This is my first time working on a Siemens system, so I may not be familiar with all the terminology. While we have a colleague who works on Siemens systems, they are not experienced with older models like this one. I was called to investigate an issue with a PLC that has been in operation since 2008 but started experiencing faults and errors after being restarted following a winter shutdown. The PLC controls 6 tanks with valves and sensors connected to IM 151 modules in a series. The controller is showing SF and BF fault lights, with the first tank's IM 151 module functioning correctly while tanks 2 to 6 are showing SF/BF faults on the communication and power modules. Despite efforts to troubleshoot by checking cables and replacing modules, the issue persists. Although I was able to explore the program briefly, I could not access deeper settings due to a lack of a Step 7 license. The fault codes seem to be related to OB122 programming blocks. I have gathered diagnostic files and screenshots on an old computer with TIA 15, but I am unable to access them at the moment. If anyone has any insights or advice to help us resolve this issue, it would be greatly appreciated. I will gather additional information to provide a better understanding of the situation. Thank you!
Are there numerous dip switches located on the front of the IM151 module? If so, were they configured to match the settings of the previous module during replacement?
It seems like there may be a problem with either the profibus or IM at tank2. Have you tried activating the terminating resistor at tank2? If the IM151 was replaced at tank2, make sure the address was configured correctly. In the past, it was common practice to use address 1 for the CPU, 2 for a laptop or PC, 3 for the first remote rack, and so on. Some users would reserve addresses 2 and 3, and start assigning addresses from 4 onwards. Remember, when changing the address, you need to power cycle the system for the new address to take effect as the switches are only read during start up.
Inquiring about the IM151 module, dwoodlock asked if it has multiple dip switches on the front and if they were set correctly when replaced. Ken Moore suggested checking the terminating resistor at tank2 and ensuring the IM151 address was set properly. He also mentioned common addressing practices for remote racks. The IM151 was indeed replaced with the address matching the drawings. Each tank is addressed in increments of 10. Despite power cycling, difficulty in accessing the CPU was encountered until a power cycle was performed. Due to unfamiliarity with Siemens software, accessing it correctly was a challenge, especially without the Step 7 License to view the programming.
To ensure optimal performance, a termination resistor is crucial at the end of a Profibus daisy chain. Placing the resistor at Tank 2 effectively isolates the issue within the chain. If Tank 2 successfully operates, it indicates that any potential problem lies downstream. This troubleshooting method is essential for identifying and resolving communication issues on a Profibus network.
Ken Moore explained that in a Profibus network, it is essential to have a termination resistor at the end of the daisy chain. Placing the resistor at Tank 2 allows you to isolate the chain and identify any issues further downstream. Could the Off/On switches near the dip switches for addressing be causing the problem? While we have confirmed that Tank 1 is functioning correctly, we have noticed issues beyond that point. Our focus has primarily been on Tank 2, but could there be issues with Tanks 3, 4, 5, or 6 that are affecting the communication? We have reached out to Siemens tech support, who advised that we need STEP 7 software to properly configure the modules. This limitation in software access hinders our ability to troubleshoot potential issues such as faulty modules. Additionally, they mentioned the importance of having a terminating cap on the bus, which may have been overlooked by the electrician during the equipment swap.
It sounds like you're deep in the trenches with a tricky issue! Since the faults are occurring on the communication and power modules for tanks 2 to 6, it might be worth checking the power supply to those modules—it could be a voltage drop or even a grounding issue after the winter shutdown. Also, if you haven’t already, try resetting those modules to see if that clears the errors. If OB122 is involved, it's usually tied to hardware failures or communication problems, so verifying the communication pathways between the PLC and the IM 151 modules could provide more clues. Keep us posted as you gather more information!
It sounds like you're dealing with quite a challenging situation! Given the age of the equipment, it's possible that there could be hardware issues cropping up that aren't immediately obvious, especially after a long shutdown. Have you tried resetting the modules or checking for physical signs of wear or corrosion in the connectors? Also, since you mentioned OB122, those faults are often tied to communication issues — have you looked into the network configuration? Double-checking the connections and confirming that all modules are powered properly can sometimes make a big difference. If you can, getting your hands on a copy of Step 7 for full access to the program might unlock more details that could help you diagnose the problem further. Good luck!
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Answer: Answer: The SF and BF fault lights could indicate issues with the communication and power modules of the PLC, potentially leading to faults in the system.
Answer: Answer: Troubleshooting steps may involve checking cables, replacing modules, examining program settings, and investigating potential OB122 programming block-related issues.
Answer: Answer: To access diagnostic files and screenshots for analysis without a Step 7 license, you may need to find alternative methods or seek assistance from someone with the necessary access privileges.
Answer: Answer: To address faults and errors in a Siemens PLC after a shutdown, thorough troubleshooting, including checking connections, examining program settings, and potentially seeking expert advice, may be necessary.
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