Hygrometer with LED display and switched output

The measurement and control of the moisture content of gases, such as the atmosphere around us, is an integral part of many industries, but is also of importance in the home and workshop. Although moisture, that is, water vapour, is not an ideal gas, for many hygrometry purposes it is sufficient to assume that it behaves ideally. In environmental applications the basic unit of moisture is relative humidity, which is the ratio in per cent of the actual vapour pressure in the atmosphere to the saturation vapour pressure of water at the same temperature. It is thus temperature dependent but independent of the atmospheric pressure.