BRHU is designed to measure relative humidity in air and other gases and gas mixtures utilizing the well-known method of “dry” and “wet” thermometers with 2 identical RTD platinum sensors class ‘A’ mounted in stainless steel sheaths incorporated in a special stainless steel case, which can be installed inside or outside drying or moistening chambers. The method of “wet/dry” temperature difference provides high accuracy in RH measurement. For this accuracy to be ensured, it is absolutely necessary to keep the “wet” sensor always wet and to guarantee the evaporation from its surface. For this purpose, this probe is equipped with a special moistening system. It is also important to assure continuous gas movement along the sensors during the measurement process. Together with a BASI RH-control instrument (BTC180 or BTC390), BRHU can be widely used in areas, where capacitance RH probes are not applicable: high-temperature chambers, high-accuracy RH measurement, etc.