A brief history of Rockwell Automation
In 1901, while working for Milwaukee Electric, Lynde Bradley (a teenager at the time) devised a better way to build the controllers that regulate motor speed. He soon quit his job, secured a small $1,000 investment from his lifelong friend, Dr. Stanton Allen, and co-founded the Allen-Bradley company with his brother, Harry Bradley, in 1903. The primary focus of Allen-Bradley was,for several decades, motor controllers, until they received an unusual request from GM in 1968 to build a system to replace their hardwired relay logic with something more dynamic—a standard machine controller.
Program Data Quantizer II and the Programmable Matrix Controller
Allen-Bradley responded to GM's request with two solutions—first, a large, difficult-to-program, expensive minicomputer-based Program Data Quantizer (PDQ) II in 1970 and later, the smaller and easier-to-program Programmable Matrix Controller (PMC) in 1971. The PMC was an early precursor to the modern PLC, and Allen-Bradley later adopted the term PLC for future releases of their automation products.
Although Allen-Bradley did not win the GM bid, the PMC continued to evolve until the release of the PLC-2. GM awarded the contract to Dick Morley and his company, Bedford and Associates. Dick Morely spun off a new company, named Modicon, and started to sell a PLC product called the Modicon 084 (named because it was prototype #84) based on this initial design.
PLC-2 controllers
Allen-Bradley introduced their very first PLC (PLC-1) in 1970, and it continued to evolve until the release of the PLC-2 in 1978. The PLC-2 played a vital role in the Space Shuttle program as Rockwell International was a primary contractor. The PLC-2/20 and many other AB controls were used in the manufacturing and testing of the 153-foot one-time-use tank, which fueled and provided structure to the shuttle.
The PLC-2 family of processors featured three versions:
- PLC-2/10
- PLC-2/20
- PLC-2/30
The more-powerful PLC-2 processors ran on a 1772-LP3D4 processor running at 47 to 63 Hz and supporting up to 16 K (16 data bits) of memory capacity.
The following diagram depicts the original PLC-2/30 controller:
It is possible that a few PLC-2/30s or PLC-2/20s could still be found in the field today. The PLC-2 can be programmed using 32-bit operating systems, such as Windows 8. The PLC-2 can be programmed using the 6200 programming terminal or Application Interface (AI) programming version 6.24 and a serial interface. The Rockwell AI software is an MS-DOS-based programming interface that provides a text-based graphical interface for viewing and editing ladder logic.
In the next section, we will discuss the third PLC created by Allen-Bradley—the PLC-3.
PLC-3 controllers
The PLC-3 was introduced in 1981 (the same year that the first Space Shuttle launched) and provided significant scalability increase for control systems. The PLC-3 was usually packaged with a programming terminal, much like the PLC-2. The PLC-3 supported up to 128 K (16 data bits) of memory capacity.
The following diagram depicts the Allen-Bradley PLC-3 controller unit, which featured a numeric keypad for programming and adjustments:
In the following section, we will introduce the robust PLC-5 platform, which replaced the PLC-3 and can still be found operating in some plants today.
PLC-5 controllers
The 1785 catalog number PLC-5 was launched in 1986 based on the Motorola 68000 32-bit CISC microprocessor and was designed to scale and support both centralized and distributed control architectures.Allen-Bradley defined a centralized architecture design as one that featured a single processor managing a plant where a distributed architecture contained multiple processors and user interfaces to manage a plant.
At the time of its release, a PLC-5 network would likely be managed by a VAX/VMS host or a panel-view operator terminal and programmed using dedicated programming terminal computers engineered by Allen-Bradley. As the PLC-5 platform evolved, it later adopted Ethernet connectivity (PLC-5/20E, PLC-5/40E, and PLC-5/80E) using a 15-pin Ethernet port, the first Allen-Bradley PLCs to do so.
Around the same time as the PLC-5 release in 1985, Allen-Bradley was acquired by Rockwell International (now known as Rockwell Automation), but the Allen-Bradley name and logo can still be found on many of Rockwell Automation's products.
The PLC-5 was an extremely robust platform and although it has been discontinued and replaced with the ControlLogix platform by Rockwell, it continues to operate in many plants. I have personally owned a PLC-5/40E and worked with plants that still operate these devices today.
Over the years of development of the PLC-5, Allen-Bradley released 15 versions of the platform, which were later categorized by Rockwell as Classic PLC-5 processors and Enhanced PLC-5 processors.
The PLC-5 Classic family of processors leveraged DataHighway Plus (DH+) and remote I/O for its communications. The PLC-5 Enhanced family of processors also had serial communications and Ethernet communications. Although the early programming software for the PLC-5 was DOS-based, Allen-Bradley eventually created a Windows-based programming environment for the PLC-5, called RSLogix5. The PLC-5 rack was entirely made of metal, making it very heavy and giving it an industrial feel. The following diagram depicts the PLC-5 rack with a processor and some I/O cards:
In the next section, we will discuss Allen-Bradley's first foray into the midsize control system market with the SLC-500 controller.
SLC-500 controllers
The SLC-500 was launched in 1991 and was designed to be used in smaller plants; in fact, SLC stands for Small Logic Controller. The SLC-500 is an integrated platform that contains the CPU, power supply, and I/O in a single unit. The SLC-500 platform eventually received communications support for DH485 (Data Highway) and Ethernet. The Allen-Bradley RSLogix 500 software was used to program the SLC-500s. The SLC-500 has been replaced with the newer CompactLogix 5370 or 5380 control platforms. The following is a diagram of the SLC-500 controller:
Next, we will introduce the low-cost control system solution from Allen-Bradley, the MicroLogix controller.
MicroLogix
MicroLogix and Flex I/O were launched in 1994. MicroLogix used the RSLogix 500 software for programming their PLCs (the same software used for the SLC controller family). The first MicroLogix unit to be introduced was the MicroLogix 100 PLC, which was released with several different combinations of I/O. Its creation was a response to the need for a low-cost automation solution with a limited feature set. The MicroLogix controller did not originally use a rack and modular cards, but rather a fixed set of input and output channels.
The following is a diagram of a Rockwell MicroLogix controller:
Over the years, Rockwell also introduced other new MicroLogix controllers, such as the Bulletin 1763 MicroLogix 1100, the Bulletin 1762 MicroLogix 1200, and the Bulletin1766 MicroLogix 1400 series. The 1100, 1200, and 1400 series controllers have reached their end of life and have been replaced with the Micro800 series or CompactLogix series of controllers.
You can always check the end-of-life status of a particular product by going to the Rockwell product life cycle page at https://www.rockwellautomation.com/global/support/product-compatibility-migration/lifecycle-status/overview.page.
Now, we are ready to introduce the ControlLogix line of controllers, which are the primary focus of this book.
ControlLogix controllers
The ControlLogix controller was first launched in 1997 as a replacement for Allen-Bradley's previous large-scale control platform—the PLC-5. The ControlLogix platform includes the Bulletin 1756 ControlLogix 5550 controller, the Bulletin 1756 ControlLogix I/O modules, and the RSLogix 5000 programming software platform (now referred to as Logix Designer). ControlLogix represented a significant technological step forward, which included a 32-bit ARM-6 RISC-core microprocessor and the ABrisc Boolean processor combined with a bus interface on the same silicon chip. At launch, the Series 5 (also referred to as L5 and ControlLogix 5550) ControlLogix controllers were able to execute code three times faster than the PLC-5. The L5 controller is considered to be a Programmable Automation Controller (PAC), rather than a traditional PLC, due to its modern design, power, and capabilities beyond a traditional PLC (such as motion control, advanced networking, batching, and sequential control). The ControlLogix platform is built on the ControlBus backplane, which performs like a mini-network and allows devices to be Removed or Inserted Under Power (RIUP).
The L5 has since been retired from the lineup, so we will focus on the newer L6 and L7 controllers in this book. Throughout this book, we will refer to the ControlLogix controllers as PACs, which are the modern-day equivalent of PLCs. In 2002, the Bulletin 1756 ControlLogix L6 processor was released with a more powerful processor, more memory, and the CompactFlash non-volatile memory card was added to the lineup.
Even though the ControlLogix platform is approaching its 20th birthday, it is still in the early stages of its product life cycle. For example, Allen-Bradley’s 1747 series SLC-500 family, which was introduced in 1989, is still available for sale today. Although it is no longer actively developed, the SLC-500 represents a product life in excess of 25 years.
ControlLogix represents a standard control engine with a standard development environment and tight integration between the programming software, controller, and I/O modules. This close integration greatly reduces the automation engineering development time and cost. The following diagram is of the L5 (Logix5550) controller, which was the very first ControlLogix processor card:
In the following section, we will introduce Rockwell Automation's Integrated Architecture product strategy and show you how the ControlLogix family fits into this bigger picture.