Automation Knowledged Base
An Introduction to Allen Bradley PLCs and the Evolution of Rockwell Automation PACs
Allen-Bradley is the brand name of several product lines of factory automation equipment and today its owned by Rockwell Automation. The company was founded by Lynde Bradley in 1903 with the financial support backing of investor Dr. Stanton Allen, the company eventually became the Allen-Bradley Company. Today, the company manufactures programmable logic controllers (PLCs), human-machine interfaces, sensors, safety components and systems, software, drives and drive systems, contactors, and motor control centers. Their first patented product was a carbon disc compression-type motor controller used for industrial cranes and the crane controller was exhibited at the St. Louis World’s Fair in 1904. Allen-Bradley became involved with programmable logic controllers by the inventor, Odo Josef Struger. He is often referred to as the father of the programmable logic controller. Allen-Bradley became a major PLC manufacturer in the United States during his employment with AB. He also contributed as a leader in the development of IEC 61131-3 PLC programming language standards.
The first Allen-Bradley PLC introduced to the market was the PLC-5 product family. The PLC-2 and PLC-3 were released in the 1980s and are now obsolete. The PLC-5 family used the 6200 series programing software originally and then later RSLogix 5 programming software. In 1991 the SLC500 product line was released. This platform was much smaller in size and had a reduced instruction set.
SLC was an acronym for Small Logic Controller and the first SLC500 released was an integrated package (commonly referred to as a shoe block PLC) containing the CPU, power supply, and IO.
The Micrologix family and SLC 500 PLCs used the RSLogix 500 programming software.
In 2014, the MicroLogix family was introduced in response to address the need for a less expensive PLC solution to compete with other manufactures and the first MicroLogix introduced was MicroLogix 1000 supporting several types of IO combinations. The platform did not use a rack but instead, modules were connected at the end of the package.
The ControlLogix family was introduced in 1997. This platform was racked-based having much faster scan times (speed) and memory than the PLC-5 or SLC products.
Communication modules supported Ethernet, DeviceNet, DH485, and ControlNet. Servo motor control cards using SERCOS fiber-optics provided competitiveness in the coordinated system servo market.
The CompactLogix family was released in 2008 as a lower-cost solution to ControlLogix for competitive reasons. And like the MicroLogix, the products do not use a rack-based solution but instead, use add-on modules to the ends of the power supply or CPU modules. Communications between the RSLogix programming and configuration software and PLC/PAC is handled using Rslinx software, a separate software package, that also supports DDE and OPC support.
PLC Basics | Programmable Logic Controller
The programmable logic controller, or PLC, is a special purpose computer. It has no display, no keyboard, no printer, no hard drive, and hides in the control panel out on the factory floor, but it is still a computer. Initially, the PLC was a replacement for panels of relays, devices that turn on and off. Making a machine run using relays as logic was time-consuming and challenging, and making a change in the logic or the operation of the machine was almost as complicated as starting over.