Understanding PLC Hardware and Wiring

Industrial automation has been in existence since before the programmable logic controller (PLC) was developed in the late 1960s. Relays and timers were used for automating manufacturing processes prior to the introduction of PLCs but they had so many challenges. Some of these challenges included the large space occupied by relays and timers, the amount of time required to troubleshoot the system, and making changes to the system was very difficult due to the fact that so many relays were hardwired together in a specific order for the machine to operate. A PLC provides a solution to all these challenges by needing less space, being easy to troubleshoot, and changes can easily be made to a control system that uses a PLC. The following photograph shows a relay room with so many relays that take up much space, are not easy to troubleshoot, and changes are not easy to make on the control system:

Figure 7.1 – Relays...