Why do simultaneous fault alarms occur for the signals in the same AI card within three Siemens PLC control cabinets?
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This project is equipped with 3 boosters, each having its own PLC control cabinet. However, during operation, signal alarms from the same AI card inside the three PLC cabinets occur from time to time, resulting in the boosters tripping simultaneously； Upon inspection, it was found that there are 7 AI signals on this same AI card; only the motor current of the first channel is powered from an external source, with the current signal coming from a transmitter located in the electrical frequency conversion cabinet. All the other signals originate from transmitters powered by the PLC itself. It is suspected that the sudden change in this current signal caused the signal failure alarms across the entire card. But why did the same card in all three PLC cabinets trigger alarms for similar signal failures at the same time? Please ask an expert to help analyze it. Thank you! ! !
It is advisable to use an isolator for the signals from electrical sources. Is the AI card model 331-7KF02? Follow the diagram to properly ground it
Isolating all channels on these two AI cards with safety barriers makes it difficult to determine which channel is causing the failure of that AI card
The current signal from the inverter does not require an external power supply.
The \"dirty\" power supply provided by the inverter contaminates the electrical grid, which is why all three PLCs start giving error messages. Please, for heaven’s sake, stop using that crappy power supply provided by the inverter to power the instruments.
I have encountered similar problems; it is recommended that the original poster also check the signals of other modules. The problem I encountered last time was that a voltage signal from the AO module caused data loss on another AI card.
This post was last edited by hfrs on 2019-4-4 14:20. No power supply is required.
There is voltage at the inverter side, so no power supply is needed on the PLC side; an isolator is generally used for this purpose.