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Siemens PLC S5 controlling system failures and maintenance

S5 PLC with self-diagnostic capability, the module features an error occurred when the police are often able to respond according to pre-process, through the fault indicator can judge. When the power supply normal, the indicator light indicate normal, especially Shuru signal normal, Dan Jitonggongneng Bu normal (Shu Chu Wu or disorder) O'clock, in line with the easier, the first soft, then hard to repair Yuanzeshouxian Jianchayonghu Cheng Xu Shifouchuxian problem. S5 PLC user program stored in the RAM, is the power-down volatile, when back-up battery system power fault slip occurs, the program is missing or the possibility of disorder on the great, of course, strong electromagnetic interference will lead to error, . There EPROM memory card and slot PLC recovery program is quite simple to program EPROM card copy back to normal after the PLC can solve the problem; no EPROM daughter card users must use the online function of PG will be sent to the correct procedure PLC on. Need of special note is that sometimes simple procedure covers not solve the problem, then re-copy the program in the former clear about RAM in the user program is quite necessary. By the PLC on the "RUN" "ST" switch by RUN --- ST --- RUN --- ST --- RUN order call again or PG on the implementation of "Object-Blocks-Delete --- inPLC- allblocks --- overall-Reset "function is completed the total RAM in the process clear. In addition, the program stored in the EPROM is not foolproof, over-confident on the program EPROM will repair sometimes confusing. Therefore, regular inspection check EPROM in the process, particularly in the backup program on the PG was of particular importance.

Maintenance Examples: device can not start after power. After checking that the program engineers wrong, it is natural to EPROM card into the PLC, the total clearing process after the copy, complete restart, fault still, because of a small, one by one to the program EPROM read out the instructions and manual checked and found exactly the same, repeat the copy that is the PLC after failed hardware failure. PG we will bring up the backup process, and the EPROM on the procedures to compare the results statement, the same instruction table, but the program storage address has changed, the backup program sends to the PLC after the device operating normally. EPROM on the procedures can be seen an error, re-written after UV erase solve the problem.

Second, PLC hardware failure

PLC hardware failure can be more intuitive to find the basic method of repair is to replace the module. According to the phenomenon of fault and fault indicator to judge fault module is the key to maintenance, replacement of the blind will lead to unnecessary losses.

(1) power supply module failure.

        A working electrical module, the work of the above indicator, such as "AC", "24VDC", "5VDC", "BATT" and so should be the long bright green, which changes the color of light or flashes or goes out on said that part of the power supply problems. "AC" light that the exchange of the total power PLC, "AC" light does not work when the most no power to stop the PLC. Then you should check the power fuse is blown, replace the fuse is to apply the same type of fuse with the specifications, no imports of the same type of fuse to use the current time instead of the same fast fuse. If repeated burning fuse board short description or damaged, replace the entire power supply. "5VDC", "24VDC" lights out that without the appropriate DC power output, when the power deviation of 5% above the normal level indicator light flashes, then although the PLC can still work, but attention should be paid and, if necessary downtime. "BATT" is the reserve power indicator light color, normal green, yellow, low power consumption, the red fault. Should be replaced when the yellow light is back-up battery, manuals, replacement Li-ion battery provides two to three years time, when the red light is that the backup power system failure, also need to replace the entire module.

(2) I / O module failure.
Input modules are generally composed of optical coupling circuit; output module with relay outputs according to different models, transistor output, optical output. Each point has a corresponding input-output LEDs instructions. With the input signal but the point is not lit or identified, but the output does not light output should be suspected when the I / O module failure. Input and output modules have from 6 to 24 points, one point if only because of the damage on the replacement of the module is not economically viable. The usual practice is to find an alternative backup point, and then the corresponding change in the program address. But pay attention, the program is more difficult to find specific addresses. Particular emphasis was placed, either to replace or change the input module output module, to be in power in the conduct of PLC, S5 hot plug module is absolutely not allowed.

(3) CPU module failure.
Universal S5 PLC's CPU module often includes communication interface, EPROM slot, run switch, hidden faults more because the cost of replacement CPU module big, so its failure analysis, determine to be especially careful.
Table 1-1 cases out of the CPU module and treatment of common faults.

 
        Maintenance Examples: a PLC can not be closed when the power switch to the RUN state, error lights start flashing light is, power reset the malfunction persists, replace the CPU module is operating normally. During chip-level maintenance, replacement of the CPU, but still kept flashing fault lights, to an excuse to replace the board after the communication function returned to normal.

Third, the external line fault.

According to the literature, the PLC control system malfunction rate: CPU and memory accounting for 5%, I / O modules 15%, 45% sensors and switches, actuators 30%, 5 wiring, and other aspects of %, more than 80% of the fault can be seen in the external circuit. External line input signal from the site (such as button switches, selector switches, proximity switches and some amount of sensor output of the switch, relay output contacts or ADC analog conversion, etc.) and field output (electromagnetic valves, relays, , contactors, motors, etc.), as well as conductors and terminals, etc. Loose wiring, damaged components, mechanical failure, interference can cause the external circuit fault, troubleshoot to carefully replace the components to use and reliable high-quality factor of safety devices. Some powerful control system fault code table, said fault, the fault of the great conveniences of exclusion, should make good use of.
 

Maintenance Examples: underwater granulator control system failure, engineers found that I5.4 Q7.0 no output without input lead, granulator can not open. After checking, the signal converter and close to the switch also damaged, the normal replacement. As such failure would have a certain degree of secrecy, troubleshooting multimeter when using the system schematic and logic diagram progressively excluded.

SIMATIC S5 control system combines digital circuits, analog circuits, relay circuits and computer technology, high stability and reliability, but once the system failure will result in downtime greater losses, repair and maintenance costs will be difficult also higher, with the repair tools in addition to the oscilloscope or multimeter sometimes use the computer, which requires maintenance personnel with high professional skills, and have some foreign language and computer skills, only to understand and become familiar with the whole system can one failure to achieve a common judge quickly ruled out quickly, and reduce maintenance costs as much as possible to ensure the system's normal and stable. (For reference only)