Simatic S5-155U BASPA low signal

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Hi everyone,

I am encountering some problems with a Simatic S5 system comprised of CPU 946/947, CP525, CP 527 and Analog/Digital I/O cards. The BASPA low voltage signal is being triggered randomly causing the CPU to suspend RUN Mode ( RUN Led goes Off and BASP Led goes On) and then go back to RUN resuming operation without ever going to Stop Mode. It's annoying. I found it was the BASPA signal because I programmed the Central Rack Power supply to trigger the fault Relay in case of a Low Voltage fault. I thought the BASPA low signal was output only by the Power supply (6ES5955-3LF12) but I read somewhere that BASPA low signal is also output by the CPU. I changed the CPU 946/947 for new ones but the problem persists. My question is: Who triggers the BASPA low signal? Is it the power supplies (in both Central & Expansion Racks) or the CPs or some other module?

Help will be appreciated,



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