PLCs were initially introduced in the late 1960s. The main reason for the design of such a device was to eliminate the high cost involved in the replacement of the complicated machine control systems that were relay based. Bedford Associates proposed something known as Modicon, which stand for a Modular Digital Controller to a major United States car manufacturer. At the time, other companies proposed computer based schemes, and one of them was based on the PDP-8. The first PLC in the world was brought into commercial production by the Modicon 084.
When production requirements underwent change, the same case applied to the control system. Such frequent change turned out to be quite expensive. Since relays are mechanical devices, they have a limited shelf life that requires a strict maintenance program to be followed. Trouble shooting was also proving to be tedious due to the large number of relays involved.
Consider a machine control panel that has hundreds or probably thousands of relays. A size of that magnitude can be overwhelming due to the complex working of numerous individual devices. Such relays would have to be connected individually together using wires in a way that facilitates the achievement of a certain desired outcomes. During that particular time, so many problems had to be solved.
These modern controllers also had to be programmed easily by plant and maintenance engineers. The programming changes had to be easily performed and the lifetime prolonged. In addition, they had to survive the seemingly harsh industrial environmental conditions. The answers to these problems lay in using a programmed technique that most people were already familiar with as well as the replacement of mechanical parts with ones in solid state.
The PLC technologies that dominated the mid-1970s were sequencer state machines and CPUs that were bit slice based. In Modicon and AB PLCs, the AMD 2901 and 2903 were very popular. Convectional microprocessors lacked the power capable of solving PLC logic rapidly in all PLC except the smallest ones. As a revolution of these microprocessors took place, bigger PLCs based on them were being manufactured. Even nowadays some are still being made based on 2903. Modicon has not yet constructed a quicker PLC than the 2901-based one known as 984A/B/X.
Communication abilities started appearing in around 1973. The earliest of such a system happened to be Modicons Modbus. Communication between one PLC and others was now possible, and they could control a machine without being attached to it. Additionally, PLCs could send and receive voltages of varying magnitude to facilitate their introduction to the analogue world. The unfortunate thing was that rapid changes in technology and failure to achieve standardization reduced communications between PLCs to just physical networks and protocols that are incompatible.
The 1980s General Motors coming up with MAP (manufacturing automation protocol) in an attempt at standardizing communications. It was also the ideal time to reduce the PLC size and making them programmable to software through symbolic programming on PCs as opposed to handheld programmers or dedicated programming terminals.
The 1990s has seen the introduction of modern protocol as well as the modernization of protocols that were popular and salvaged from the 1980s. The firm that originally introduced the Modicon 084 went ahead and switched to a personal computer based control system.
When production requirements underwent change, the same case applied to the control system. Such frequent change turned out to be quite expensive. Since relays are mechanical devices, they have a limited shelf life that requires a strict maintenance program to be followed. Trouble shooting was also proving to be tedious due to the large number of relays involved.
Consider a machine control panel that has hundreds or probably thousands of relays. A size of that magnitude can be overwhelming due to the complex working of numerous individual devices. Such relays would have to be connected individually together using wires in a way that facilitates the achievement of a certain desired outcomes. During that particular time, so many problems had to be solved.
These modern controllers also had to be programmed easily by plant and maintenance engineers. The programming changes had to be easily performed and the lifetime prolonged. In addition, they had to survive the seemingly harsh industrial environmental conditions. The answers to these problems lay in using a programmed technique that most people were already familiar with as well as the replacement of mechanical parts with ones in solid state.
The PLC technologies that dominated the mid-1970s were sequencer state machines and CPUs that were bit slice based. In Modicon and AB PLCs, the AMD 2901 and 2903 were very popular. Convectional microprocessors lacked the power capable of solving PLC logic rapidly in all PLC except the smallest ones. As a revolution of these microprocessors took place, bigger PLCs based on them were being manufactured. Even nowadays some are still being made based on 2903. Modicon has not yet constructed a quicker PLC than the 2901-based one known as 984A/B/X.
Communication abilities started appearing in around 1973. The earliest of such a system happened to be Modicons Modbus. Communication between one PLC and others was now possible, and they could control a machine without being attached to it. Additionally, PLCs could send and receive voltages of varying magnitude to facilitate their introduction to the analogue world. The unfortunate thing was that rapid changes in technology and failure to achieve standardization reduced communications between PLCs to just physical networks and protocols that are incompatible.
The 1980s General Motors coming up with MAP (manufacturing automation protocol) in an attempt at standardizing communications. It was also the ideal time to reduce the PLC size and making them programmable to software through symbolic programming on PCs as opposed to handheld programmers or dedicated programming terminals.
The 1990s has seen the introduction of modern protocol as well as the modernization of protocols that were popular and salvaged from the 1980s. The firm that originally introduced the Modicon 084 went ahead and switched to a personal computer based control system.
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