PLC control system of the general structure and fault type

PLC control system is mainly composed of input sections, CPU, sampling, output, control and communication components, as shown in figure 1. Input part includes the control panel and input template; Sampling part includes sampling control template, AD transform template, and sensors; The CPU is the core of the system, complete the receiving data, processing data, the output control signal; Output part using DA template system, the output signal is converted to analog signal, through the power amplifier drive actuators; Most system directly to the output signal to the output template, driven by the output template actuators; Part of the communication is communication templates and upper unit into. Because PLC itself little probability of fault, fault mainly from the peripheral components in the system, so its fault can be divided into the following several kinds: ( 1) Input the fault, i. e. , operator error; S sensor fault; S actuator failures; S PLC software failure the failure, can use the appropriate fault diagnosis method for real-time monitoring, analysis and use software to forecasting and the fault. Fault diagnosis method of PLC control system of PLC control system fault macroeconomic diagnosis fault diagnosis is based on experience, with reference to the environment and phenomenon of breakdown to determine the location and cause of failure. PLC control system of the macroscopic fault diagnosis method is as follows: s whether it is caused by improper use fault, such as belong to this type of fault, depending on the usage can judge the fault type and location. Common improper use include power supply failure, terminal connection failure, the failure of template installation, field operation. S fault, if not use may be accidental fault or failure which caused by the system for a long time. For this type of failure can press PLC failure distribution, in turn, judgment of failure. First checks are connected to the actual process of sensor, the detection switch, actuator and load if there is a failure, and then to check whether there is fault of PLC I/O templates: the last check whether the PLC CPU is defective. S failure in check PLC itself, may refer to the indicator lights on the PLC CPU template template and power supply. S to take the steps above also check out the fault reasons and positions, may be system design error, at this time to review the system design, including hardware design and software design. The fault self diagnosis of fault self-diagnosis of PLC control system is the important aspect of system maintainability design and important problem is to improve the system reliability must be considered. Since the diagnosis software method judging fault section and main reason. The content of the different control system since the diagnosis. PLC self-diagnosis of PLC has a strong ability, when their own failures, or peripheral equipment failure, are available on the PLC has the indicator for the diagnosis of light-emitting diodes (leds) on and off to find. The overall flow chart of diagnosis based on overall check to find fault point direction, progressive elaboration, to find out the specific fault, as shown in figure 2. Power supply fault diagnosis power light is not on, need for power supply system for diagnosis. If the power light is not on, first check whether there is electricity, if there is electricity, the next step is to check whether the power supply voltage, without appropriate adjust the voltage, if the supply voltage, the right is the next step is to check whether the fuse is burnt out, if the damage will replace the fuse check the power supply, if you don't burn out, the next step is to check whether the connection is wrong, if the connection is correct, it should be replaced the power supply parts. Operation fault diagnosis of power supply is normal, the light is not bright, because system has some abnormal termination of the normal operation. Check the process as shown in figure 3. Figure 3 running flow chart of fault diagnosis is input and output of PLC input/output fault diagnosis information communication channels with external devices, whether its normal work, in addition to related to the input and output unit, also with the connecting wiring, terminal blocks, fuse components such as state. Input problems, the first check whether the LED power indicator response field components ( Such as buttons, travel switch, etc. ) 。 If the input device are incentives ( The field components have action) While the indicator is not bright, the next step should be reach check voltage of the input terminal of the correct voltage value. If the voltage value correctly, can replace the input module. If an LED indicator logic dimming, and according to the programming device monitors, processor, did not identify the input, the input module there may be a failure. If the module does not solve the problem and replace are connected correctly, may be I/O rack or communication cable out of the question. In output failure, should first check whether the output device response LED status indicator. If the output contact electricity, module indicator lights, the output device does not respond. So, first check the fuse or replace the module. If the fuse in good condition, replace the module has failed to solve the problem, should check the field wiring. If according to the programming device monitor displays a follower were ordered to get through, but the indicator closed, should replace the module. In the diagnosis of input/output failure, best method is to distinguish whether the module itself, or the problems of the field connections. If have a power indicator, indicator and logic module fault is easy to find.