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Working principle of temperature and humidity transmitter for concrete curing

by:Rika Sensors     2021-11-13
Working principle of temperature and humidity transmitter for concrete curing
The performance of concrete is mainly manifested in the physical and mechanical properties and durability, and the physical and mechanical properties are mainly the strength of concrete. The strength of concrete is a gradual development process. The degree and speed of its development depends on the hydration status of the cement. Temperature and humidity are important factors that affect the speed and degree of cement hydration. Therefore, after the concrete is formed, it must be maintained at an appropriate temperature and sufficient humidity for a certain period of time to make the cement fully hydrated. This is the curing of the concrete.

my country's national standard GB/T50081-2019 'Standard for Test Methods of Concrete Physical and Mechanical Properties' stipulates that the temperature of the standard curing room is 20±2℃ and the humidity is above 95%. Because the environment required for the concrete curing room requires high temperature and humidity, special temperature and humidity monitoring equipment is generally used to monitor the temperature and humidity of the curing room to facilitate understanding of the environment of the curing room and ensure that the temperature and humidity in the curing room meet the national standard.

There are two main types of modern humidity measurement solutions: the wet and dry bulb method and the electronic humidity sensor method.

The maintenance of the wet and dry bulb method is quite simple. In actual use, you only need to add water to the wet bulb or replace the wet bulb gauze regularly to keep the wet bulb humidity. Compared with the electronic humidity sensor, the wet and dry bulb method will not cause problems such as aging and decreased accuracy. Therefore, the wet and dry bulb method is more suitable for use in high temperature and harsh environments.

Because the required humidity of the concrete curing room is above 95%, the humidity is relatively high, so the temperature and humidity transmitter for the concrete curing room generally adopts the principle of dry and wet bulb, and the temperature and humidity transmitter of the principle of dry and wet bulb consists of two Thermometers with exactly the same specifications, one is called a dry bulb thermometer, whose temperature bubble is exposed to the air to measure the ambient temperature; the other is called a wet bulb thermometer, whose temperature bubble is wrapped in special gauze and keeps the gauze When wet, the moisture in the gauze continuously evaporates to the surrounding air and takes away heat, so that the temperature of the wet bulb drops.

The moisture evaporation rate is related to the moisture content of the surrounding air. The lower the air humidity, the faster the moisture evaporation rate, which leads to the lower the wet bulb temperature. It can be seen that there is a certain functional relationship between the air humidity and the temperature difference between the dry and wet bulbs. The wet and dry bulb hygrometer uses this phenomenon to determine the air humidity by measuring the dry bulb temperature and the wet bulb temperature.

If the amount of water vapor in the air is not saturated, the surface of the wet bulb will continuously evaporate water vapor and absorb the heat of vaporization, so the temperature indicated by the wet bulb is lower than that indicated by the dry bulb. The drier the air (that is, the lower the humidity), the faster it evaporates, and it continuously absorbs the heat of vaporization, so that the temperature shown by the wet bulb decreases, and the difference between the wet bulb and the dry bulb increases. On the contrary, when the amount of water vapor in the air is saturated, the water will no longer evaporate, nor will it absorb the heat of vaporization, and the temperature shown by the wet bulb and the dry bulb will be equal.

When using, the temperature and humidity transmitter should be placed at a height of 1.2 to 1.5 meters from the ground. Read the temperature difference indicated by the dry and wet balls, and the relative humidity of the air at that time can be found from the comparison table attached to the hygrometer.

Because the moisture of the gauze wrapped by the wet bulb evaporates not only with the relative humidity of the air at that time, but also with the air circulation speed. Therefore, the comparison table attached to the dry and wet bulb thermometer is only applicable to the specified wind speed, and cannot be used arbitrarily.

The indication of the wet bulb temperature gauge is usually lower than the dry bulb temperature. According to the indications of the dry-bulb and wet-bulb temperature tables, the absolute humidity, relative humidity, saturation difference, and dew point temperature of the air during the observation can be checked using the humidity look-up table.



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