今天小编教大家一些查找PLC故障的方法和技巧，小编相信好的方法和技巧能够让你在查找PLC故障的时候事半功倍。

一、PLC的故障类型靠前，外部设备故障靠前，外部设备是什么？就是指与PLC工作过程直接联系的各种开关、 传感器、 执行机构、 负载等。如果这些设备发生故障,就会直接影响 PLC 系统的控制功能。所以维修 PLC的故障之前 ,要分清是外部设备故障,还是 PLC 本身故障。第二，系统故障系统故障：影响 PLC 系统运行的全局性故障。系统故障：分为固定性故障、偶然性故障。故障发生之后,如果可以重新启动使系统恢复正常,不然就是偶然性故障。固定性故障：一般需要更换硬件或软件, 系统才能够恢复正常。第三，硬件故障硬件故障： 系统中的模板、电路损坏而造成的故障。第四，软件故障软件故障包含软件错误、操作错误等。软件故障一般可以通过本身 的自诊断测试功能或者软件来查看。所以，可以看到一般PLC常见故障有电源指示灯不亮，PLC人机无法通讯，PLC IO模块灯亮异常,PLC触点无输出,PLC PO

二、查找一般的PLC故障的基本步骤维修时,先插好编程器,将开关调到 RUN 位置,然后根据六步法步骤查找:（1）假如该信号操控在一个计数器 ，首要查看操控复位的逻辑，然后是计数器信号。按上述2到5步进行。（2）假如施耐德PLC中止在某些输出被鼓励的当地，一般是处于中间状况，则查找引起下一步操作发作的信号（输入，定时器，线川，鼓轮操控器等）。编程器回显现那个信号的ON/OFF状况。（3）输入信号，将编程器显现的状况与输入模块的LED指示作比较，结果不共同，则替换输入模块。假如发现在扩展架上有多个模块要替换，那么，在替换之前，应先查看I/O扩展电缆和她的衔接情况。（4）假如输入状况与输入模块的LED指示指示共同，就要比较一下发光二极管与输入设备（按钮、限位开关等）的状况。假如二者不同，丈量一下输入模块，如发现问题，需求替换I/O设备，现场接线或电源；不然，要替换输入模块。（5）假如信号是定时器，并且停在小于999.9的非零值上，则要替换CPU模块。（6）如信号是线川，没有输出或输出与线川的状况不同，就得用编程器查看输出的驱动逻辑，并查看程序清单。查看应按从左到右进行，找出N个不接通的触点，如没有通的那个是输入，就按第二个和第三步查看该输入点，日是线川，就按第四步和第五步查看。要承认使主控继电器不影响逻辑操作。三、PLC系统维护与故障排除的基本流程总体诊断：根据总体检查流程图，找出故障点的大致方向,然后逐渐细化找出具体的PLC故障。靠前，电源故障诊断如果电源灯不亮需要对供电系统以及电源灯本身进行检查。第二，运行故障诊断电源正常, 运行指示灯不亮, 则说明系统可能因某种异常原因而终止正常运行。第三，输入输出故障诊断输入输出单元是 PLC 与外部设备进行信息交流的通道;输入输出是否正常工作,还与连接配线、接线端子、熔断器等元器件状态有关。WER电源指示灯不亮，PLC模组指示灯不亮,PLC无电源，PLC不通电等。

四、维修的基本顺序靠前，先问再做维修 PLC 时,不要立即直接动手,而是先询问故障发生前后的情况、故障现象;如果对生疏的 PLC 维修,应先了解其工作原理。第二，先清再修在维修PLC 之前,先打开机器清洁 PLC之后，再进行维修工作 。第三，PLC检查先外后内维修PLC 时,先检查外部现象与原因,如果外部正常,则然后检查 PLC 内部。第四，先无后通在没有通电的情况下，判断熔丝是否损坏，在不通电的情况下就可以判断出故障点。如果不能够通过这种方法判断出问题的话,再通电进行检查 PLC的各项 。

Today small make up to teach you some methods and skills to find PLC fault, small make up believe that good methods and skills can let you find PLC fault when twice the result with half the effort.

First, PLC fault type first, external equipment fault first, what is the external equipment? It refers to all kinds of switches, sensors, actuators and loads directly related to the working process of PLC. If these equipment failure, it will directly affect the PLC system control function. So before the maintenance of PLC fault, the first thing to distinguish is the fault of external equipment, or PLC itself fault. Second, system fault system fault: affect the PLC system operation of the global fault. System faults: classified into fixed faults and accidental faults. After a failure occurs, if the system can be restarted to return to normal, or it is an accidental failure. Fixed fault: generally need to replace the hardware or software, the system can return to normal. Third, hardware failure hardware failure: system template, circuit damage caused by the failure. Fourth, software faults software faults include software errors, operating errors, and so on. Software faults can generally be viewed through their own self-diagnostic testing functions or software. Therefore, it can be seen that the power indicator light is not on for common PLC faults,PLC man-machine communication is not possible,PLC IO module light is abnormally on,PLC contact has no output,PLC PO

Two, find the basic steps of the general PLC fault maintenance, first plug the programmer, switch to RUN position, and then according to the six-step method step search :(1) if the signal control in a counter, the first check control reset logic, and then the counter signal. Follow steps 2 to 5 above. (2) if schneider PLC stops in some places where the output is encouraged, generally in the middle, look for the signal (input, timer, thread, drum controller, etc.) that causes the next operation to break out. The programmer echoes the ON/OFF state of that signal. (3) input signal: compare the display status of the programmer with the LED indication of the input module. If the result is different, the input module shall be replaced. If it is found that more than one module needs to be replaced in the extension rack, the I/O extension cable and its connection should be checked before replacement. (4) if the input condition is in common with the LED indication of the input module, the condition of the LED and the input device (button, limit switch, etc.) should be compared. If the two are different, measure the input module, such as the problem found, the need to replace I/O equipment, field wiring or power supply; Otherwise, replace the input module. (5) if the signal is a timer and stops at a non-zero value less than 999.9, replace the CPU module. (6) if the signal is linear and there is no output or the output is different from linear, the programmer should check the output driver logic and the program list. View should be carried out from left to right to find N contacts that are not connected. If the one that is not connected is input, press the second and third steps to view the input point. If the day is the line, press the fourth and fifth steps to view. Allow the master relay to operate without affecting logic. Three, PLC system maintenance and troubleshooting basic process overall diagnosis: according to the overall inspection flow chart, find out the general direction of the fault point, and then gradually refine to find out the specific PLC fault. First, power fault diagnosis if the power lamp is not on, it is necessary to check the power system and the power lamp itself. Second, if the power supply is normal and the indicator light is not on, it means that the system may terminate normal operation due to some abnormal reasons. Third, the input/output fault diagnosis input/output unit is the channel for information communication between PLC and external equipment. The normal operation of the input and output is also related to the state of connecting wiring, terminal, fuse and other components. WER power indicator light is not on,PLC module indicator light is not on,PLC is not powered,PLC is not powered, etc.

Four, the basic sequence of maintenance first, first ask to do the maintenance of PLC, do not immediately direct start, but first ask the situation before and after the fault, fault phenomenon; If the unfamiliar PLC maintenance, should first understand its working principle. Second, first clear and repair before the maintenance of PLC, first open the machine to clean the PLC, and then carry out maintenance work. Third, PLC inspection after the first external maintenance of the PLC, first check the external phenomenon and reasons, if the external normal, then check the PLC internal. Fourth, the first no after pass in the case of no power, judge whether the fuse is damaged, in the case of no power can judge the fault point. If not through this method to determine the problem, then power to check the PLC.