, construction and implementation of relative humidity and temperature climatic chamber for metrology laboratory

“…The second box houses the humidifier or fogger whose function is to change the water in the reservoir from a liquid to a gaseous state, generating humidity in the chamber according to the signal received from the controller [5]. To carry out the dehumidification process in the chamber, a vacuum pump was installed which removes the humid air from the chamber by passing it through a trap with a CaSO4 desiccant filter and the dry air is recirculated back into the chamber; it should be noted that the fittings and hoses through which the air circulates are totally airtight [6] [7] [8].…”