History of Programmable Logic Controller (PLC)

The PLC was first developed by Bedford Associates under the name Modular Digital Controller (Modicon) for the American automobile manufacturer General Motors Hydromantic Division.

1969

The PLC was first developed by Bedford Associates under the name Modular Digital Controller (Modicon) for the American automobile manufacturer General Motors Hydromantic Division. Allen-Bradley offered a control system called the PLC.

1970-1979

PLCs have been developed to have faster processing speeds according to the changes in the microprocessor and the ability to communicate data between PLCs. The first system is Modicon's Modbus which started using analog signal input/output.

1980-1989

There has been an effort to standardize PLC data communication. General Motors has created a protocol called the manufacturing automation protocol (MAP). As the size of PLCs has steadily decreased, software has been produced that can program PLCs in symbolic languages, allowing them to be programmed via a personal computer rather than via a handheld or programming terminal.

1990-Present

There has been an effort to standardize the language used in PLC programming using the IEC1131-3 standard so that PLCs can be programmed with

• IL (Instruction List)
• LD (Ladder Diagrams)
• FBD (Function Block Diagrams)
• SFC (Sequential Function Chart)
• ST (Structured Text)

Before the introduction of PLCs, microcontrollers had been in use for quite some time. However, when it comes to actual microcontroller use, almost everyone encounters problems. They don't know which commands to use to achieve the desired results. Whether using assembly language or a more advanced language like C, Pascal, or BASIC, the work is still complicated. Especially in industrial control, speed of use, editing, and verification are crucial. Given the difficulties of using these languages, the idea arose that there should be a language that's easy to use. This led to the creation of Ladder, a language that initially mimics a relay sequence circuit, resulting in a ladder diagram that follows the relay circuit diagram. The hardware is designed to be robust and resistant to various interference signals, and is a more user-friendly module called a PLC (Programmable Logic Controller). PLCs have been in use in Thailand for quite some time, initially installed on imported machinery. Over time, they've become increasingly popular due to their ease of use and ease of circuit modification, requiring minimal or sometimes no hardware modifications. Therefore, it is more suitable for practical use than microcontrollers

Compiled by Mr. Nu

refer : http://www.unseentronic.net/plcmanual/plc24n.htmhttp://www.star-circuit.com/article/PLC3.html