求翻译：梯形图（LAD: Ladder Logic ）：是在继电器控制电气原理图基础上开发出来的一种直观形象的图形编程语言，沿用了继电器、接点、串并联等术语和类似的图形符号，与电气操作原理相对应，具有直观性和对应性，易被电气人员掌握，是编程应用的主选用户语言 。是什么意思？

Ladder diagram (LAD:Ladder Logic): is to control electric schematic diagram of relay developed on the basis of a visual image of the graphics programming language, follows the relay, contact, terms and similar graphical symbols such as series parallel, and electric operation corresponds to the princ

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Trapezoidal chart (LAD: Ladder Logic): Is one kind of direct-viewing image graph programming language which develops in the black-white control electricity schematic diagram foundation, has continued to use terminology and the similar graph mark and so on relay, contact, series-parallel connection,

Ladder diagram (LAD:Ladder Logic): is to control electric schematic diagram of relay developed on the basis of a visual image of the graphics programming language, follows the relay, contact, terms and similar graphical symbols such as series parallel, and electric operation corresponds to the princ

Ladder diagram (LAD:Ladder Logic): is to control electric schematic diagram of relay developed on the basis of a visual image of the graphics programming language, follows the relay, contact, terms and similar graphical symbols such as series parallel, and electric operation corresponds to the princ