Allen Bradley PLCs

Rockwell Automation - Allen-Bradley PLC Product Development and Model/Series

Shortly after the death of co-founder Harry Bradley in July 1965, Allen-Bradley embarked on a journey that began with a challenge from General Motors to improve on the concept of standard computer control. This already existed, to a point, in the form of extremely large relay boxes - sometimes the size of entire rooms - that were designed to control another machine. By 1968, advancements in computing technology were bringing engineers ever closer to the possibility of making computer control a manageable, highly functional process.

Whether the future was wholly envisioned at this time, the ultimate goal would be a computer, or network of computers, that would make full industrial automation possible.

Pre-1970 - PDQ-II and PMC

A-B did not necessarily "win" the challenge brought by GM, but instead moved to purchase Bunker-Ramo Corporation, as well as Information Instruments, Inc., which had already developed the Program Data Quantizer, or PDQ-II controller. This model proved too big and too hard to program, even after several upgrades. But, Allen-Bradley persisted, and from the ashes of PDQ-II the programmable matrix controller arose.

1970 - PLC-1

The PMC was A-B's first functional controller; however, it still did not fully serve customer needs for machine controls. Improvements made based on these needs would result in the first A-B programmable logic controller, PLC-1, developed in part by Odo Struger, who also coined the now industry-wide acronym PLC.

Around this time, seven companies were in the PLC business, including contenders Allen-Bradley, Modicon, General Electric, Square D and Industrial Solid State Controls. And although PLCs were obviously a breakthrough that would revolutionize automation, they were still comparatively primitive. They were largely developed and used for specific applications, most often in the automotive industry.

But, Allen-Bradley was quick to implement improvements to its PLC and take advantage of the leaps in computing technology that were seemingly occurring by the hour. The company introduced its first computer interface and necessary offline software for PLCs by 1972, and followed that with the first PLC enabled with a CRT-based panel, to allow more efficient user programming.

In 1976, A-B famously introduced remote input/output systems, or Remote I/O, which would connect a PLC to devices, including operator interfaces, that are located elsewhere. This innovation would help reduce costs and increase efficiency when integrating and maintaining PLCs, and usher in the next generation.

1978 - PLC-2

The PLC-2 family is likely the oldest family of Allen-Bradley PLC still being used today. Parts are still available for these legacy controllers, and requests for software updates arise, if infrequently. Whatever innovation the model itself may have brought to the PLC market, however, was outshined a year later by A-B's introduction of the Data Highway - the industry's first plant floor network.

PLC-2s could bask in the reflected light, though, of being among the first PLCs to be connected via a Local Area Network (LAN) cable system, and provide peer-to-peer capabilities between PLC controllers and computers. This family was based on the Intel 8080 microprocessor, which supported 256 I/O ports, essentially turning a little power into a powerhouse for its time.

1981 - PLC-3

Increased demand in an integrated PLC framework required more processing power, and that's what the PLC-3 family delivered. This model was based on a significantly more advanced "bit-slice" AMD microprocessor, and offered the ability for multiple configurations and expansion options depending on the user's current needs vs. potential growth.

This was a time of great a varied development in the PLC community, but one problem that still remained was a lack of standardization across systems. These two movements were in conflict, and created a need for some kind of organization.

In 1985, A-B introduced an IBM-compatible programming terminal, and shortly after that it succeeded in linking controllers to personal computers, which ushered in the modern era of highly adaptable PLCs.

1986 - PLC-5

The PLC-5 is used all around the globe and marked a turning point in flexible PLC technology for A-B, despite its being bought out by Rockwell Automation in the year it was introduced.

Based on the Motorola 68000, this controller made a quantum leap in terms of processing power, as well as having the capability of forward compatibility - the ability to adapt to further evolutions of the PLC platform. This would prove essential as A-B fully embraced the imminent explosion of Internet utility in industrial automation, and communication in general.

There are more than 450,000 PLC-5 controllers being used worldwide in a wide array of industries, including wastewater treatment, automotive manufacture, metals production and all aspects of shipping. And, A-B has ensured a continued presence in these industries by designing controllers that have the network ability and flexible connectivity that enables them to work with the PLCs that would come next, as well as handle Internet-based applications.

1991 - SLC 500 System

The SLC 500 series was largely designed to answer one major question left by its predecessor - how to deliver industrial automation in a smaller package. Rockwell Automation estimates that more than 75% of companies that make up the Dow Jones Industrial Average use the SLC 500 System. This, along with a current global distribution that well exceeds the PLC-5 may easily make this Allen-Bradley's most widely used series.

In 1993 this series, along with the compatible PLC-5, fully entered the global communications community when A-B reached beyond LAN to introduce Ethernet and TCP/IP connectivity. This, along with the ability of using computer-based software to interface with PLCs allow for more software application integration, leading to enhanced debugging and scanning, which increases efficiency.

1994 - MicroLogix 1000

A-B experienced a burst of development in 1994, beginning with the launch of the MicroLogix family - a "micro-control" option that even further reduced the size of the standard PLC, while still offering an amazing amount of power and expansion options for growing industrial needs.

A-B also launched DeviceNet, an innovative "open-standard" communications protocol that A-B makes available to third parties and is managed by an independent company, which encourages A-B PLC use through increased compatibility. In tandem, A-B also introduced Flex I/O, which allows users increased input/output modules without the need for additional physical storage space. A-B then showcased ControlNet in 1995, in addition to shipping its one millionth PLC. ControlNet is a high-speed, high-performance open network option similar to DeviceNet that allows even more efficient PLC communication and interface capability.

Micrologix is available in the 1000, 1100, 1200, 1400 and 1500 models, with each offering more power, connectivity and expansion flexibility than the last.

2001-Present - Pico Controller

Development through the rest of the 1990s focused more on modernization or alternation of existing protocols, rather than creating new PLCs. An example of this is Allen-Bradley's latest and last PLC offering - a controller that is more of a relay. The Pico (Series A and B) is a stripped-down "PLC" that designed for simple cost-efficient control applications, such as parking lot lighting operation.

Along with the Pico, evolution continued in the A-B brand line during the early 2000s up until the current time with an expansion into a new version of the PLC, designated as a PAC, or programmable automation controller, which is aimed to emphasize a fuller integration between PLC and computer interface. The A-B line of PACs, including CompactLogix, ControlLogix, FlexLogix, SoftLogix and Drivelogix systems, offer a more user-friendly experience, and can reduce time spent on traditional logistical issues (operation, maintenance, etc.). But, in terms of their function, they still fall within the PLC family."

• CompactLogix System
• ControlLogix System
• FlexLogix System
• SoftLogix System
• Drivelogix System

It would appear that as the bigger needs were being met and exceeded by more powerful microprocessors, more connectivity, more I/Os and more flexible options, a back-to-basics approach seemed to be the only direction to go. Indeed, Rockwell Automation's slogan, "Welcome to the World of Complete Automation," would seem to suggest a dawn of perfection in the world of PLC development.

CompactLogix, ControlLogix, FlexLogix, SoftLogix and Drivelogix systems

Allen Bradley

Allen Bradley