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恒力液压机能实现加载力、位移或其速率的恒定。测控系统以小型PLC为控制核心，位移测量采用光栅尺，并采用PLC中断程序进行4倍频处理以提高测量精度，压力测量采用带有通讯功能的高性能调理转换模块代替性能有限的PLC的A/D模块，显著提高了测量分辨率和精度。自编的PID算法充分发挥了PLC的性能，提高了闭环控制精度。液压机的参数设定、显示由触摸屏完成，而长期的数据保存、输出由上位机实现。试验结果表明，测控系统达到了设计要求。“,”Constant force hydraulic press can be used to realize constant displacement,force and those rates. The miniature PLC was used as the core of the measurement and control system. The grating ruler was applied to measure displacement,and its measure-ment accuracy was improved by method of fourfold frequency produced by interrupt program. Measuring resolution and accuracy of the pressure were improved substantially by high-performance conditioning conversion module with communication interface,instead of PLC’s A/D module of low performance. Performance of PLC was brought into full play,and closed-loop control accuracy was improved by self made PID program. Setting and display of press parameters were finished by human machine interface. These were stored for a long and outputted by the host computer. The results show that the measurement and control system meets the design requirements.