Reference : Siemens Basics of Plc
a PLC can do complex tasks, replacing wiring between devices and relays by PLC
program.Modifying the application and correcting errors are easier . program in
advantages of PLCs : -
• Smaller size.
• Easier and faster to make changes.
• PLCs have integrated diagnostics .
• Applications can be immediately reported.
• programs can be duplicated faster and less expensively.
Comparison of PLC with Other Control Systems
| Relay systems | Digital Logics | Computers | PLC systems | C\Cs |
| Fairly Low | Low | High | Low | Price Per Function |
| Bulky | Very Compact | Fairly Compact | Very Compact | Physical Size |
| Slow | Very Fast | Fairly Fast | Fast | Operating Speed |
| Excellent | Good | Fairly Good | Good | Noise Immunity |
| Time Consuming in Design and Install | Time Consuming in Design | Time Consuming in Programming | Easy in Programming and Install | Installation |
| None | Yes | Yes | Yes | Complex Operation |
| Very Difficult | Difficult | Quite Simple | Very Simple | Ease of Changes |
| Poor-large No. Of Contacts | Poor if ICs Soldered | Poor-several Custom Boards | Good-few Standard Cards | Easy of Maintenance |
