A Complete Introduction to Allen Bradley PLCs

This article will provide a complete background and overview of the Allen-Bradley automation product lines.

We have had a very positive response on our Allen-Bradley (AB) – Rockwell Automation article lessons with requests to produce more lessons on these Allen-Bradley PLC and PAC systems and associated programming.

PLC is an acronym for Programmable Logic Controller.

– PAC is an acronym for Programmable Automation Controller.

As you may know, PLCs have come a long way over the last 50 years with improved overall hardware and programming functionality, and so that in short describes the differences between a PLC and a PAC. PLCs have evolved into PACs.

Allen-Bradley PLCs over the last 50 years

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.

Allen-Bradley is the brand name of several product lines of factory automation equipment and today it’s owned by Rockwell Automation.

Allen-Bradley products

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.

Allen-Bradley Products

They are headquartered in Milwaukee, Wisconsin, and landmarks the AB Clock Tower having features with the largest four-sided clock in the western hemisphere

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.

AB Carbon Disc Compression-Type Motor Controller

Allen-Bradley PLC

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.

Odo contributed the ideas leading up to the invention of Allen‑Bradley PLCs over a period from 1958 to 1960 and is accredited with inventing the acronym PLC.

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.

There you have it, a bit of history for a great company.

PLC-2, PLC-3, PLC-5

Now let us talk about the product line that makes them so great.
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.

These PLCs were followed by the PLC-5 and is still in use today.

AB PLC-3 and PLC-2

The PLC-5 family used the 6200 series programing software originally and then later RSLogix 5 programming software.

SLC series

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 I/O.

Allen-Bradley SLC Series

Later the SLC5/01 was the first racked based SLC series released.

The 5/02 and 5/03 PLCs had DH485 (Data Highway serial-based communication) and the SLC5/04 provided a faster communication called DH+ (Data Highway Plus).

The SLC5/05 has both DH485 and Ethernet communications.

AB DH485 and DH+ Communication

Micrologix family

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 I/O combinations.

The platform did not use a rack but instead, modules were connected at the end of the package.

Allen-Bradley Micrologix

ControlLogix family

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.

Allen-Bradley ControlLogix Family

CompactLogix family

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.

Data mining and Analytics

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.

You can learn more about Rockwell Automation by attending the Rockwell Automation – Automation Fair held annually.

This concludes, An Introduction to Allen-Bradley PLCs and the evolution of the Rockwell Automation PACs.

Stay tuned for additional lessons about Rockwell Automation and Software related programming technique topics.

If you have any questions about the Allen-Bradley PLCs or PLCs in general feel free to add them in the comment section. We read each and every comment and reply to it in less than 24 hours.

Got a friend, client, or colleague who could use some of this information? Please share this article.

The RealPars Team
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