Hello everyone, our 1768 CompactLogix 5345S safety controller with firmware version 20.14 is experiencing random major and minor faults. The minor fault is related to a math overflow, while the major fault occurs in our safety routine with a timeout error. I am wondering if the math overflow fault could be causing the major safety fault, as I believe it should trigger a processor fault. I would appreciate your thoughts on this matter. The machine operates 24/7, making it difficult for me to troubleshoot the issue as it is critical and I am not given enough time to investigate. They reset it while I am examining the logic so they can continue running it. Thank you in advance for your input, James.
No, a minor fault will not cause the PLC to stop functioning. Many PLCs experience frequent minor faults, often due to math overflow, but continue to operate without issue. For example, I observed a 1768 Compact Logix generating 10 minor faults per second while still running smoothly. In situations like this, the math overflow can be disregarded. Instead, focus on identifying the error code and exact error message of any major faults. It would be helpful to capture a screenshot of the major fault before resetting it for easier diagnosis.
James Mcquade is seeking advice on a recurring issue with a 1768 CompactLogix 5345s safety controller, which is experiencing both major and minor faults. The minor fault is attributed to a math overflow, while the major fault relates to a timeout error in the safety routine. Mcquade wonders if the math overflow fault could be connected to the major safety fault, as it technically should trigger a processor fault. However, due to the critical nature of the machine and limited access for investigation, he has been unable to pinpoint the root cause. Any insights or opinions on this matter would be greatly appreciated. In similar cases, a minor math fault like an overflow could potentially cascade into a watchdog timeout issue, particularly if there are issues within the code execution flow.
It is indeed a valid point that I overlooked. However, in the scenario where loops are utilized within a safety protocol, my proposed solution would involve initiating a blowtorch. This approach is vital for ensuring utmost protection and security in high-risk situations.
Thank you for the responses. The issue you are explaining is precisely what I am observing. It appears that a division by zero is causing a mathematical fault, along with a safety routine that is reaching a timeout. - James
I have a query about a control cabinet in a large plant that is experiencing frequent faults. The main culprit is identified as data overflow in an array index, causing a repetitive fault code. I suspect these faults may be causing issues with the primary network module, leading to intermittent loss of communication with a cloud service. Despite ongoing operations, these faults have resulted in significant downtime multiple times over the past few months. I plan to address the logic issue causing the faults, but I am also considering the possibility of the network module being at fault. Before making any decisions, I will monitor the situation to determine the root cause. IT has already confirmed the network infrastructure is not the issue.
Hey James, it does indeed sound like a tricky situation you're dealing with. While not impossible, it's relatively unlikely that a minor math overflow fault can cause a major safety fault directly. They typically affect different aspects of the system. The timeout error in your safety routine, however, may be suggesting some issue elsewhere. As you're finding it hard to troubleshoot with the machine running continuously, I would suggest trying to replicate the problem on a similar but non-operational unit if you have one available. This would allow you to investigate without any operational disruption. Alternatively, consider conducting troubleshooting during a low-production period if possible.
Hi James, from my experience with CompactLogix controllers, major and minor faults may not necessarily be linked. In your case, the math overflow minor fault could be due to some arithmetic computations in your program exceeding the controller's limit. On the other hand, the safety routine major fault possibly stems from an error within your safety code, specifically in regards to the allotted reaction time of your safety components. These could just be two concurrent faults and trying to pin the cause all on the math overflow might lead you down a rabbit hole. I'd suggest breaking down the issues separately and addressing each fault independently, considering your tight timeframe. Also, see if you can set aside a dedicated troubleshooting window - perhaps post-production hours - where the machine can be thoroughly reviewed without interruption. Good luck!
Hey James, it could be possible that the math overflow fault is indirectly causing the major safety fault. Your CompactLogix 5345S should trigger a processor fault with a math overflow. If it doesn't, there could likely be an issue with your error handling which might cause unexpected results, such as your safety routine timing out incorrectly. I would suggest isolating the instruction causing the overflow and fixing that first, then see if your major fault persists. It's also worth checking if there's a firmware update addressing this issue. And I hear you on not getting enough time to properly troubleshoot, sadly a familiar story in many industries!
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Answer: Answer: The minor fault is related to a math overflow, while the major fault occurs in the safety routine with a timeout error.
Answer: Answer: The interrelation between the math overflow fault and the major safety fault in the controller is a valid concern, as the math overflow fault should trigger a processor fault.
Answer: Answer: It can be challenging to troubleshoot these faults in a machine that operates 24/7. It's recommended to set aside dedicated time for investigation without interruptions to diagnose and resolve the issue thoroughly.
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