How to solve the READ_NUA_DDT Function Block that stops updating the BMENUA0100 status variable after a swap over from Primary to Standby on a M580 redundant system

Issue :

The READ_NUA_DDT function block stops updating the value of the T_BMENUA0100 variable in a M580 hot standby/redundant system when swapping the Primary and Standby role of the 2 CPUs.

Product Line :

Control Expert

M580 hotstandby

BMENUA0100

Cause :

This is caused by the fact that the data of the management table of the READ_DDT block found inside the READ_NUA_DDT dfb is part of the data that is exchanged between both CPU. This might cause this block to stop operating when a swap occurs. It is explained in the help file of the block

Resolution :

To fix this, we need to disable the Exchange on STBY option for the instances of the READ_NUA_DDT blocks like shown below :

Released for: Schneider Electric USA