From the 1970s up until roughly the end of the century, centralized programmable logic controllers were the center of attention when it came to driving improvements in automation. Uniformity and repeatability were the name of the game. Back then, software and communication protocols were a common differentiator to measure the effectiveness of automation. The key benefits of these systems were to establish higher levels of uniformity and efficiency in the processes themselves.
Sensors were an integral part of these systems, but their role was limited compared to their role today. They basically communicated to their host PLC that something happened. For example, “The engine block is here. The hole is drilled. The drill is retracted.”