Abstract
A 40L/h helium liquefier has developed by Technical Institute of Physics and Chemistry, Chinese Academy of Sciences. It uses ATEKO’s electromagnetic bearing turbine expanders and KAISER’s helium screw compressor as its main components. Its control system uses the SIEMENS PLC S7-300 and its related programming software Step7 V5.5 and process monitoring software WinCC V7.2. The control strategies of the machine mainly include three parts. One is to ensure the compressor supply enough power and refrigeration mass flow; another is to ensure the turbines supply enough refrigeration capacity; and finally is to make the dewar cool down to the set temperature and the refrigeration material change to liquid helium stably. All of these are achieved by adjusting various control valves of the system. This paper will detailed describe the control strategies of these parts, and give the PID control parameters.
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