Dynamic Humidity Measurements with the Hybrid Humidity Generator

The NIST Hybrid Humidity Generator (HHG) is NIST’s primary standard humidity generator and is used for calibration of all hygrometers sent to NIST. The HHG and its accompanying temperature-controlled test chamber may also be used as a research tool for performing studies involving rapid changes in humidity. The HHG was designed to accommodate flow rates of up to 150 L/min into its test chamber of volume 40 L. This arrangement allows rapid replacement of the original air in the chamber with air from the generator that has a specified humidity, providing an environment with rapidly changing humidity. One example of studies that may be performed with this system is the measurement of the time response of a humidity sensor to changes in humidity. Another example is the measurement of moisture permeabilities of fabrics and membranes. For this second example, the measurement can be made by placing a humidity sensor in a container where one wall of the container is composed of the fabric and the other walls are impermeable to moisture.