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Troubleshooting Major and Minor Faults in CompactLogix 5345S Safety Controller

Question:

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.

Top Replies

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.

More Replies

While minor faults may not initially seem like the cause, it would not be surprising if they were indeed playing a role in the issue. It's also important to consider the impact of network cabling. In one instance, a PLC was responding to pings but unable to connect with Logix 5000 despite various troubleshooting attempts. Even though the cable appeared to be in working order, after realizing it was the culprit, a simple patch cable replacement solved the problem. It's always worth thoroughly checking all aspects before reaching a final conclusion.

Ensure to review the safety task watchdog settings to avoid potential issues. In most cases, safety code is straightforward, as it should be. If the watchdog is properly configured, inspect the safety code for any potential pitfalls, such as non-terminating loops or lengthy execution times. If a timeout error occurs, it is likely due to one of these issues.

Frequently Asked Questions (FAQ)

FAQ: 1. What could be causing the random major and minor faults in the CompactLogix 5345S safety controller?

Answer: Answer: The minor fault is related to a math overflow, while the major fault occurs in the safety routine with a timeout error.

FAQ: 2. Is it possible that the math overflow fault is causing the major safety fault in the CompactLogix 5345S safety controller?

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.

FAQ: 3. How can I troubleshoot the major and minor faults in the CompactLogix 5345S safety controller effectively?

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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