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可编程控制器(PC) 可以看成是在系统软件支持下的一种扫描设奋,循环扫描的操作执行着由系统软件和用户程序所规定的任务。在介绍PC的基本工作原理之前先比较一下传统的继电器控制方式和PC控制方式. 图1是一个简单的继电器控制回路,用以控制气动系统电磁阀的励磁线圈。当按动起动按扭QA时,继电器J1动作、使气缸的活塞杆向前运动,并由J1的触点保持自身的线圈处于继续通电状态。与此同时,时间继电器SJ动作,经过预先设定的时间延时后,继电器J2动作,使电磁阀换向,活塞杆返回原位。
A programmable logic controller (PC) can be seen as a type of scanner supported by system software that performs the tasks specified by system software and user programs. Before introducing the basic working principle of the PC, compare the traditional relay control method and PC control method.Figure 1 shows a simple relay control circuit to control the excitation coil of the pneumatic system solenoid valve. When pressing the start button QA, the relay J1 action, the cylinder piston rod forward movement by the J1 contact to maintain its own coil in the continued energized state. At the same time, the time relay SJ action, after a predetermined time delay, the relay J2 action, the solenoid valve to reverse the piston rod back to its original position.