In the long-term maintenance of the PLC controller of Rockwell AB, this paper summarizes the knowledge of some A-B PLC controllers and some practical and effective troubleshooting methods of common faults in actual production.

The hardware series of Rockwell A-B PLC include PLC5, ControlLogix, SLC500, Micrologix, etc; Commonly used communication software includes rslinx, etc; Monitoring interface software InTouch, RSView32, etc; Programming software: rslogix5, rslogix500, rslogix5000. Now, the PLC controller of A-B used in our factory and the troubleshooting methods of common faults are briefly introduced.

There are two types of A-B PLC controllers used by Zhaotong cigarette factory, one is PLC5 and the other is SLC500. Both power modules do not occupy slots, but the difference is that the CPU module of PLC5 does not occupy slots, and the CPU of SLC500 occupies slots, and the former is large and the latter is small. The programming software for PLC5 is rslogix5, while the programming software for SLC500 is rslogix500.

The programming software they use is jointly developed with Microsoft. Its functions and features include:

1. There is a free-form ladder diagram editor, which allows the user to focus on the correctness and error of the program logic without paying attention to the correctness and error of the syntax when writing the program;

2. It has a verifier, which can be used to create an error list, so that it can be modified at a convenient time;

3. With drag and drop editing function, it can quickly move steps between subprograms or between steps in a program;

4. It has query and replacement functions, and can quickly change the value of a specific address or symbol;

5. All file directories on the operation interface of the program can be accessed by clicking the mouse;

6. With data monitoring function, independent data elements can be displayed at the same time to observe their interaction;

7. There is a bar chart function, which can be used to monitor data.

Rslinx software is a copy of rslogix software. When communicating with the CPU on rslogix, you must first run rslinx Lite, which is the interface software used for communication. The module of SLC500 is generally 1746 - & times; ××， The CPU is 1747, and its addressing mode is the selection of slot. The power modules are generally 1746-p1, P2, P3 and P4, of which only P3 is 24 V DC and the rest are 220 V AC input. The CPU of PLC5 is 1785-l20, L30..., * can connect 4 remote I / O channels, * can connect 32 remote I / O nodes (number of physical devices), and the power module is 1771-p7. The addressing modes of PLC5 include 2-slot addressing, 1-slot addressing and 1 / 2-slot addressing. 2-slot addressing means that each physical 2-slot I / O group corresponds to one word (16 bits) in the input / output mapping table. 1 slot addressing means that one physical slot corresponds to one word (16 bits) in the input / output mapping table. 1 / 2 slot addressing means that one physical slot bit corresponds to two words (32 bits) in the input / output mapping table.

Both types of CPUs have key switches, which can be switched between run, prog and rem. run is running, prog is programming, and REM is between the two. It can be defined as run or prog by software. If it is transferred from run to REM, it is run; if it is transferred from prog to rem, it is prog. The lights on the CPU of SLC500 include run, FLT, batt, DH +, force and RS232. When lit, they respectively represent normal, fault, insufficient battery, DH + communication normal, forced output and serial communication. When the lamp batt on the CPU of PLC5 is on, it indicates that the battery voltage is insufficient; Proc green indicates operation and red indicates fault; When forc is on, it indicates that the forced I / O is valid; When comm is on, it indicates that the communication status is normal. DH + communication link is adopted for the communication between them, including the remote adapter card. The upper computer communicates with the CPU by running rslinx Lite or rslinx gateway software on the computer. RS-232 or DH + communication link can be used for local programming, and DH + or Ethernet can be used for remote programming.

The programs in AB's PLC5 and SLC500 are generally not easy to lose, so the failures are generally manifested as communication failures and module failures. The performance of PLC hardware of AB is relatively stable, so there are few failures of PLC in dry ice line. The following are common:

1. The analog input value is displayed as a certain value and will not change. One situation occurs before startup. In this case, first check whether the red light of the analog input module is on. If it is on, turn off the power supply and adjust the module to check whether the module is burnt. If it is broken, replace it. If it is not broken or the light is not on, it is a data transmission fault or a scanning fault. In this case, the PLC is generally powered on again to recover. The other is during operation, which is generally caused by the failure of CPU module and analog module. Sometimes, it can be recovered after power on again. If it cannot be recovered, the CPU module may be broken.

2. If the operation command is not executed, that is, the operation does not work. There are two possibilities. One is that the conditions required for the operation are not met, so the operation does not work. The other is that the program is in its own closed cycle, i.e. dead cycle or overflow of scanning time, resulting in output prohibition, or communication failure. In this case, the system can be stopped and restarted first, or the system can be recovered after power off and then switched to automatic and started. If it cannot be recovered, the PLC can be recovered after power on again.

3. All outputs of the PLC are not available, that is, the indicator lights on the modules corresponding to all points that should have outputs are not on. There is only one possibility of this fault, that is, the 24 volt power supply provided by the output module is not available. One is that the conditions for the intermediate relay to supply power to the output module are not met. The other is that the coil of the intermediate relay is burnt or the contact is poor.

4. The signal can not be received for a long time, resulting in a control unit unable to operate. This situation belongs to communication failure or data transmission failure. Generally, it can be recovered by repeating the steps of generating the signal.

5. The green light of all input and output modules of PLC is not on. In this case, first check whether the input of the power module has 220V AC. if not, check whether the power supply transformer is good or bad. If yes, the power module is broken.

6. In the process of operation, the on-line equipment suddenly stops moving, that is, the PLC suddenly "crashes". In this case, first look at the status of the PLC. If the lights on all modules are not on, it is most likely that the power module of the PLC is broken; If the lights on all modules are on again when you press the CPU with your finger, then unplug the CPU and plug it in. Generally, the fault can be eliminated. Another case is that the input and output points of the input and output modules of some blocks are not displayed. In this case, when troubleshooting the input and output modules, the fault can be generally eliminated by plugging the CPU.

7. The DH + or comm light on the CPU flashes or is red, which is a communication fault. In one case, DH + cable is broken or socket is loose. Check and handle DH + cable and socket until the fault disappears; The other case is that the communication address of the CPU is wrong or changed. At this time, you must enter rslinx and click the communication configuration icon to reconfigure the address of the upper computer or PLC icon with the Red Cross until the Red Cross disappears.

In short, various PLC failures will be encountered in the actual production process. Although the PLC hardware performance of AB is relatively stable and the possibility of failure is very small, for our electrical maintenance personnel, no matter whether it is abplc or Siemens PLC, as long as we use it, we must master it. We are always lagging behind in the knowledge of software and hardware of PLC programmable controller. Only through continuous learning, can we master some PLC maintenance methods and common troubleshooting methods, so that PLC can better serve us.