The Remote Monitoring And Control System Which Is Based On The Public Telephone Network To Urban Heating Network

Nowadays, data communicational technology is applied more and more extensively in Industry field. Many control systems require doing the remote monitoring and centralized management to the equipments which are scattered at the scene or the urban areas. It can be more widely used in different trades, such as supplying of heat, gas, petrochemical and bank etc. The telephone network is widely coverage in the application of these industries at the scene. Therefore telephone network has its advantages which are used very convenient and the widely coverage of resources in the communication network.In this paper, it researches a remote monitoring system to use public telephone network as a transmission medium. The System uses a PC machine as the upper computer to monitor the host, the single chip as the lower computer to collect data acquisition unit, and the use of telephone lines as a data exchange and transmission between the two media, the use of Visual Basic as a platform to monitor and manage software to realize the data monitor and emergency treatment in the scope of urban area. Because of the stability of telephone network communication lines, small interference, wide coverage area and no personal management, this system has a great application prospect.Recently, the public telephone network remote-controlled technology universally through modems designated manipulate tel-dual audio decoder, driver charged equipment. Modem is based on the use of the DTMF signals to a remote control of communications between the terminals. DTMF is a programming technology that uses two specific single audio signals to represent the digital signal in order to achieve its function. Two different single audio signals with different frequencies, on behalf of its figure or its function are different. Generally, using with eight different types of single audio signal, we can apply eight kind of frequency, so called it multi-frequency. And because it chooses two from eight frequencies arbitrarily to combine and code, so we also known it as the "take 2 of 8" of the coding techniques. Applying this technology, a remote telephone terminal can identify whether there is any phone call to the signal, if have the signal, it will connect the phone and set up communications.Like other communication standards, MODEM communication also has its own rules and standards. AT command set up allows the DTE release from the complex mission mentioned above, and ring detection, carrier detection, the rate choice can be finished through setting up MODEM to achieve. At the same time, TXD and RXD not only transmit data, but also to send AT commands. DTE send a command to the MODEM, MODEM implement it and through RXD to give the results to DTE. MODEM by AT command and the situation of some specific registers to determine DTE issued a command or data. Correspondingly, MODEM status can also be divided into the command status and online status. Except the limited time used Dial-up, MODEM always is in the online status. When Modem launched, the first state is in the command status, then linking into the online status. MODEM status which under the AT command to receive an order form. Online at the next status, MODEM communicates with the remote system. MODEM no longer attempts to interpret the data which send to it, but rather send it directly.The key point to build up public telephone network is the design of the interface circuit. This design is the use of modem Si2457 and Si3008 line to control the circuit combine with the interface circuit of the public telephone networks. Computer or single-chip computer to control the initialization of the MODEM chip and make the remote control terminals hanging up the picking machine come true. Si3008 Line control circuit can transfer the signals set up by Modem chips into the signals which the phone line transmit.When the telephone lines connect the two ends, the upper terminal sends orders and the lower system implements the specific operations, such as data collection, the valve switch and so on. The lower computer will feed the result of collecting data back to the upper computer and display on the LCD. Therefore, the staff can understand the operation of the equipment at the scene very clearly and can deal with the unexpected events very effectively.The main part of this paper is in Chapter III and Chapter V, which focuses on the lower computer hardware systems and the design process of the upper computer software monitoring system, and then explains the program and does the description of the design detailed.The microcontroller is used by the Lower system remote control terminal is AT89S52 single-chip. It is a very high price-performance chip, and at the same time is up to the design requirements. Through the preparation process to achieve lower system initialization and the operation of the corresponding command. Lower system extends the A / D converter module, 8-way switch and pulse measurement. And then extend LCD liquid crystal display and keyboard, to form the human-computer interaction in the lower system, which constitutes a complete hardware platform. The main task of lower system is finished the data collection, the control valve, as well as the determination of speed, and then the data is sent to the MODEM chip Si2457, will convert the digital signal to analog signal in order to transmit in public telephone network. At last, the lower computer will feed the result of collecting data back to the upper computer.The upper computer monitor and management software system is divided into five working areas according to its functions. These five areas are separately test area, site settings area, documents operation area, site operation area, valves settings and data display area. These five working areas are combined and not completely separated, forming a human-computer exchanged interface. Among these areas, Test area are one of the main operations for dial-up connection, dial the required number of dial-up, so that the upper system sent up a command to lower systems for a dial-up connection, and realize the communications of two systems. Site settings and documents operation areas mainly face the community sites to operate, including the site editor, add the site and delete sites, at the same time, in this work area added to documents operations that can operate the data feedback by the lower system, and observe the status of real-time waveform. Site setting area is main the site selection. After adding the site, staff can dial-up connection to the different site to observe the status of this site. Valves setting area mainly sets up numerical values of 8 switches in the lower system, also staff can be required to adjust status on the valves and control the 8 switches of the sites in the lower system. Data display area mainly display 8 status measurements on the monitor system. If the data exceed the limits range, the alarm will be issued.In practice, the system applies to Changchun Heating Company pump station for heat (back) water pressure (temperature), as well as speed control, collection points which transmit data in one every second to monitoring host. Through a pre-set scare, we can be clearly observed the changes of the alarm status and change the on-off status through monitoring system management software. This system works very stable after long time testing. Relative to other means of transmission, this system takes advantages of its convenience, reliability and management without personnel can apply more and more extensively.This design has a point: The use of modem Si2457 and Si3008 Line control chip constitutes interface circuit. Through the serial port can be directly connected with single-chip or computer. Not only facilitate the control of the PC to the chip, but also saves the space occupied by equipment.