What is a hygrometer, we learn when you need to control the humidity level in a room or in the air. Such a need arises in medical institutions and museums, in libraries and in warehouses. Often you can meet the offer to buy a household hygrometer. After all, it has already been proven that the humidity in the room has a huge impact on the well-being and on the level of performance of the people in it.
To determine this indicator, which determines the degree of microclimate comfort, modern industry has launched the production of various instruments for determining air humidity.
A hygrometer is a device designed to measure the amount of moisture in the air. Its design can be based on a wide variety of operating principles. The most common hygrometers operate on the basis of a weight, hair or film sensitive element. What is an absolute hygrometer? Its other name is weight. This type of moisture measuring instrument is a construction of a U-shaped tube system. They are filled with a hygroscopic substance that is capable of absorbing moisture from the surrounding air. Having passed through the system using a pump a certain amount of air, which is tested for the amount of humidity, the mass difference is determined before and after the measurement. Having measured the volume of air passed through the system, its absolute humidity is determined .
Measurements by the weight method of determining moisture are complex, require laboratory conditions, and take a lot of time. They are rarely used, despite the high accuracy of the analysis.
A hair hygrometer works on the basis of the physical properties of non-fat human hair. Changing the length at various levels of humidity of the surrounding air, it becomes the central sensitive element of the device, which determines the relative humidity in the range of 30 - 100%. An organic film is used in the film hygrometer; it exhibits the property of stretching with increasing humidity and contracting with decreasing humidity.
It is devices with hair and membrane structures that provide an answer to the question of what a hygrometer is for winter conditions.
Both hair and film hygrometers change their properties over time. Given this fact, it is necessary to periodically compare their readings with the readings of a psychrometer, which more accurately determines the humidity of the air.
More advanced devices are electrolytic and ceramic hygrometers. In the first, the moisture level is determined by the change in the resistance of the electrolyte, which is applied by an absorbent layer of lithium chloride on the insulating plate. With all the advantages of this type of hygrometer, its readings depend on temperature. In ceramic devices, the measurement of the difference in resistance is also the basis for measuring changes in humidity. A solid porous ceramic mass is used as the sensor of this device (in composition it is a mixture of clay, kaolin, silicon and oxides of some metals).
What is a condensation hygrometer ? Let’s try to figure it out based on its design. It consists of a cooled metal mirror, a device that records the moment of dew (condensation), a thermometer that detects the temperature of the dew point, and a cooling device. A slightly altered form measures the dew point of a heated electrolytic device. This process takes place over a saturated solution of salt (usually lithium chloride).
You may notice that when using different types of hygrometers, three different quantities are measured, although they are interconnected. This is absolute, relative humidity and dew point. To move from one quantity to another, it is necessary to carry out a number of simple recalculations.