| Summary: | 碩士 === 國立中央大學 === 環境工程研究所 === 91 === The purpose of this research is to design and develop an internet-based SCADA (Supervisory Control and Data Acquisition) system to meet the demand on data collection and transmission of the environmental monitoring stations around this island in the future. The system is composed of two parts：an on-site data collector which is called Site-Server, and a PC-based web server unit at the remote data center. Site-Server has a signal processing unit based on BX-24 microprocessor, an internet protocol processing unit based on siteplayer chip, and other peripheral chips. The system can take both analog and digital signals from different monitoring instruments and transmit calculated data to 8 different subscribed remote databases. Before data are transmitted, the Site-Server stores data in its nonvolatile memories as a backup in case of internet failure. The major functions of this system are listed below：
(1)Internet data transmitting and receiving
(2)Automatic parameter configuration
(3)Preliminary system debugging and rescuing
(4)Multi-users data subscription
(5)Digital signal conversion
(6)Voltage-to-data translation
(7)Inner data-logger
(8)Web-based human-machine interface
Laboratory and on-site tests were put into practice later to evaluate the performances of the system. The laboratory test showed that the steady operation time of Site-Server had reached 95% of the entire period. Other tests such as power failure test, internet service interruption test, and database replication test were also carried out successfully. In field situation, the probability of losing data during transmission was about 0.01%~0.04%, and the access time through internet was about 4~5 seconds. For unknown reasons, Site-Server halted more often in the beginning of the field study. This problem was solved by adding an external watchdog timer. Since then, the system worked steadily.
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