Composition of soil moisture automatic monitoring system
The public opinion monitoring automation system is an advanced automatic system for collecting and processing soil moisture parameters. It applies high-precision sensing technology, communication technology, database storage and processing technology, and realizes the automatic collection, transmission and storage of soil moisture data under no-arrest conditions, providing a basis for statistics, analysis and prediction of soil moisture changes. The system can be widely used in fields such as water conservancy, early agriculture, precision agriculture and urban afforestation.
In China, soil moisture monitoring began in the middle of the last century. Drying weighing, neutron moisture measurement, and TDR time-domain reflectometry were used. Although these methods can measure soil moisture, they cannot The automatic work in the field and in the absence of people will not be able to realize the automatic transmission, processing and statistics of public opinion data, and it will not be able to adapt to the current needs of agriculture, early decision-making, and the modernization of urban greening. For this reason, it is necessary to build a public opinion monitoring automation system.
1 System composition and function The real-time soil moisture monitoring system is a complete solution from the collection, transmission and storage of soil moisture data to the centralized management, statistical analysis, prediction and display of a large number of collected data.
From the structure points: It consists of three parts: monitoring center, data transmission channel, and acquisition terminal, as shown in Figure 1.
Functionally, the system can be further divided into:
(l) Basic data subsystem: Extract basic information about population and arable land, crop yield, irrigation area and early-to-early facilities from the database and display the printouts by means of chart curves;
(2) Information acquisition and storage subsystem: Collect soil moisture data of all public opinion stations in real time, and store the database in a unified format after rationality discrimination, data processing, and protocol conversion;
(3) Retrieval subsystem: In addition to the available maps, tables, or printable real-time public opinion information, characteristic values, forecast results, and system anomaly replacement information for each reservoir, it is also possible to browse historical data and historical forecast results. Search, query, modify, backup, restore, etc. on the database;
(4) Real-time early-warning forecast subsystem: built-in expert forecast model. Using the organic combination of monitoring real-time data and related theories, the multi-model and multi-parameter analysis and calculation are performed to obtain scientifically-based forecast results for decision-making by the leaders and the anti-earlys headquarters;
(5) Communication Subsystem: The use of wireless CSM, VHF, satellite and wired PSTN communications, construction of the system's network communications, realize the transmission of public opinion data.
2 System Design 2.1 Public Monitoring Station of Public Opinion Monitoring Center The monitoring central station of the public opinion monitoring system adopts a workstation work duty system to complete the data collection, processing, alarming, storage, display, printing, and through telephone lines, satellites, etc. of all telemetry stations in the system. The channel reports data to the upper-level department; it can remotely detect the running status of the collection terminal, query and set various parameters, and call and measure the soil moisture content of the collection terminal; for the public opinion calculation, early-morning warning, anti-early schedule and decision-making services . The equipment consists of: receiving decoding equipment (according to the communication channel selection cSM, VHF, satellite and PSTN), public opinion workstation (computer) and anti-jamming power supply configuration.
The main function:
(1) Public sentiment data query: In the window, the query time, test station station number, and city are selected, and the system obtains the data of the public opinion test stations from the server database;
(2) Distribution map of public opinion: The values ​​of the public opinion marked in each figure are shown in the figure, and are represented in different colors according to the size of the value;
(3) Early-morning analysis: According to factors such as soil moisture content, pre-rainfall, pre-irrigation, soil distribution, crop distribution, crop growth period and other factors, early-morning surface distribution maps were formed, and different types of data were statistically analyzed by spatial superposition analysis. Early area
(4) Early intelligence table: In the time of selecting the query in the window, the system will obtain the statistics of early-morning activity and project statistics and anti-early activity statistics from the server database.
2.2 Remote Sensing Telemetry Station Remote Sensing Telemetry Station is an automatic telemetering station for field work, unattended, and automatic collection of public opinion data (divided into two types: mobile station and fixed station). It mainly realizes the automatic collection and storage of soil moisture data, and submits data and receives instructions to the system monitoring center through communication networks (CSM, VHF, satellites, and PSTN MODEM). It can automatically work in the field environment, real-time collection of public opinion data, according to set requirements for regular transmission, the station can also be configured rain t, temperature, evaporation, wind speed / direction, air pressure and other sensors constitute an unmanned weather station. Equipment configuration includes: sensor, remote sensing terminal, power supply system (using solar floating charge, battery power configuration), communication equipment (csM, vHF, satellite and Ningm NMODEM), antenna feeder and so on. The composition of the telemetry station is shown in Figure 2.
Figure 2 Block diagram of public opinion telemetry station
The remote sensing station adopts a gap-type continuous operation mode to continuously record and record the maximum public opinion data in real time, and automatically submits the report according to the preset self-reporting time (it can also work in the call-receiving/response system). The reporting timing can be set to : 6h, sh, 24h.
The telemetry station can use four kinds of operation methods such as call-in survey, patrol test, self-report, and manual transmission.
(1) Calling test: The monitoring center sends instructions to the public opinion monitoring station. After the public opinion monitoring station receives the instruction, it collects real-time soil moisture content data, and sends the data preparation to the monitoring center.
(2) Inspection: The monitoring center sends instructions one by one to the public opinion monitoring station. The public opinion monitoring station receives real-time soil moisture data after receiving the instruction, and sends the data preparation to the monitoring center one by one.
(3) Self-reporting: The public opinion monitoring station collects real-time soil moisture content data at set intervals and sends the data preparation to the monitoring center.
(4) Manual sending: Through terminal terminal operation, the terminal collects soil moisture data in real time and sends the data to the monitoring center.
2.2.1 Public opinion telemetry terminal The public opinion telemetry terminal is the terminal acquisition equipment of the public opinion monitoring system (divided into two types: mobile station and fixed station). It is mainly used for automatic collection and storage of soil moisture data and passes GSM, VHF, satellite or PsTNMoDEM communication equipment and system monitoring center for instruction and data exchange. The terminal is a new type of telemetry terminal developed on the basis of a mature telemetry data terminal. It has greatly improved functions, interface design, and reliability design. The new design uses advanced microprocessor technology and huge software support. The terminal consists of a control board and a communication interface.
The main functions are as follows:
(1) Directly connect with soil moisture sensor (soil moisture sensor) to measure soil moisture content in real-time, on-line, and automatically; at the same time, it can also connect with rain gauge, thermometer, barometer, wind/wind direction sensor and various telemetering water level gauges. Constitutes an unmanned automatic weather station;
(2) Interfaces with communication equipment such as GSM mobile phone short messages, VHF ultra-shortwave, satellite and PSTN. According to the on-site communication conditions, select the communication channel design;
(3) Various parameters can be set, such as station number, sampling interval time, self-reporting time, parameters of the channel machine, etc.;
(4) Random self-reporting, timing self-reporting and answering functions;
(5) When using the programmer, it has an artificial set function;
(6) It has a solid-state storage function, and it can save data and device information when power is off;
(7) Low power consumption and power supply voltage alarm function.
2.2.2 Public opinion sensor The MP-406 public opinion sensor is a soil moisture sensor adopting world advanced technology, which is precise, reliable and durable. The performance can be comparable to the foreign time domain reflectometer TDR and neutron moisture meter NeutronProbe, cheap, no radioactive sources. The MP-406 consists of a shaped probe containing a watertight chamber containing electronics and four stainless steel needles connected to one end. The probe is inserted directly into the soil to generate high frequency signals and measure soil parameters. When inserting soil, the impedance of the probe (transmission line) varies with the impedance of the soil. The impedance of the probe includes the dielectric constant of the soil and the ion conductivity; the frequency of the electrical signal selected by the sensor minimizes the influence of ion conductivity. The impedance change of the probe (transmission line) is almost only dependent on the change of the dielectric constant of the soil. These changes produce a voltage standing wave. The standing wave changes with the medium around the probe. The internal oscillator of the sensor generates the voltage, which is generated by the oscillator. The difference between the voltage and the probe return voltage measures the dielectric constant of the soil; the cable at the end of the probe connects the power supply and outputs an analog signal, measuring this analog signal, and measuring the soil moisture content.
The main technical parameters of MP-406 type lyrical sensor:
(1) Measurement parameters: Soil volumetric water content (m3/m3 or %vol.);
(2) Range: 0 to 1.0m3/m3;
(3) Accuracy: ±0.02m3/m3 after specific soil calibration, or ±0.05m3/m3, using a given soil calibration. For all common soils, soil moisture is 0.05-0.6m3/m3, ambient temperature is 0- 40 °C, can use the data collector;
(4) Soil conductivity range: Accurate data can be obtained for soil conductance in the range of 0 to 0.15/ml;
(5) Soil sampling volume: 90% of the influence is in a cylinder with a diameter of 2.5 cm and a length of 6 cm surrounding the central probe;
(6) Environment: Long-term burial in different soils or water without affecting function and corrosion;
(7) Settling time: power about 105;
(8) Response time: Response to 99% of changes within 0.55;
(9) Task cycle: 100% (can be continuous operation);
(10) Working conditions: power supply: 7-15VDC non-stable voltage; power consumption: 19mA (conventional), maximum 21mA; output signal: (0-0.5m, / soil moisture-resistant to about 0-IVDC):
(11) tube sealing material: PVC;
(12) Probe material: Stainless steel;
(13) Cable length: standard: sm, longest: 1O0m.
Statistical data show that there is a linear relationship between the square root of the dielectric constant of the soil and the volumetric water content of the soil, and this relationship is suitable for a variety of soils. The output voltage in O-IVDC indicates that the soil dielectric constant is between 1-32. This range represents the volumetric water content of general mineral soils of 0.5m3/m3.
3 Installation and commissioning (1) Selection of measuring points should try to avoid holes, stones, and roots;
(2) Insert soil moisture (moisture) sensor: The sensor is buried in the measuring point according to different buried depth parameters, and the sensor probe must be completely inserted into the soil and compacted;
(3) Installation of remote sensing station: Connect the soil moisture sensor and GSM signal antenna (or VHF antenna, satellite antenna, and PSTN telephone line) separately;
(4) Debugging acquisition terminal station: After the power of the telemetry terminal is connected, the telemetry terminal will first “self-test†when it is powered on; if the real-time sampling result is displayed, it means “self-test†passes; after the manual data transmission is completed, the installation and debugging are completed.
4 Application of key technologies (1) Application of high-frequency standing wave measurement technology The MP-406 soil moisture sensor is a soil moisture sensor that uses high-frequency standing wave measurement technology to indirectly measure the dielectric constant of soil. The sensor realizes “time domain reflectionâ€. "TDR" and "NeutronProbe NeutronProbe" are difficult to implement online, automatic, safe, low-cost and other requirements, the application of the sensor technology makes remote sensing possible.
(2) Application of GSM Communication Technology Public opinion monitoring stations are generally one township, and even one county only has one, with a wide area and few stations. Data acquisition system communication methods currently include ultra-shortwave, satellite, telephone, GSM and other. Ultra-short wave communications have matured technologies and products in the establishment of water level telemetering systems. However, ultra-short wave communications require the establishment of dedicated communications networks, limited transmission distances, and the need to build relay stations. This is not appropriate for flood monitoring systems with a wide area and few stations. The appearance of cable and satellite has the characteristics of being free from distance restrictions and the need to set up a dedicated communications network, but the investment is relatively high; and GsM communication has the advantages of simple equipment, easy installation, unrestricted transmission distance, low operating cost, and low cost of civil construction and investment. Such characteristics, which provide guarantee for the promotion and application of public opinion monitoring automation system construction.
5 System characteristics (1) The soil moisture monitoring terminal is easy to use, efficient and time-saving, and its promotion will replace the traditional data acquisition methods and save a lot of manpower and material resources and time;
(2) Provide three unique operating modes and three operating modes, which may meet the needs of different applications.
(3) The public network such as GSM wireless communication and PSTN telephone can be used as the data transmission channel, which can reduce the construction and operating costs of the acquisition system;
(4) Data processing and transmission are fully automated, and data distortion due to human factors is avoided in the transmission process;
6. Conclusion The system has successfully realized the automatic monitoring of soil moisture, which can be widely used in greenhouses, flowers, vegetables, pastures, water-saving agriculture and other precision agriculture. It can provide real-time soil moisture data online, thus improving flood prevention decision-making system. Forecast accuracy and early decision-making basis.
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