· Many configurations and packages are available. But essential components are,
- power supply - Provides voltage/current to drive the electronics (often 5V, +/- 12V, +/- 24V)
- CPU - Where ladder logic is stored and processed, the main control is executed here.
- I/O (Input/Output) - A number of input/output terminals to connect to the actual system
- Indicator lights - Indicate mode/power and status. These are essential when diagnosing problems.
· Common Configurations
- Rack - A rack, or number of racks are used to put PLC cards into, these are easy to change, and expand.
- Shoebox - A compact, all-in-one unit (about the size of a shoebox) that has limited expansion capabilities. Lower cost, and compactness make these ideal for small applications.
