29-02-2016, 04:57 PM
The Need for PLCs
• Hardwired panels were very time consuming to wire, debug and change.
• GM identified the following requirements for computer controllers to replace hardwired panels.
- Solid-state not mechanical
- Easy to modify input and output devices
- Easily programmed and maintained by plant electricians
- Be able to function in an industrial environment
The First Programmable Logic Controllers (PLCs)
• Introduced in the late 1960’s
• Developed to offer the same functionality as the existing relay logic systems
• Programmable, reusable and reliable
- Could withstand a harsh industrial environment
- They had no hard drive, they had battery backup
- Could start in seconds
- Used Ladder Logic for programming
Programmable Logic Controller
• A programmable logic controller (PLC) is a specialized computer used to control machines and process.
• It uses a programmable memory to store instructions and specific functions that include On/Off control, timing, counting, sequencing, arithmetic, and data handling