Last night at my workplace, we experienced a critical issue with a machine controlled by a SLC500. This machine, which is an oxidizer used to burn off solvent gases from printing presses, relies on a "common PLC" (Compactlogix) to receive an enable signal. The Compactlogix PLC receives inputs from the SLC500 through a serial to Ethernet adapter and then sends an "okay to start" signal to each press. However, a malfunctioning gas valve on the SLC500 caused it to shut down while the other machines continued to operate due to the outputs from the Compactlogix. It appears that the communication between the SLC500 and Compactlogix froze, resulting in the inputs being stuck in the ON position. After cycling the key on the Compactlogix PLC, the inputs from the SLC updated and turned off. Have you encountered a similar issue before? If so, what steps would you recommend taking? I have not been able to replicate the problem, and this system has been in place for several years.
Has anyone experienced a similar issue as described by Jmccoy? What steps would you recommend taking in such a situation? While I have not been able to replicate the issue before, it is important to look into the concept of a "handshake" in PLCs. This involves setting up a timer to pass information between PLCs, triggering an alarm if a response is not received within a set timeframe. This can be useful in detecting issues and potentially stopping processes if necessary.
I greatly appreciate your help, which has given me a fresh perspective on our system's issues. Our alarm for Communication loss was triggered a few weeks ago, but it went unnoticed as everything seemed to be functioning smoothly. Moving forward, I plan to incorporate this fault output into our system logic to prevent any similar incidents. Additionally, I am considering upgrading to a compactlogix processor as a precaution, given the recent Communication fault with the SLC system.
If issues persist, it is essential to meticulously craft the logic and ensure it is executed correctly. By doing so, you will be better equipped to pinpoint any underlying problems. Please keep us informed of your findings.
A user, geniusintraining, suggested not making any changes to the current logic and recommended re-evaluating it. They emphasized the importance of accurately writing the logic to diagnose any issues that may arise in the future. The user expressed gratitude for the assistance and planned to update the logic the following day to test for any failures. They promised to share any discoveries in the thread.
You are welcome.
Yes, I've seen a similar issue with an HVAC system we use that had A-B plc's in a similar setup. It sounds like a failure in the watchdog timer on the Compactlogix side, which in our case, caused the Compactlogix PLC to stop updating the inputs from the SLC even when they changed. It only restarted when we manually reset it. Your "stuck in ON position" sounds very familiar to this. We ended up setting a fail-safe in the code to force a reset of the Compactlogix PLC if there was ever a mismatch between the inputs from the SLC and the internal state of the Compactlogix. Might be worth a try for you, too!
It sounds like a complicated issue you've run into - I've experienced something similar in the past. It may be possible that the issue lies with the serial to Ethernet adapter, which can sometimes freeze due to communication constraints between the SLC500 and Compactlogix. Therefore, it could be beneficial to check the adapter or even substitute it with a new one to see if the issue persists. Also, consider routinely monitoring the statuses of the gas valve on the SLC500 to detect any early signs of malfunction. Last but not least, ensure the software of both, the SLC500 and Compactlogix are up-to-date. Sometimes, legacy software versions can cause unanticipated system glitches. If the problem continues, hiring a professional to conduct a thorough inspection might be the way to go.
I've experienced a similar situation with my system at work. It could be an issue with the serial to Ethernet adapter failing to communicate efficiently between the SLC500 and Compactlogix. Also, consider checking the code running on both PLCs. If there's an error in the code, it could cause a lag in communication. Another possible culprit could be the problematic gas valve. If it's sending false signals to the SLC500, that could bring about the system anomalies you described. If all else fails, it might be a good idea to reach out to a PLC specialist or the manufacturer - they usually have good troubleshooting resources. The issue is likely a combination of factors so take it step by step, it can be a tedious process but that’s often the nature of the work.
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Answer: The issue could stem from various factors such as a malfunctioning gas valve, a freeze in communication between the two PLCs, or a problem with the serial to Ethernet adapter.
Answer: To troubleshoot the issue, you can try power cycling both PLCs, checking the serial to Ethernet adapter, verifying the communication settings, and ensuring that the wiring connections are secure.
Answer: To prevent such issues, regularly inspect and maintain the equipment, monitor communication logs for any anomalies, conduct periodic testing of the system, and consider implementing redundancy or backup communication methods.
Answer: If the inputs are stuck, you can try cycling the key on the Compactlogix PLC to force an update of the inputs. Additionally, checking the programming logic and addressing any faults in the system may help resolve the issue.
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