The principle of operation of hygrometer is to analyze the effect of variations in humidity on a certain type of body and matter. For example, hair hygrometers based on the ability of skimmed human hair to change its length in response to changes in humidity. Such hygrometers measure the humidity in the range 30-100%. In film hygrometers moisture sensitive element is an organic film.
Although film and hair hygrometers are not able to give such accurate measurements, which is given by the psychrometer. But in winter, the main means of measuring the relative humidity of the air are all the same hygrometers, which are also the weight, the electrolytic condenser and ceramic. Each of these types of hygrometers has its own characteristics. But the base one for all: the hygrometric method of measurement or determination of the dew point.
Psychrometric method of measuring relative humidity is also very popular. The hygrometers accuracy can reach 5%, but psychrometers much more accurate. Standard the simplest psychrometer consists of two thermometers. One dry and the second wet. The second is wrapped in water soaked cotton cloth. Evaporating water cools the thermometer, and at this time the second (dry) thermometer shows the temperature of the surrounding air. Testimony in the end are transmitted to the evaluation unit, which determines the relative humidity of the indoor air based on the difference in temperature between the dry and wet thermometers.
If neither psychrometer or hygrometer you do not, humidity can be measured without them. Type in a glass of cold tap water and place it in the fridge for a couple of hours. Make sure that the water temperature has not dropped below $ 5. Put a stack in the room so she was away from heaters. Now watch the pile for several minutes.
If the walls of the stack began to fog up and they're dry in five minutes, so the humidity is very low, that is, the air is dry;
On average humidity is "misleading" wall of the stack, and the remaining fogged;
If the surface of the glass within five minutes of the formation of small streams of water, so the humidity in the room high.