附录A：外文文献.doc

附录A：外文文献.doc附录A：外文文献
Based on PLC control system of waterworks ponds
The control system of the cryogenic facility in the waterworks ponds system has been replaced by employing the PLC (Programmable Logic Controller) and SCADA (Supervisory Control And Data Acquisition)system< The original control system was constructed about 20 years ago by specifying the DCS (Distributed Control System) computer to deal with 〜400 feedback loops. Recently, troubles on this control system have increased due to itsage-induced deterioration. To maintain the high reliability of the cryogenic facility, a new control system has been planned with the PLC and SCADA systems. Their attractive features include high market availability and cost-effectiveness, however, the use of PLC for such a large facility with 〜400 feedback loops has not been established because of insufficient processing capability of the early PLC.
Meanwhile, the recent progress in the PLC enables to use the FBD (function block diagram) programming language for 500 function blocks. By optimizing the function blocks and connecting them in the FBD language, the feedback loops have been successfully replaced from DCS to PLC w让hout a software developer.
Moreover, an oscillation of the liquid He level, which often occurs during the cooldown mode of the cryopumps, can be automatically stabilized by easily adding a new processprogram in the PLC. At p