S5 PLC has self-diagnostic ability. When module function error occurs, it can often alarm and react according to the pre-program. It can be judged by the fault indicator. When the power supply is normal, the indicators also indicate normal, especially when the input signal is normal, but the system function is not normal (the output is no or disorder), in accordance with the principle of easy first, then hard, first soft then hard, first check whether the user program appears problem. The user program of S5 is stored in the RAM of PLC and is volatile during power failure. When the backup battery fails and the system power fails, the possibility of program loss or disorder is very high. Of course, strong electromagnetic interference will also cause program errors. . A PLC recovery program with an EPROM memory card and slot is quite simple. Generally, you can solve the problem after copying the program on the EPROM card back to the PLC; users without EPROM sub-cards should use the PG online function to send the correct program to PLC. It should be particularly noted that sometimes simple program coverage cannot solve the problem. In this case, it is quite necessary to always clear the user program in RAM before re-copying the program. By dialing the "RUN" and "ST" switches on the PLC in the order of RUN--ST--RUN--ST--RUN or executing "Object-Blocks-Delete--inPLC-on the PG" The "allblocks-overall-Reset" function completes the total clearing of programs in RAM.
In addition, the programs stored in EPROM are not foolproof. I believe that the programs on EPROM can sometimes cause confusion for maintenance. Therefore, it is very important to check and check the programs in EPROM regularly, especially the backup programs in PG.
Maintenance example: The device cannot start after being powered on. After checking, the engineer thinks that the program is wrong, and naturally inserts the EPROM card into the PLC. After the total is cleared, the program is copied and restarted after completion. The fault remains the same. Because the program is not large, the program on the EPROM is read out one by one, and the instructions in the manual After checking, it is found to be exactly the same. After repeated copying is invalid, it is regarded as PLC hardware failure. We use PG to call up the backup program and compare it with the program on EPROM. The result statement instruction table is the same, but the program storage address has changed. After the backup program is sent to the PLC, the device runs normally. It can be seen that the program on the EPROM also has an error, and the problem is solved after being erased with ultraviolet light.
2. PLC hardware failurePLC hardware faults can be found relatively intuitively, and the basic method of maintenance is to replace the module. Judging the faulty module according to the fault indicator and fault phenomenon is the key to overhaul, and blind replacement will bring unnecessary losses.
(1) The power module is faulty.
For a working power module, the working indicators such as "AC", "24VDC", "5VDC", "BATT", etc. should be solid green. Which lamp has changed its color or flickered or turned off? Indicates that there is a problem with the power supply of that part. The "AC" light indicates the PLC's total AC power supply. When the "AC" light is off, most of the power is off, and the entire PLC stops. At this time, you should check whether the power supply fuse is blown. Replace the fuse with a fuse of the same specification and type. If there is no imported fuse of the same type, use a fast fuse with the same current. If the fuse is burned repeatedly, it means that the circuit board is short-circuited or damaged. Replace the entire power supply. When the "5VDC" and "24VDC" lights are off, there is no corresponding DC power output. When the power deviation exceeds 5% of the normal value, the indicator flashes. At this time, although the PLC can still work, it should be paid attention to. If necessary, stop the maintenance. The "BATT" color-changing light is a backup power indicator. The green color is normal, the yellow power is low, and the red color is faulty. When the yellow light is on, the backup battery should be replaced. The manual stipulates that the lithium battery should be replaced once every two to three years. When the red light is on, it indicates that the backup power system is faulty and the entire module needs to be replaced.
(2) The I / O module is faulty.
The input module is generally composed of a photoelectric coupling circuit; the output module has relay output, transistor output, photoelectric output, etc. according to different models. Each input and output has a corresponding LED indicator. If there is an input signal but the point is not on or if there is an output but the output light is off, you should suspect that the I / O module is faulty. The input and output modules have 6 to 24 points, and it is not economically advantageous to replace the entire module just because one point is damaged. The usual practice is to find a replacement point, and then change the corresponding address in the program. However, it should be noted that the larger the program, the more difficult it is to find a specific address. It is particularly emphasized that no matter whether the input module or the output module is replaced, the PLC must be powered off. S5 live plug-in modules are absolutely not allowed.
(3) The CPU module is faulty.
The CPU module of the general-purpose S5 PLC often includes communication interface, EPROM slot, running switch, etc., the fault is more concealed, because the cost of replacing the CPU module is very large, so its failure analysis and judgment should be especially careful.
Maintenance example: When a PLC is turned on, the switch cannot be turned to RUN state. The error indicator flashes first and then turns on. The fault remains the same after power-off reset. It runs normally after replacing the CPU module. During the chip-level maintenance, the CPU was replaced but the fault light still blinked. The function did not return to normal until the communication interface board was replaced.
3. The peripheral circuit is faulty.According to relevant literature reports, the failure rate in the PLC control system is: CPU and memory 5%, I / O modules 15%, sensors and switches 45%, actuators 30%, wiring and other aspects 5 %, It can be seen that more than 80% of the faults appear on the peripheral lines. The peripheral circuit consists of on-site input signals (such as button switches, selector switches, proximity switches and some sensor output switches, relay output contacts or analog-to-digital converter converted analogs, etc.) and on-site output signals (solenoid valves, relays, contacts Devices, motors, etc.), as well as wires and terminals. Loose wiring, damaged components, mechanical failure, interference, etc. can cause peripheral circuit failures. Care should be taken when investigating. The replacement components must be high-quality devices with reliable performance and high safety factor. Some powerful control systems use fault code tables to indicate faults, which greatly facilitates the analysis and removal of faults and should be used well.
Example of maintenance: The control system of the underwater pelletizer has failed. The engineer found that I5.4 has no input and Q7.0 has no output, and the pelletizer cannot be turned on. After inspection, it was found that the signal converter and the proximity switch were damaged at the same time, and they were normal after replacement. Such faults have certain concealment, and they should be eliminated step by step with the help of multimeters, system schematics and logic diagrams when troubleshooting.
The SIMATICS5 control system integrates digital circuits, analog circuits, relay circuits and computer technologies, and has high stability and reliability. However, once a failure occurs, it will cause a large loss of the entire system shutdown, maintenance is difficult, and maintenance costs Higher, the maintenance tools used in addition to multimeters sometimes use oscilloscopes or even computers, which requires maintenance personnel to have high professional skills, and a certain foreign language and computer skills, only after understanding and familiar with the entire system can common The fault can be judged quickly and eliminated quickly, and the maintenance cost can be reduced as much as possible to ensure the normal stability of the system.
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