1. To control a conveyor system

2. For simple designs

3. A PLC is a computer based controller that uses inputs to monitor a process, and uses outputs to control a process using a program.

4. Less expensive for complex processes, debugging tools, reliable, flexible, easy to expand, etc.

5. A PLC could replace a few relays. In this case the relays might be easier to install and less expensive. To control a more complex system the controller might need timing, counting and other mathematical calculations. In this case a PLC would be a better choice.

6. The ladder logic outputs were modelled on relay logic diagrams. The output in a relay ladder diagram is a relay coil that switches a set of output contacts.

7. off, on

8. Generic: LD A, LD B, OR, ST Y, END; Allen Bradley: SOR, BST, XIO A, NXB, XIO B, BND, OTE Y, EOR, END