Application of gprscdma wireless data transmission

The application scheme of gprs/cdma wireless data transmission in heating system

the industrial application of gprs/cdma network solves the communication requirements of heating system for heating pipe control system. Compared with the traditional dedicated network, its coverage and cost are more suitable for industrial applications

I. overview

with the development of society and economy, there are more and more pipes (heat, water, electricity, oil, gas, etc.), and the collection and timely transmission of pipe measurement point data is the guarantee of stable and reliable operation of the pipe, which requires that the computer pipe monitoring system must be able to provide timely and accurate information at a low cost. However, in the process of use, the shortcomings of the traditional wired and partially wireless tube monitoring system are gradually highlighted. Using wire to transmit data cannot guarantee real-time performance; Using radio station to solve the contradiction between bit error rate and baud rate, especially anti-interference is a headache; With dedicated circuit, it is impossible to lay dedicated lines for all large-area scattered data acquisition sub stations, let alone bear high operating costs

in view of these problems, by using mature gprs/cdma wireless data transmission equipment (gprs/cdma DTU), relying on a stable and reliable gprs/cdma network, on the premise of ensuring timely and accurate data transmission, the operation cost of the on-site monitoring system is also reduced to the minimum; At the same time, the communication link is maintained by professional operators, which avoids the problem that users need to spend a lot of energy to maintain the communication line while using the monitoring system; It saves users' initial construction investment and operation and maintenance costs

II. System characteristics

gprs, CDMA wireless monitoring system has the following characteristics:

1. Good real-time response and processing ability. Compared with short message service, gprs/cdma has real-time characteristics, and the system has no time delay. The system can receive and process various data of multiple/all monitoring points in real time at the same time. The clock of monitoring points can be synchronized without round robin, which can well meet the requirements of the system for real-time data acquisition and transmission

2. Remote instrument and equipment control: due to the gprs/cdma bidirectional transmission system, the monitoring center can reverse the time correction, status report, switch and other monitoring and control functions of instruments and equipment

3. Low construction cost: the existing gprs/cdma network can be fully used, and the equipment can be connected immediately after installation. When using ultrashort wave communication, the on-site environment needs to be fully considered, and the antenna iron frame and other auxiliary equipment need to be equipped

4. Simple installation and debugging, short construction cycle: using the existing mature gprs/cdma network, the system basically does not need debugging when it is put into operation, and the installation is simple. When ultrashort wave communication is adopted, the installation and commissioning workload is large, so the on-site signal test, antenna iron frame erection, antenna direction angle commissioning and other work should be carried out first

5. Wide coverage. The construction of water supply dispatching and monitoring system requires a wide range of data communication, unlimited capacity expansion and unlimited access locations, which can meet the access needs of mountains, towns and cross regions. Due to the large number of pipe monitoring points, which are distributed throughout the city, some pipe monitoring points are located in remote areas, and the geographical location is scattered. Ultra short wave communication mode is adopted, and the coverage is only more than 30 kilometers; In theory, monitoring can be realized within the coverage of wireless gprs/cdma network by using GPRS and CDMA methods

6. High data transmission rate. GPRS network transmission rate can reach 171.2kbit/s in theory, and the data transmission rate in practical application is about 40kbps. At present, the transmission rate of general ultrashort wave data transmission stations is mostly 2.4kbit/s or lower

7. The transmission capacity of the system is large. The monitoring center station shall realize real-time connection with each pipe monitoring point. Due to the large number of monitoring points, the system is required to meet the needs of sudden data transmission, and GPRS technology can well meet the needs of sudden data transmission

8. Low communication cost, which can be charged according to time and flow

9. The system monitoring points are easy to expand and maintain

III. system composition

the system is composed of central station, communication part and monitoring station. The main station is responsible for monitoring and management. The monitoring station adopts RTU module to realize data acquisition, storage and control, and the communication part adopts gprs/cdma DTU for data communication

1. Monitoring station

the monitoring station uses RTU module to collect and process the temperature, pressure, flow, water pump current, temperature, start and stop status and other signals of the heat exchange station. RTU is connected with DTU through rs232/rs485 serial port. The collected data is transmitted by RTU to gprs/cdma DTU through serial port, and then transmitted to the central station through gprs/cdma wireless network. At the same time, it receives the command from the central station to control the water pump and regulating valve of the heat exchange station. The system can carry out real-time automatic monitoring of the heat exchange station. The operator can see the data of each heat exchange station in the main station, and control the heat exchange station to realize unattended heat exchange station

each monitoring point needs to install a monitoring box, which is required to meet the requirements of ipc55 protection level. Install one or more STC-1, stc-2 micro RTUs and a gprs/cdma DTU in the monitoring box, with 24V power supply. The box is equipped with a 220v/24vd or 12V switching power supply to supply power to RTU, gprs/cdma DTU and transmitter

◆ gprs/cdma DTU adopts CG12 or CC12 model

◆ PT100 temperature transmitter is selected as the temperature transmitter. The input is 3-wire system and the output is 2-wire system

◆ the pressure transmitter is a 2-wire device powered by 24V

◆ the flowmeter can be electromagnetic flowmeter or turbine flowmeter, and the output can be 4 ~ 20mA or frequency signal. The frequency signal can be connected to the switching input of STC-1 to calculate the flow per unit time and the total flow. The relay output of STC-1 can control the valve, which is very convenient for application

◆ for heat pump and water supply pump, stc-2 can monitor its working voltage and current, outlet temperature, outlet pressure, and flowmeter frequency signal, which can be connected to the switching value input of stc-2, and can calculate the flow per unit time, as well as the total flow. Stc-2 needs to install three current transformers

2. Wireless data communication part

wireless communication part mainly uses gprs/cdma DTU to carry out data communication between data acquisition end and monitoring center through gprs/cdma wireless network

gprs/cdma wireless data transmission (gprs/cdma DTU) is a bidirectional conversion transmission device that can immediately convert the serial port communication of industrial rs232/rs485 serial port equipment into gprs/cdma wireless network communication. The converter adopts transparent transmission mode. Users do not need to know the complex gprs/cdma communication principle and tcp/udp protocol, and can realize the wireless network connection of the original serial port equipment without changing the program, which saves you valuable time and existing investment, and can be used for long-distance communication or control. It is widely used in building automation control, parking lot equipment, traffic control, LED screen control, factory, workshop, mine, bank, electrical and other remote control fields. It can quickly realize the remote control function of serial port equipment. The transparent transmission mode of gprs/cdma wireless data transmission between two serial port devices in pairs is equivalent to extending the communication distance of the serial port, so as to realize the remote control between the serial port devices

gprs/cdma DTU features:

◆ RS232 serial port speed up to 230400 BPS

◆ support RS232 three wire standard or nine wire standard

◆ built in tcp/ip protocol stack, Support tcp/udp network protocol

◆ data terminal always

◆ drop line automatic redial function

◆ set communication parameters through HyperTerminal similar to at command mode or special setting program

◆ transparent transmission/non transparent transmission between devices

◆ support static IP or domain name connection to remote host

◆ power supply: +5v, Customized wide power, especially large wide area voltage input according to customer needs

◆ power consumption: standby state 230~330ma; Upper state 450~460ma; Transmission status 460~470ma

◆ working temperature: -30 ℃ ~ +70 ℃

◆ storage temperature: -40 ℃ ~ +85 ℃

◆ support rs232/rs485/rs422 serial port for communication

3. The monitoring center

master station adopts PC computer, which is connected to interconnection or wireless special, and the master station sends data to the slave station and receives data from the slave station. The master station receives the respective signals from the slave station and displays the output after processing. If there is an abnormal situation, it can give an audible alarm to remind the operator to take measures to prevent accidents. The system has the configuration function. According to the condition of the whole thermal system, it automatically configures each slave machine and controls the automatic operation of the whole system. The host can automatically generate various reports, and has the function of on duty inspection, regular printing and random printing, so as to realize the automatic management of the whole thermal system

the monitoring software of the monitoring center is developed with general programming tools, which has the characteristics of good flexibility and strong pertinence. It can analyze, process, save and store the collected field data and real-time data, make output reports and draw various curves, so as to realize the functions of remote meter reading, real-time monitoring and automatic management of the whole system. Friendly interface, simple and convenient operation, truly realizing high efficiency and office automation. It can be compatible with the communication protocols of multiple secondary instrument manufacturers at the same time, and can also increase the user's own communication protocol according to the user's requirements. The network database of the system makes the network management simple and easy. For the communication protocol in the transmission process, you can call the dynamic library of jizhida

IV. security measures

the data center can access to China Unicom CDMA data (VPDN). The VPDN method has relatively low cost and high security, which can fully ensure the speed and network service quality. The service provision scheme of China data (VPDN) is shown in the figure below

according to the above schematic diagram of data in China Unicom, China Unicom data can provide five levels of business security, so as to fully ensure the security of data in the network

first level security assurance: the security of CDMA network itself

at present, there are mainly two kinds of mobile communication networks used in the world: GPRS and CDMA. CDMA originated from military security technology and was widely used in the military field during the war. It has the characteristics of anti-interference, secure communication and good confidentiality. The following three methods are generally used for eavesdropping mobile signals. First, we need to capture the communication signal. The space is full of various radio waves, in which user signals are mixed. But if you want to eavesdrop on a user's call, such as plastic bags, milk bottles, clothes, etc., you must first capture the specific electromagnetic wave sent by the user. Because CDMA system adopts spread spectrum technology, the spectrum of useful signals after spread spectrum is greatly broadened, and user signals are hidden in uncorrelated signals. It is very difficult to capture this useful signal. Therefore, the eavesdropper cannot capture and recognize the communication signals of CDMA users and the noise before interest and tax profit (excluding special items) of 1.331 billion euros. Secondly, the eavesdropper must lock the signal of user communication, and then it can analyze and crack the information. CDMA adopts fast switching power control technology. Even if the eavesdropping device captures the user signal, it cannot lock the useful signal under fast power switching. Therefore, fast power switching makes it difficult to lock the CDMA signal. Third, we need to crack the user information code. While CDMA adopts pseudo-random code technology, which uses 42 bit pseudo-random code to identify and distinguish users. Every call has 4.4 trillion possible permutations, which is difficult for eavesdroppers to decipher