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The sensor is an important part of the detection link of the temperature and humidity monitoring system in the greenhouse. The sensor in the greenhouse is used to convert non-electrical physical quantities such as greenhouse environmental factors into electrical signals that can be recognized by the control system, and provide a basis for judgment and processing for system management control. The main technical indicators of the sensor are: linearity, sensitivity, hysteresis, repeatability, resolution, drift, accuracy, etc. Commonly used sensors include temperature and humidity sensors , light sensors , CO2 (carbon dioxide) sensors, soil temperature and humidity sensors, and salt (EC) and acidity (PH) sensors for nutrient solutions.
(1) Air temperature and humidity sensor
The suitable growth temperature for most crops is between 12 ° C and 33 ° C. The temperature measurement range in a greenhouse is generally 0 ° C to 80 ° C, and the humidity measurement range is 0% to 100% RH. The power supply voltage is based on the industrial standard 24VDC. The output signal is (4 to 20) mA, and the accuracy is temperature ± 0.5 ° C and humidity ± 3% RH. The output signal is very linear and can be transmitted over long distances.
Temperature and humidity sensors are mainly divided into indoor and outdoor temperature and humidity collection units. Outdoors generally use light louvered temperature and humidity to prevent solar radiation and rain. The temperature and humidity sensors with and without display are generally used indoors. Regardless of the type of sensor, their role is to collect the indoor and outdoor temperature and humidity parameters in real time and send them to the control cabinet through the data line to complete the front-end data collection function. According to the data sent back by the sensor, the system uses comparative calculations and logical judgments to determine the equipment whose control output has a decisive effect on the thermometer, which is used to adjust the indoor temperature and humidity parameters.
(2) Selection of illumination sensor
Light is the main energy source for photosynthesis of plants. It is related to light intensity and light time. It uses a high-sensitivity silicon blue photovoltaic detector as a sensor, which has a wide measurement range, convenient use, easy installation, and long transmission distance. The power supply voltage is 24VDC, the accuracy is ± 7%, the measurement range is 0 ～ 200KLux, the output signal is (4 ～ 20) mA, the operating environment temperature is 0 ～ 70 ℃, and the humidity is 0 ～ 70% RH. The light sensor is mainly used in the outdoor environment. The outdoor sunlight is detected and sent to the controller. The controller determines whether to use the shade net of the greenhouse through internal calculations and logical judgments.
(3) CO2 sensor
For carbon dioxide transmitters with high standards, the sensor uses a silicon-based non-scattering infrared sensor with a unique built-in reference; advanced single-beam dual-wavelength measurement, no moving parts, and excellent long-term stability. The sensor monitors the indoor CO2 concentration in real time, and adjusts the supplement of CO2 gas to ensure the required concentration of carbon dioxide under photosynthesis of indoor plants.
(4) Soil temperature and humidity sensor
Plants mainly rely on the water absorbed by the roots from the soil to provide physiological activities and transpiration, such as plant growth and metabolism. More than 90% of the water required by plants for photosynthesis and transpiration comes from the absorption of water in the soil, and the amount of water absorbed by the roots is closely related to the soil temperature, so during the planting process, soil temperature and soil humidity (water) are crop growth An important factor. The selection range of soil temperature and humidity sensor is generally between -20 ℃ ~ + 85 ℃, humidity 0 ~ 100% RH, working condition temperature -15 ℃ ~ 60 ℃, humidity 10% RH ~ 80% RH. For wireless transmission, you can choose to transmit soil temperature and humidity sensors over long distances.
(5) Soil salinity detector
Soil salinity is an important indicator for the healthy growth of crops. Excessive soil salinity can lead to physiological drought in plants. Due to the toxic effects of ions in the soil, the normal metabolism of plants will be destroyed, leading to the destruction or death of plants. For the selection of soil salinity sensors, it is necessary to pay attention to the range of salt: 0.01mol / L ~ 0.3mol / L, conductance: 0mS ~ 20mS; working conditions: select temperature -10 ℃ ~ 60 ℃, humidity 10% RH ~ 90% RH.
(6) Soil pH detector
Soil pH is an important indicator of plant survival. Plant growth will be greatly affected if soil pH is unsuitable. Soil pH sensor (soil conductivity sensor) is a new generation of conductivity soil pH sensor with world advanced level independently developed by our company based on conductivity theory and using frequency domain measurement technology. It can measure the conductivity characteristics of soil (or other media) and other (fine) porous media, and convert it into a linearized standard voltage signal output, which can be used for real-time monitoring of soil / media conductivity. At present, this product has been widely used in agricultural irrigation, agricultural soil pH research, sand soil planting, and on-line measurement of soil conductivity for concrete mixing. The range of soil pH sensor is generally selected from 3PH ~ 8PH.
The agricultural greenhouse greenhouse environment remote monitoring system consists of temperature and humidity sensors, light sensors, C02 concentration detectors, leaf surface humidity sensors, etc. to complete the monitoring, summary, conversion and transmission of environmental parameters. Combined with the control part, the greenhouse can be completed. Environmental monitoring.
November 11, 2016
Chengdu Xinxin Electronic Technology Co., Ltd. Editorial Department
Editor: Little Devil in Gourd