In 1970, a fierce contest was being waged inside General Motors’ Hydra-Matic Transmission Division in Ypsilanti, Michigan. At stake was program ownership of what would become the first programmable logic controllers (PLCs), and the outcome would shape not only the design of the first PLCs, but also the success or failure of their advocates.

PLC incubator

It was natural that GM’s premier manufacturing technology group, Hydra-Matic, would be the incubator of the PLC. A nationally recognized technology leader, Hydra-Matic had installed one of the early IBM 1800 computers, the IBM 1801.

Richard Lundy, an owner of one of the original PLC suppliers, tells the story of when Ed O’Connell, a Computer Group engineer, didn’t think GM was getting enough support from IBM. "An entire test line was running off of the one computer," Lundy said, "which made it very vulnerable, and Ed didn’t like the support he was getting. So he called Watson." That’s Thomas Watson, Jr., the son of IBM’s founder and company CEO. Support for Hydra-Matic’s IBM system quickly improved.

Fuel: Hydra-Matic internal competition

In April of 1968, a young Hydra-Matic engineer, Dave Emmett, proposed the development of what he called a "Standard Machine Controller." The controller he envisioned would replace the relay systems that controlled machine operations. Emmett was in charge of the Circuitry Group, and he envisioned a machine that would reduce maintenance costs, improve machine diagnostics, and decrease panel space.

Randy Brodzik, who later worked for Emmett, remembers that Emmett had a clear vision of what was needed: "Dave said the goal was to develop a technology that would significantly reduce the time it took to make changes to a machine control sequence. With relays, first you had to do all the documentation, and then change all the wiring. It would take hours."

At about the same time, another group in Hydra-Matic was envisioning a different type of machine control system for GM. The Computer Division had hired Information Instruments, Inc. (3-I) to create a computer controlled assembly machine for the forward clutch line. This new control system had no limits to the number of elements in a ladder diagram, included parallel processing, and could incorporate complex Boolean equations.

Richard Lundy, a program manager for 3-I at the time, said the competition between the two Hydra-Matic Groups was "pretty dramatic." He described the Circuitry Group as wanting to duplicate existing ladder diagrams, while the Computer Group wanted to use nonsequential programming, similar to that used in current end-of-line test systems, to provide a more robust instruction set and reduce processing time. The advantages and limitations of each approach would become clear as the project progressed.

3 finalists, different architectures

In April and May of 1968, work was done on a request for proposal that is remarkably simple by today’s standards. The RFP, issued in June 1968, included only four pages of design specifications, including a requirement that "memory word length shall be at least eight bits." Douglas Brant worked on specifications for equipment coming into Hydra-Matic. He said that there was a strong rivalry between the Computer Group and the Circuitry Group in developing the specifications. "I guess it boiled down to people’s territory," Brant said.

Of the many companies who received the RFP, three were selected for evaluation: Digital Equipment Corporation (DEC), 3-I, and Bedford Associates, a consulting firm. Its products were the DEC PDP-14, the 3-I PDQ-II, and Bedford Associates’ Modicon 084. (The Modicon name came from MOdular DIgital CONtroller.)

In June of 1969, DEC’s PDP-14 was installed to control a gear grinder. Richard Lundy says that in spite of a very strong GM-DEC relationship, DEC’s concerns about memory failure significantly limited the PDP-14’s competitiveness. To make a change to the DEC program, "you had to send the client program in to them, and they would send you back a hardwired memory board," Lundy said. Having to remove a controller’s memory from the plant to make changes would prove to make the DEC option unsustainable.

2 Hydra-Matic Groups, alliances

Richard Lundy’s company, 3-I, was aligned with the Hydra-Matic Computer Group. Lundy said that during the evaluation period, the rivalry between the Computer Group and the Circuitry Group escalated. To the Computer Group, the advantages of higher level logic capabilities were clear and the selection of the PDQ-II was an obvious one. The 3-I solution for the forward clutch line, with its complex programming, had performed beautifully. Lundy said the PDQ-II quickly became known within the Computer Group as "pretty damn quick."

Emmett and the Circuitry Group advocated strongly for the Modicon 084. The programming that was seen as a benefit by the Computer Group was seen as a detriment by Emmett’s team. Because Modicon’s programming language was similar to the Group’s familiar relay ladder diagrams, it was expected to provide the smoothest transition and lowest cost for training and support. Randy Brodzik recalls that Emmett had an implementation view of the project: "He said that in order for this new technology to achieve wide acceptance, it needed to emulate what was already in place."

As an added bonus for Modicon, the 084 was the only controller built into a hardened package, providing plant floor protection that the other two options did not.

PLC design comparison

The three controllers were evaluated during the next two years and on June 3, 1970, the design considerations comparison document was finalized. As expected, the competition was intense among the vendors as well as their Hydra-Matic advocates.

Douglas Brant remembers that it wasn’t difficult to envision how lucrative the PLC would become.

"People felt it was doable, and all they needed to do was walk inside the factory and count the number of machines and they could start to come up with a number that looked like the national debt," Brant said.

The limitations that would ultimately undermine DEC’s PDP-14 show up under Hydra-Matic’s design requirements comparison. In the requirement to store memory data, the document said: "PDP-14 cannot because it has a read-only memory." DEC is also the only one of the three that would not provide a program listing of a wiring list. The comparison gives the advantage here to 3-I and Modicon: "Program listing of a wiring list speeds up installation and troubleshooting. Also reduces errors," the document said.

While DEC’s computing capabilities were strong, its approach of maintaining close control appears to have proved too restrictive and costly.

While all three companies placed their "Standard Machine Controllers" in industrial environments, Modicon and 3-I proved to have the most effective implementation. 3-I was purchased by Allen-Bradley in 1971, and Modicon’s programming language mimicking relay ladder diagrams is still used by PLC manufacturers today. Douglas Brant makes no effort to refute Modicon’s claim to inventing the PLC. "Their four element design was so similar to the ladder diagrams that were already in use, it just made sense that their product would win out overall."

Final product, a team effort

Within Hydra-Matic, Douglas Brant said he believes that it was the collaboration between Dave Emmett and Ed O’Connell that kept the project from becoming deadlocked: "Dave was always the kind of guy who could see the future, and he and Ed wanted what was best for Hydra-Matic." Randy Brodzik remembers that Ed and Dave "always looked for the best solutions for the company and the industry."

Richard Lundy stayed with 3-I through its acquisition by Allen-Bradley and later established Control-o-mation (later COM Inc.). He returned to Hydra-Matic in 1998 as a consultant for a test stand project. Dave Emmett left Hydra-Matic in 1980 and founded Superior Controls in nearby Plymouth, Michigan, which grew to become an engineering integration company, RedViking.

Randy Brodzik was with the GM Hydra-Matic Controls Group from 1983 to 1990 before leaving to join Dave Emmett at Superior Controls (now RedViking). Douglas Brant worked for Hydra-Matic for 18 years, until he also left to join Dave Emmett at Superior Controls (now RedViking). Ed O’Connell continued with GM Hydra-Matic until he retired, and Richard Lundy describes him as "a wonderful friend and mentor."

Rivalry is the foundation of many great inventions, and today’s PLCs are the result of productive competition at the U.S. manufacturer, GM’s Hydra-Matic Transmission Division. We’re still benefiting from the results.

– Randall Brodzik, president and CEO of RedViking, worked for Dave Emmett for 29 years, until Emmett passed away in 2007. Material here on the "Standard Machine Controller" project resulted from Brodzik’s conversations with Emmett, Control Engineering, and other historical articles. Edited by Mark T. Hoske, content manager, CFE Media, Control Engineering, mhoske@cfemedia.com.

ONLINE

This September 2014 article links to a 2008 Control Engineering article, "How Programmable Logic Controllers Emerged from Industry Needs," commemorating the 40th anniversary of the PLC, including information from Dick Morley, involved in the Modicon effort, who is sometimes called the "father of the PLC." Included there are tables and graphics on PLC development, including a list of five PLC manufacturers in 1970 and many more by 1975. Morley’s patent record for the first PLC called it a Small Scale Digital Computer. The patent itself says Digital Computer. Archive includes other history. See article linked below.

Key concepts

General Motors’ Hydra-Matic Transmission Division, an early user of computers on the plant floor, wanted something more reliable and flexible than computers or relays.

In April of 1968, a young Hydra-Matic engineer, Dave Emmett, proposed the development of what he called a "Standard Machine Controller."

Goal was to develop a technology that would significantly reduce the time it took to make changes to a machine control sequence.

Consider this

What old production issues could you resolve with a dose of new technology?

ONLINE extra

About the author: Randy Brodzik worked for Dave Emmett for 29 years, until Emmett passed away in 2007. Much of what Brodzik knows about the "Standard Machine Controller" project comes from conversations with Emmett. Today, Randy Brodzik serves as president and CEO of RedViking. In addition to personal conversations with Richard Lundy and Douglas Brant, Control Engineering sources and other historical documents provided information for this article. Although efforts were made to be as factual as possible, memories differ and errors occur. Corrections and comments are welcomed and can be directed to Mark Hoske, mhoske@cfemedia.com. Or add to the comment section below.