07KT92 GJR5250500R0902 ABB

It shows that the faults in the programmable controller CPU,memory,system bus and power supply only account for 0.5%of the total system faults,and the faults in the I/O modules only account for 4.5%of the total system faults.It can be seen from the analysis that usually,in practical applications,the following aspects are often considered:

(1)Pay attention to the selection of external equipment and shorten a lot of maintenance time.

(2)Protection of data and programs.Most PLC control systems use the RAM supported by lithium batteries to store the user’s application programs.Generally,the life of a battery is about 5 years,and all the application programs will be lost after it is used up.Therefore,some important places often use memory cards to store user applications.Keep program and technical data as archives.for backup use.

(3)Certain anti-interference measures should be taken for installation and wiring.Generally,the PLC power supply is powered by a 1:1 isolation transformer with a shielding layer.When used in an environment with strong interference sources,the shielding layer and the PLC floating terminal should be grounded,and the area ofthe grounding wire should not be less than 2mm2.The grounding wire should be independent,and cannot be grounded in series with other equipment.PLC power lines,I/O power lines,input and output signal lines,and AC and DC lines should be routed as far as possible.Switch signal lines and analog signal lines should also be routed separately,the latter should be shielded,and the shielding layer should be reliably grounded,etc.

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说明发生在可编程控制器CPU、存储器、系统总线和电源中的故障只占系统总故障的0.5%，而发生在I/O模板中的故障也只占系统全部故障的4.5%。分析可见，通常，在实际应用中往往从以下几方面来考虑：

(1)要注意外部设备的选择，缩短大量的维修时间。

(2)数据和程序的保护。大部分PLC控制系统都采用锂电池支持的RAM来存储用户的应用程序，一般一支电池的寿命为5年左右，用完后应用程序将全部丢失。因此一些重要的地方常采用存储卡来存储用户的应用程序。将程序及技术资料作为存档保存起来。以防后备使用。

(3)安装与布线要采取一定的抗干扰措施。一般PLC电源都采用带屏蔽层1：1隔离变压器供电，在有较强干扰源的环境中使用时，应将屏蔽层和PLC浮地端子接地，接地线面积不能小于2mm2。接地线要采取独立的方式，不能用与其它设备串联方式接地。PLC电源线，I/O电源线，输入、输出信号线，交、直流线都应尽量分开布线。开关量信号线与模拟量信号线也应该分开布线，后者应用屏蔽线，并且将屏蔽层可靠接地等等。