Hello to all the intelligent and knowledgeable individuals out there. I am currently facing an issue with my HMI connected to 2 PLCs via ethernet. These PLCs are controlling 2 systems within a single machine. The problem arises when the sensor readings on the HMI start freezing intermittently. Restarting the PLC resolves the issue temporarily. The PLC in question is connected to 3 sensors (4-20mA), and the readings from these sensors become abnormal during the freezing issue. I suspect the issue may be related to the AI card (1769-IF41) in the PLC. Additionally, the button programmed on the HMI to start the system also fails to function. This leads me to believe that the problematic PLC is not receiving feedback from the HMI. I would greatly appreciate insights from your collective experience in identifying the root cause of this issue. Thank you.
Insufficient isolation could result in issues with 4-20mA sensors.
Syahmi Noordin asked for help from experienced individuals in the field. He suggested connecting to the PLC's to investigate issues with freezing and recommended rebooting them to potentially resolve errors in the program. He also advised trying to disconnect sensors one by one during a freeze and checking for errors online. Additionally, he inquired whether the system is new or if the freezing issue recently began.
I'd recommend checking a few things to isolate the problem. Firstly, check the watchdog timer on your HMI. A more frequent reset might prevent the HMI from freezing. Secondly, check the communication latency between the HMI and the PLCs. Long communication lag times can cause the HMI to freeze while waiting for PLC feedback. You could also look into the PLC failure mode. Verify if it's entering the fail-safe mode, which might be the cause of your sensors reading abnormally. Finally, make sure your HMI and PLC software are updated, as the HMI may freeze due to a software-related issue. Please share any other error codes or symptoms you observe, as they could offer additional clues.
It does sound like a communication issue between your PLC and HMI. The problem may lie in the AI card as you suspect, but don't rule out other possibilities. The issue could also be due to a problem with your ethernet communication settings on your PLC or HMI. Check your timing and NPCI settings first. Another possibility could be an issue with the power supply to your sensors. If the power supply is unstable or insufficient, it might cause abnormal readings and intermittent freezing. Lastly, consider the possibility of a memory issue. If your PLC is close to its processing or memory limit, it might struggle to maintain steady communication with the HMI. Hopefully, one of these suggestions will lead you to the root cause. Good luck!
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Answer: - The freezing issue may be related to a potential problem with the AI card (1769-IF41) in one of the PLCs, causing abnormal readings from the connected sensors.
Answer: - Restarting the problematic PLC has been mentioned as a temporary solution to resolve the intermittent freezing issue with the sensor readings on the HMI.
Answer: - The failure of the button programmed on the HMI to start the system could be due to the problematic PLC not receiving feedback from the HMI, indicating a potential communication issue between the PLC and the HMI.
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