1)According to the I/O device and the I/O allocation table and ladder diagram of the PLC,find out the input and output relays,and give the text code corresponding to the control circuit of the relay contactor.
2)Mark the text code of the corresponding input device and output device next to the coil and its contacts of the ladder diagram programming element.
3)The ladder diagram is decomposed into several basic units,each basic unit can be a program segment(including one output element)or several program segments(including several output elements)of the ladder diagram,and each basic unit is equivalent to a relay Contactor Control
a branch of a circuit.
4)The corresponding relay contactor control circuit can be drawn for each step.
5)When a programming element is energized,all its moving contacts are closed,and all moving contacts are disconnected.When a programming element loses power,all its closed moving contacts are opened(reset),and all opened moving contacts are closed(reset).Therefore,after the programming element is electrified and de-energized,it is necessary to find out all its moving contacts and moving contacts,and analyze its influence on the corresponding programming element.
6)Generally speaking,the ladder diagram can be read from the first natural line of the first block.The first natural behavior program start line.Press the start button to turn on an input relay,all the moving and closing contacts of the input relay are closed,and the moving and breaking contacts are disconnected
1)根据I/O设备及PLC的I/O分配表和梯形图,找出输入、输出继电器,并给出与继电器接触器控制电路相对应的文字代号。
2)将相应输入设备、输出设备的文字代号标注在梯形图编程元件线圈及其触点旁。
3)将梯形图分解成若干基本单元,每一个基本单元可以是梯形图的一个程序段(包含一个输出元件)或几个程序段(包含几个输出元件),而每个基本单元相当于继电器接触器控制
电路的一个分支电路。
4)可对每一梯级画出其对应的继电器接触器控制电路。
5)某编程元件得电,其所有动合触点均闭合、动断触点均断开。某编程元件失电,其所有已闭合的动合触点均断开(复位),所有已断开的动断触点均闭合(复位)。因此编程元件得电、失电后,要找出其所有的动合触点、动断触点,分析其对相应编程元件的影响。
6)一般来说,可从第一个程序段的第一自然行开始识读梯形图。第一自然行为程序启动行。按启动按钮,接通某输入继电器,该输入继电器的所有动合触点均闭合,动断触点均断开
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