179-01第四类故障点可能发生在PLC系统中的子设备这类设备如接线盒、线端子、螺栓螺母等处。这类故障产生的原因除了设备本身的制作工艺原因外还和安装工艺有关
，如有人认为电线和螺钉连接是压的越紧越好，但在二次维修时很容易导致拆卸困难，大力拆卸时容易造成连接件及其附近部件的损害。长期的打火、锈蚀等也是造成故障的原因。根据工程经验，这类故障一般是很难发现和维修的。所以在设备的安装和维修中一定要按照安装要求的安装工艺进行，不留设备隐患。
5、第五类故障点是传感器和仪表
这类故障在控制系统中一般反映在信号的不正常，这类设备安装时信号线的屏蔽层应单端可靠接地，并尽量与动力电缆分开敷设，特别是高干扰的变频器输出电缆，而且要在PIC内部进行软件滤波。这类故障的发现及处理也和日常点巡检有关，发现问题应及时处理。
6、第六类故障主要是电源、地线和信号线的噪声(干扰)
问题的解决或改善主要在于工程设计时的经验和日常维护中的观察分析。
要减小故障率，很重要的一点是要重视工厂工艺和安全操作规程，在日常的工作中要遵守工艺和安全操作规程，严格执行—些相关的规定，如保持集中控制室的环境等等，同时在生产中也应加强这些方面的管理。
过程控制系统本身是一个完整的系统，所以在分析故障或处理故障时也要注意系统性，单独的对某一部分的优化有时并不能提高系统的整体性能。如过分追求元器件的精度而不考虑实际的需要以及和相关设备精度的匹配，将徒然增加系统成本。在日常维护中也有过把系统越改越复杂的现象，如采用复杂的控制方式和设备来实现本可以用简单装置来实现的控制，违背了经济、简单、实用的原则，并可能会增加故障率，这也是要注意的地方。
2. The second type of fault frequently occurs on equipment such as valves or rams
Because the relative displacement of the actuator of such equipment is relatively large; Or the transmission structure is complex, and if the mechanical, electrical, hydraulic and other
s are not in place, errors or faults will occur. Under long-term operation, if there is no operation and maintenance, it is easy to cause jamming, blocking and leakage of valve body parts. Therefore, when the system is running, it is necessary to strengthen the patrol inspection of such equipment and timely handle the problems found. Our factory has established a strict point inspection system for such equipment, regularly checking whether the valve is deformed, whether the actuator is flexible and available, and whether the controller is effective, which well ensures the effectiveness of the entire control system.
3. The third type of fault point may occur on some elements or equipment in switch, limit position, safety protection and field operation
The reason may be due to long-term wear, or corrosion and aging due to long-term use. For example, the distribution cart on the kiln tail ball storage of the production line moves frequently, and the dust on the site is large, so the contact of the proximity switch is deformed, oxidized, and blocked by dust, resulting in poor contact of the contact or insensitive action of the mechanism. The treatment of this kind of equipment failure is mainly reflected in regular maintenance to keep the equipment in good condition at all times. For limit switches, especially those on heavy equipment, in addition to regular maintenance, multiple protection measures should be added in the design process.
