The definition of humidity: the less water vapor contained in a specific volume of air at a certain temperature, the drier the air; the more water vapor, the more humid the air. The degree of humidity of the air is called "humidity." In this sense, it is usually expressed by physical quantities such as absolute humidity, relative humidity, relative humidity, mixing ratio, saturation difference, and dew point; if it represents the weight of liquid water in wet steam as a percentage of the total weight of steam, it is called steam Humidity. The instrument used to measure and record humidity is called a humidity recorder. The effects of humidity on agriculture and forestry are as follows: 1. Too low humidity in misty forests can cause soil and plants to lose water and reduce production in agriculture. 2. Humidity is also a very critical quantity in the forestry and forestry industry. At the sawmill, people often water the wood stacked there. The wood itself has its humidity, and its humidity in the air gradually approaches the humidity of the surrounding air. Changes in the humidity in the wood will cause changes in the wood volume, which is critical for the forest industry. 3. Generally, when storing wood, the air should be in direct contact with it in all directions to prevent the wood from being deformed or moldy. When laying the floor, it is best to let the wood stand for a day or two to make it the same as the humidity in the house. Otherwise, the wood on the floor may stretch or shrink after laying.
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Humidity measurement technology has a long history. With the development of electronic technology, modern measurement technology has also developed rapidly. Humidity measurement is divided into as many as 20 to 30 in principle. The expression methods of humidity include absolute humidity, relative humidity, dew point, the ratio of moisture to dry gas (weight or volume), etc. But humidity measurement has always been one of the famous problems in the world of metrology. A seemingly simple value, when studied in-depth, involves quite complex physics-chemical theoretical analysis and calculations. The beginner may ignore many factors that must be paid attention to in humidity measurement, thus affecting its reasonable use. Standard humidity measurement methods are: · Dynamic method (double pressure method, double temperature method, shunt method). · Static method (saturated salt method, sulfuric acid method). · Dew point method. · Dry and wet bulb method and various electronic sensor methods. Double pressure method and double temperature method: It is based on the principle of thermodynamics P, V, T balance, the balance time is longer, and the split method is based on the precise mixing of absolute moisture and final dry air. Due to the modern measurement and control methods, this equipment can be made quite precise. Still, because the equipment is complex, expensive, and time-consuming and labor-intensive, it is mainly used for standard measurement, and its measurement accuracy can reach ±2%RH-±1.5%RH. The saturated salt method in static method: It is the most common method in humidity measurement, simple and easy to implement. However, the saturated salt method has strict requirements on the balance of liquid and gas phases and higher requirements on ambient temperature stability. To use it requires a long time to balance, and the low humidity point requires a longer time. Especially when the difference between the indoor humidity and the humidity in the bottle is significant, it needs to be balanced for 6 to 8 hours each time it is turned on. The Dew point method measures the temperature when the humid air reaches saturation, which is a direct result of thermodynamics, with high accuracy and a wide measurement range. The accuracy of the precision dew point meter used for measurement can reach ±0.2℃ or even higher. However, the cold mirror dew point meter using the modern photo-electric principle is expensive, and it is often used in conjunction with a standard humidity generator. Wet and dry bulb method: It is a method of measuring humidity invented in the 18th century. It has a long history and is the most commonly used. The wet and dry bulb method is indirect. It uses the wet and dry bulb equation to convert the humidity value, and this equation is conditional: the wind speed near the wet-bulb must reach 2.5m/s or more. The standard dry and wet bulb thermometer simplifies this condition, so its accuracy is the only 5~7%RH, which is significantly lower than that of the electronic humidity sensor. The wet and dry bulb does not belong to the static method. Don't simply think that as long as the measurement accuracy of the two thermometers is improved, the measurement accuracy of the hygrometer is improved. Regarding the Measurement Method, Two Points are Emphasized: First, because humidity is a function of temperature, temperature changes decisively affect the measurement results of humidity. Regardless of the method, accurately measuring and controlling the temperature is the priority. Note that even if it is a well-insulated constant temperature and humidity box, the temperature in the working room also has a specific gradient. Therefore, the humidity in this space is also brutal to be completely uniform. Second, due to the significant differences in principles and methods, it is difficult to calibrate and confirm various measurement methods directly. Most of them can only be compared by indirect methods. Therefore, it is tough to calibrate the measurement results of the whole humidity range (relative humidity 0~99.9%RH) between the two humidity measurement methods or to calibrate the measurement results of each point in all temperature ranges. For example, the ventilated wet and dry bulb hygrometer requires flowing air with a specified wind speed, while the saturated salt law requires strict sealing, and the two cannot be compared. The best way is to confirm it step by step according to the transmission method and verification procedures stipulated by the country for the verification system (standard) of humidity measurement instruments.
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In winter, the temperature is 18 to 25°C, and the humidity is 30% to 80%; In summer, the temperature is 23 to 28°C, and the humidity is 30% to 60%; People who feel comfortable in this range account for more than 95%. In an air-conditioned room, people will feel most comfortable when the room temperature is 19 to 24°C, and the humidity is 40% to 50%. If you consider the influence of temperature and humidity on people’s thinking activities, The most suitable room temperature should be 18℃, The humidity is 40% to 60%, At this time, people are in a good state of mind, and their thinking is the quickest.
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The dew point transmitter measures not only the humidity in the gas but also the temperature. Dew point transmitter refers to the temperature when the air is cooled to saturation under the condition that the water vapor content and air pressure do not change. To put it vividly, the temperature when the water vapor in the air turns into dew is called the dew point temperature. Dew point temperature is a temperature value, but why use it to express humidity? When the water vapor in the air is saturated, the temperature is the same as the dew point; when the water vapor is not saturated, the temperature must be higher than the dew point temperature. Therefore, the difference between the dew point and the temperature can indicate the degree of saturation of the water vapor in the air. At 100% relative humidity, the temperature of the surrounding environment is the dew point temperature. The lower the dew point is than the temperature of the surrounding environment, the lower the possibility of condensation, which means that the drier the air, the dew point is not affected by temperature but is affected by pressure, and the application is generally in container ships. If the outside air temperature is lower than the internal temperature of a closed space such as a cabin or a container, moisture is formed on the metal surface inside the ship or container. On the other hand, if the temperature of the outside air is higher than the temperature inside the ship or container, moisture is directly formed on the surface of the cargo. In some cases, it is necessary to ventilate the cabin to change the dew point temperature to avoid condensation. At this time, the dew point sensor needs to be installed.
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Over the past few decades, the sensor industry has undergone earth-shaking changes. Advances in technology and the Internet of Things have led to more diverse ways of transmitting data. Various types of sensors can not only monitor data in real-time but also based on corresponding usage scenarios. Choose different data transmission methods to upload to the cloud platform to access it whenever we need it. Let's take the temperature and humidity sensor as an example to talk about the four data transmission methods of the sensor. Let me first state that these four data transmission methods are not limited to temperature and humidity sensors. Because the temperature and humidity sensor is standard in our daily life, the data uploading method is more comprehensive and relatively representative. The temperature and humidity sensor has four types of data upload: 485 types, analog type, network type, and wireless type. 1.Type 485 Type 485 data transmission is called RS-485 in full. RS-485 is developed based on RS-422, so some electrical regulations are similar to RS-422. For example, all adopt balanced transmission mode, and all need to connect terminal resistors on the transmission line. And 485 can choose the two-wire or four-wire mode, and the two-wire system can realize accurate multi-point two-way communication. When the four-wire system is adopted, only point-to-many communication can be realized. However, 32 devices can be connected to either the two-wire system or the four-wire system bus. When the applicable range of RS-485 is from tens of meters to thousands of meters, the RS-485 serial bus standard is adopted. Please connect to the environmental monitoring host through the RS-485 interface, upload it to the cloud platform from the environmental monitoring host, or directly connect to the computer through USB to 485 to achieve real-time data display, historical data query, data export and other functions. AW5485 Temperature and Humidity Transmitter For example, Losing Electronics introduced the RS485 interface temperature and humidity transmitter-AW5485, which has a beautiful and small appearance, a standard guide rail structure design, simple wiring and easy installation. Super stability and anti-interference ability, strong product protection performance, first-class lightning protection. RS485 interface, multiple modules connected to the bus network together, real-time monitoring of multiple on-site environments. It is widely used in industrial plants, telecommunications base stations, communication rooms, HAVC HVAC, intelligent buildings, workshops, warehouses, pharmacies, libraries, museums, laboratories, offices, ventilation ducts, greenhouses and other places. It is a variety of applications The ideal solution for environmental temperature and humidity measurement and monitoring. 2. Analog type Focus on the analog data transmission method. In the control system, whether input or output, a parameter is either an analog quantity or a switch quantity. The analog temperature and humidity sensor use analog data transmission. The analog sensor sends out a continuous signal, using voltage, current, and resistance to indicate the size of the measured parameter. Taking the analog temperature and humidity sensor as an example, there are several output signals: 0-20mA, 0-5V, and 0-10V. Take the 0-20mA output signal conversion calculation: for example, the range is -40~+80℃, 4~20mA output, when the output signal is 12mA, calculate the current temperature value. The span of this temperature range is 120°C, when expressed by a 16mA current signal, 120°C/16mA=7.5°C/mA, that is, 1mA represents a temperature change of 7.5°C, and the measured value is 12mA-4mA=8mA, 8mA*7.5°C/mA= 60°C. 60+(-40)=20℃, the current temperature is 20℃. The other two can be deduced by analogy. Analog Output Type Temperature and Humidity Sensor-AM1011A For example, the temperature and humidity sensor-AM1011A output by Aosong electronic analog model is a temperature and humidity sensor with calibrated analog signal output, the sensor signal adopts analog voltage output mode; this module has high precision, high reliability and good consistency, And with temperature compensation, to ensure long-term stability, easy to use and high-cost performance, especially suitable for enterprises with stricter quality and cost requirements. Applications include HVAC, dehumidifiers, testing and inspection equipment, consumer products, automobiles, automatic control, data loggers, weather stations, home appliances, humidity control, medical and other related temperature and humidity detection and control. 3. Network Type ①Ethernet Ethernet is currently the most commonly used LAN technology, replacing other LAN technologies such as token ring, FDDI and ARCNET. The Ethernet type transmission method can upload the collected data to the server through the Ethernet method. Make full use of the established Ethernet communication network to realize data collection and transmission and achieve centralized monitoring. It can significantly reduce the amount of construction, improve construction efficiency and maintenance costs. ②WIFI type The WIFI type wireless data transmission method can upload the collected data to the server through the WIFI method. Make full use of the established WIFI communication network to realize data collection and transmission and achieve centralized monitoring. It can significantly reduce the amount of construction, improve construction efficiency and maintenance costs. WIFI Type Temperature and Humidity Transmitter-AW5145W For example, Losing Electronics’ WIFI temperature and humidity transmitter-AW5145W, which is a network transmitter that uses a digital temperature and humidity sensor, converts the temperature and humidity in the environment into corresponding digital signals; WIFI or wired network connection, upload the temperature and humidity data to the host for real-time monitoring; the sensor uses a high-quality integrated digital temperature and humidity sensor to ensure the transmitter’s excellent long-term stability, low latency, and resistance to chemical pollution. Excellent repeatability. Applications: Meteorology, scientific research, post and telecommunications, tobacco, chemical industry, environmental protection, archives and cultural relics preservation, medical and health, hotels, food and other related temperature and humidity monitoring and control. ③GPRS type GPRS is the abbreviation of General Packet Radio Service Technology. It is a mobile data service available to GSM mobile phone users and belongs to the data transmission technology in the second generation of mobile communications. Based on GPRS transmission, the temperature and humidity transmitter only needs a SIM card of China Mobile, China Unicom or Telecom to upload the collected temperature and humidity data to the server through the network base station. 4. Radio Type Radio refers to electromagnetic waves that propagate in free space (including air and vacuum), and radio technology is a technology that transmits signals through radio waves. The radio-type sensor adopts wireless spread spectrum technology. The communication distance is long, the line of sight can reach 800 meters, the penetrating ability is strong, and it can penetrate 3 to 4 concrete walls. Due to the frequency modulation technology, the communication is compared with standard radio equipment. Strong anti-interference ability. The wireless intelligent temperature and humidity recorder launched by Aosong Electronics
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