The length of hair and some synthetic fibers varies with the relative humidity of surrounding gases: the longer the relative humidity is, the longer the length is. Using this principle, a hair hygrometer can be made. When the length of synthetic fibers changes with the change of relative humidity, the position of the pointer will be changed by mechanical transmission mechanism. The hygrometer has simple structure and is widely used in meteorological measurement.
Lithium humidity meter gauge
The hygrometer has a thin layer of lithium chloride coating on its surface, which absorbs water vapor from the surrounding gas and conducts electricity. The higher the relative humidity of the surrounding gas, the higher the water absorption of lithium chloride, and the smaller the resistance between the two electrodes. Therefore, the relative humidity of the surrounding gas can be reflected by the current of the electrode. Such hygrometers are widely used in industrial processes.
Wet-dry bulb humidity meter gauge
Usually, a wet-dry bulb hygrometer consists of two glass thermometers located adjacent to each other. One of the thermometers is wrapped with a nylon mesh and the other end of the mesh is immersed in water. Due to the capillary effect, the mesh sleeve around the thermostat is always in a wet state. When water evaporates on the surface of the mesh sleeve, the heat absorption decreases the temperature of the mesh sleeve.
Thus, the temperature indicated by this thermometer (called wet-bulb thermometer) is lower than that indicated by another thermometer (called dry-bulb thermometer) without a net cover. The lower the relative humidity of the surrounding gas is, the faster the net sheath evaporates water, and the greater the temperature decrease. According to the temperature difference and the dry bulb temperature, the relative humidity of the surrounding gas can be found from the reference table attached to the instrument. The hygrometer has simple structure and is mainly used for meteorological measurement and indoor air humidity measurement.
Alumina humidity meter gauge
Its working principle is that the alumina film can absorb water from the surrounding gas and cause the change of its capacitance and resistance. The range of change is used to express the relative humidity of the surrounding gas. This kind of hygrometer is mainly used to measure the humidity of industrial process gases. It can measure the relative humidity in a wide range.