We have two lines equipped with S7-414 PLCs that are running the same program. Our Maxon valves are used to kickstart the combustion process, which is closely monitored through safety blocks. However, there is an issue that arises occasionally when attempting to relight the furnaces: the PLC enters STOP mode when opening the final Maxon valve out of six, with no consistent pattern in which valve triggers the issue. Our OEM has investigated the problem with assistance from Siemens, but a solution has not been found yet. The diagnostic fault buffer indicates data corruption in the safety program before outputting to the F I/Ologics. After performing a warm restart, the system goes back to normal operation, but this issue may persist a few times before all the Maxon valves can be opened smoothly. It is worth noting that the Maxon valves are 110VAC, while the PLC control runs on 24VDC.
If the F-CPU enters STOP mode and shows a "Data corruption in the safety program..." message in the diagnostics buffer, what should you do? When it comes to Siemens and S7 safety expertise, it's recommended to reach out to Siemens Support directly rather than going through an intermediary. Assessing the competence of the OEM is crucial in such situations. Dealing with safety issues is never simple; it requires expertise and prompt action.
Our OEM has connections with former Siemens employees, who one would expect to have the expertise to provide a solution. However, it is surprising that they were unable to deliver a resolution.
Check out this screenshot of the diagnostic buffer, which provides valuable insights into system performance and troubleshooting.
In order to conduct a thorough analysis of the issue, access to the code beyond the diagnostic buffer entry is necessary. Feel free to send the code via private message if you would like an additional perspective on the matter.
This is indeed a tricky situation. I might be off track, but have you checked if there's a potential voltage drop occurring when all Maxon valves are deployed? Though the valves are running on 110VAC, it could interfere with the 24VDC control power for the PLC if there's a significant load change. Also, the seemingly random nature of the issue might be connected to external factors such as load on your electrical supply or temperature changes in your facility. A temporary backup supply for your PLCs might be worth considering to rule out power-related issues. Additionally, if there are different operating conditions when this problem arises, looking for any patterns in those conditions might help isolate the problem.
This definitely sounds like a tricky situation. If it's not a hardware issue, it could perhaps be a problem with the timing in your control sequence. Corruption in the safety program and the seemingly random nature of the issue might suggest that a conflict or race condition is occasionally occurring during your safety routine. One suggestion might be trying to add some deliberate delays into your program, thus staggering the process slightly to mitigate simultaneous requests or conflicts. Even if your PLC can handle parallel processing, there could still be potential for timing issues due to the different power levels of your Maxon valves and your PLC control as you noted. Ultimately, while this isn't a permanent solution, it might help provide some insights into this intermittent problem while you find a long-term fix with your OEM and Siemens.
From my understanding, data corruption in the safety program could be due to a variety of reasons, with one potential culprit being electronic noise interference. Such interference could be caused by the high voltage difference between the PLC control (24VDC) and the Maxon valves (110VAC). The noise could then disrupt the PLC and consequently corrupt data. To isolate and assess this issue, you could try shielding your wires or use separate conduits for low and high voltage lines, thus minimizing the chances of interference. Take a look also at your control hardware and PLC power supply to see if they're functioning correctly. Lastly, if you haven't done so yet, closely analyze the system's behavior during the safety routine execution sequence; specifically, right before it goes to STOP mode. I imagine you've probably already done that but it's worth mentioning in case it was overlooked.
It sounds like you're dealing with a pesky intermittent issue there. Since the valves are 110VAC and your PLC operates on 24VDC, have you checked for any electrical noise or grounding problems that could be causing the data corruption? Sometimes, the voltage differences in control systems can lead to unexpected behavior or interference, especially if the wiring isn't isolated properly. Also, examining the communication between the PLC and the F I/Ologics may reveal some clues—maybe introducing some filtering or shielding could help stabilize the signals. It’s great that your OEM is involved, but perhaps collaborating with an expert who specializes in safety system diagnostics might yield fresh insights!
It sounds like you're dealing with a frustrating issue, especially since it seems to happen sporadically. Given the data corruption in the safety program, it might be worth looking into potential electrical noise or interference that could be affecting the 110VAC Maxon valves, especially since they're quite a distance from the 24VDC control signals. Have you considered adding any additional filtering or shielded cabling to help mitigate those interferences? Also, it might be helpful to check the grounding integrity in your system; sometimes a poor ground can cause odd behaviors like what you're experiencing. I hope you find a solid solution soon!
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Answer: Answer: The issue could be related to data corruption in the safety program as indicated by the diagnostic fault buffer, leading to the PLC entering STOP mode. The inconsistent triggering of the issue by different valves suggests a potential underlying problem within the safety blocks or communication between the PLC and the Maxon valves.
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