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Power up or power failure indicator bit


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Hi, we have a Vision series V120, and we need to detect a power failure or power up condition to take different actions upon power up and based on where the PLC was at the time the power failed.


What functions or features does the software support for this type of use case? Are there any examples we can look at on how to handle this in the code?


Thank you,

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  • MVP 2023

I normally detect and log power off and power on conditions in the software I write. I do this by storing the date and time in an MI vector on every PLC cycle. On power up, I use the SB2 bit to prevent storing the Date and time to the MI vector prior to logging the power off condition. This provides the last date and time stored, which was at power off. Then, I log the power on date and time, also using SB2. From that you can determine anything you need, such as the length of time the PLC was powered off.


Regarding where the PLC was in the program loop at the time of power loss, operands retain their value through a power loss if the battery is installed and working. If there are critical intermediate steps, you can keep track of them with operands that will tell you where you are.

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