The replacement with a standard programmable logic controller (PLC) of original machine drive system masters that were built with customized computer hardware and firmware difficult to enhance and maintain only twelve years after their introduction is discussed. The reasons for master upgrades, a number of alternate hardware and software solutions for upgrading the original master with a PLC, compatibility of functions of the new PLC master, and master controller communications with drives and operator stations are presented. It is shown that the open architecture of PLCs promises to increase drive options in the future. The framework of the discussion is a project in which a PLC replaced an early design of a digital paper machine drive master.
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