Overview Of The Evolution Of Programmable Logic Controllers (PLCs)

The Evolution Manufacturing

The creation of any product requires a sequence of operations. In the old days, the sequence was done by human hands and simple tools. With the industrial revolutions, machines were invented to help reduce the need for manual labor and increase product quality. As time went on and the number of machines multiplied, creation of products was done more and more by a sequence of machines. Once products could be created by a series of machines, with minimal human intervention, it was a matter of time before manufacturers sought to speed up the process by electronically coordinating machines.

 The Birth Of Control Automation

In 1968 the automatic transmission division of General Motors sought to replace hard wired relay systems and control panels with a software based control system. GM was using thousands of relays, cam timers, drum sequencers and dedicated closed loop controllers. Whenever engineers wanted to update the manufacturing process, usually once a year, they had to rewire the relays and components consuming a lot of time and money. GM sought a system that could change the logic rather than rewiring relays.

Dick Morley of Bedford Associates, Bedford, Massachusetts, now known as the “father of the PLC”, designed the Modular Digital Controller or “Modicon” which used “ladder logic” and replaced relay logic with schematic diagrams, in the process reducing wiring by 80 percent. The computer based Modicon and models that came after it were designed to perform well in a shop environment, use discrete bit-from input and output, be easily learnable and allow operations to be monitored.

In the 1970s, the Modbus became the first industrial communications network based on Master/Slave architecture with messaging between Modbus nodes. Since then PLCs have been an integral part of factory and industrial process control and monitoring and are used in a wide variety of industrial machines, movable components and systems.

How PLC’s Work

Modern PLCs process binary inputs and outputs connected with logic statements. Inputs from limit switches or push buttons that indicate temperature, pressure, humidity etc., trigger outputs that activate equipment such as solenoids, valves, motors, etc. The “logic function” checks inputs, performs “logical functions” and generates an output. All of this takes place as part of programmed sequences and cycle which recurs as quickly as a process dictates.

The main areas of knowledge required to use PLCs most effectively include PLC theory, installation, programming, operation, and troubleshooting. The need for safe and efficient automation requires electricians, technicians, operators and supervisors to thoroughly understand PLCs. Since the 1970s, the technology has gone through a number of stages and advances.

Recent PLC Advances

In the 1980s General Electric created the Manufacturing Automation Protocol (MAP) to standardize connections amongst many PLC manufacturers. With the growing popularity of the personal computer (PC), dedicated programming terminals and handheld devices came into use. However, the operating systems in computers were less stable than operating systems in PLCs and not designed to tolerate temperature, humidity, and vibration needed in a manufacturing environment.

In the 1990s the IEC 1131-3 was introduced to create international standards for PLC programming languages. Progress was also seen in computer hardware and software allowing engineers to program and troubleshoot PLCs more quickly and effectively.

PLCs Today

Today PLCs consume much less energy, have self-diagnostic functions that speed up troubleshooting, contain significantly more versatile and easy to use software, contain fewer parts, operate in milliseconds drastically improving machine cycle time, cost less, are more reliable and can be installed quickly.

Finally, PLCs are now built in rugged enclosures and are protected from dust, dirt, moisture, and electromagnetic interference while operating at temperatures from 0° to 140° (60°C) and a humidity range of 0 to 90 percent.

Tags: Dick Morley, history, PLCs

This entry was posted on June 10th, 2014 and is filed under General, Technology. Both comments and pings are currently closed.