The PLC configuration refers to the components physical organization. Typical configurations are listed below from smallest to largest.
1. Software - A software PLC based needs a general purpose computer with an interface card. The software uses the computer operating system resources to recognize control, logic and I/O functions. A benefit of such a configuration is that it permits the PLC to be linked to sensors, other identical PLCs or to other computers across a common purpose network, for instance the Ethernet. The PLC can also function along with other PC-based applications like visualization software.
2. Micro - These devices can be as small as a cards deck which suitable for table top or wall mounted. They likely to have permanent quantities of I/O and limited abilities.
3. Compact - A compact, all-in-one device that has limited development capabilities.
4. Mini - These are identical in function to PLC racks. These usually are situated completely at one place and do not use an expanded bus.
5. Rack - A rack is frequently large and can handle multiple cards. These cards, which recognize the special function modules, CPU, power, communication, and I/O are linked through a bus, called a backplane. Multiple racks can be associated together using bus extenders. Every channel in a card can be located by a scheme of channel addressing, which differs from vendor to vendor. These likely to be of highest cost, but also the more flexible and easier to maintain. The numerous functional subsystems types, that may or may not be the similar board, connected throughout a backplane. Nevertheless this does not reflect the various modules that build a PLC system. Distributed at a quantity of racks all along by bus expansion system that while direct correlation may be potential for expansion over small distances of a few meters.