Ancient hygrometers Edit Prototype hygrometers were devised and developed during the Western Han dynasty in Ancient China to study weather. . The Chinese used a bar of charcoal and a lump of earth: its dry weight was taken and then compared with its damp weight after being exposed in the air.
In hygrometer Dew-point hygrometers typically consist of a polished metal mirror that is cooled at a constant pressure and constant vapour content until moisture just starts to condense on it. The temperature of the metal at which condensation begins is the dew point.
Hair tension hygrometers These devices use a human or animal hair under tension. The hair is hygroscopic (tending toward retaining moisture); its length changes with humidity, and the length change may be magnified by a mechanism and indicated on a dial or scale.
Resistive Hygrometer. The conducting film of the resistive hygrometer is made by the lithium chloride and the carbon. The conducting film places between the metal electrodes. The resistance of the conducting film varies with the change in the value of humidity present in the surrounding air.
The hay thermo hygrometer PCE-HMM is a professional device to designed to determine moisture and temperature of pressed hay and straw. The hay thermo hygrometer features a sensor made of stainless steel, which can be purchased in four different lengths, while the wooden handle has an ergonomic design.