3708E-般交流电压波动在 + 10%(+ 15%)范围内，可以不采取其它措施而将PLC直接连接到交流电网上去b.中央处理单元(CPU)中央处理单元(CPU)是PLC的控制中枢。它按照PLC系统程序赋予的功能接收并存储从编程器键入的用户程序和数据;检查电源、存储器、/O以及警戒定时器的状态，并能诊断用户程序中的语法错误。3708E当PLC投入运行时， 首先它以扫描的方式接收现场各输入装置的状态和数据，并分别存入I/O映象区,然后从用户程序存储器中逐条读取用户程序，经过命令解释后按指令的规定执行逻辑或算数运算的结果送入/O映象区或数据寄存器内。3708E等所有的用户程序执行完毕之后，后将I/O映象区的各输出状态或输出寄存器内的数据传送到相应的输出装置，如此循环运行，直到停止运行。3708E为了进一步提高PLC的可靠性， 近年来对大型PLC还采用双CPU构成冗余系统，或采用三CPU的表决式系统。 The fluctuation of AC voltage in 3708E is within the range of+10% (+15%), and the PLC can be directly connected to the AC network without taking any other measures. The central processing unit (CPU) is the control center of the PLC. It receives and stores user programs and data input from the programmer according to the functions assigned by the PLC system program; Check the status of power supply, memory,/O, and alert timer, and be able to diagnose syntax errors in user programs. When the 3708E PLC is put into operation, it first receives the status and data of various input devices on site through scanning, and stores them in the I/O image area respectively. Then, it reads user programs one by one from the user program memory, interprets commands, and executes logical or arithmetic operations according to the instructions. The results are sent to the/O image area or data register. After all user programs such as 3708E are executed, the output states or data in the output registers of the I/O image area are finally transmitted to the corresponding output devices, and the operation is repeated until it stops. In order to further improve the reliability of PLCs, 3708E has also adopted redundant systems with dual CPUs or voting systems with three CPUs for large PLCs in recent years
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