History of Allen Bradley PLC

The history of Rockwell Automation goes back to 1903.The Compression Rheostat Company was founded by Lynde Bradley and Dr. Stanton Allen and has an initial investment of $1,000.In 1904, Harry Bradley, 19 years old, and his brother joined the business.The Rockwell Automation factory equipment line brand name is Allen Bradley.

Allen Bradley PLC2 / PLC3 / PLC5  family

  • The first Allen Bradley PLC  in the market was PLC5 family.
  • PLC2, which was made in the 1980s and is now obsolete.
  • PLC3s were released in the 1980s also, followed by the PLC5, which is still used today, not widely. first large/wide rack system, with about twice the horizontal dimension of the SLC500.

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Allen Bradley PLC : SLC family

  • SLC500: In 1991 Allen-Bradley released the first SLC500. This platform was physically smaller than the PLC5, with a reduced instruction set.
  • SLC full name is “Small Logic Controller”. The first SLC, Known simply as an SLC500, was an integrated platform containing the CPU, power supply, and IO all in one package. with 1K of memory and was used in small i/o application

The first rack-based SLC was the SLC5/01.

  • The 5/02 and 5/03 platforms had DH485 (“Data Highway”) communications
  • The 5/03 was the first processor where logic could be edited online in real time without having to place the processor in program mode and download.
  • The 5/04 had even more memory and a faster communications platform called DH+ (“Data Highway Plus”).
  • The 5/05 had a serial port but also was the first to provide Ethernet communications.

This processor was used in a rack with power supply.

The I/O cards also available in a rack.

  • Different type of i/o card having digital, analog and special purpose I/O such as thermocouples and High-Speed Counters.processors had more memory, faster speeds, and enhanced communication capabilities.

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Allen Bradley PLC : Micrologix family

The Micrologix family used the RSLogix 500 for programming purpose.

This software same for SLC Family.

The first of the family introduce was the Micrologix 100, PLC that was made with several different I/O combinations. Same as the SLC500.

Its creation was a response to the need for a less expensive platform to compete with other manufacturers.

Also, like the SLC platform, newer variations became modular allowing for more configuration.

The Micrologix platform does not use a rack, modules are inserted on each end along with a terminating end cap.

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Allen Bradley PLC : Controllogix family

  • The ControlLogix Platform was introduced to the market in 1997.
  • This ControlLogix platform was rack based and very similar to looks the SLC, but main advantage that was faster than any PLC5 or SLC and had little a bit more memory. Rockwell introduces the first platform to use tag-based addressing.
  • Early ControlLogix platforms included the 5550 and L1 processors.
  • As technology and memory capacity improved these were quickly obsoleted in favor of the L60 and L70 series of processors with higher speeds and much more memory.
  • Communication cards for Ethernet, DeviceNet, and ControlNet are placed in the rack rather than using the port on the processor.
  • The processors still have serial ports or USB ports for programming and configuration. Servo control cards using fiber-optic SERCOS control also give the system more control over coordinated systems.

The Compactlogix platform was released in the early 2000s as a lower cost solution. Like the Micrologix, rather than being rack based, modules are added to the ends of the power supply or power/CPU module.

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Allen Bradley PLC5, SLC500, Micrologix : Software Details

  • The early software for the PLC5 and SLC500 platforms was DOS based.
  • Before the coming of Windows, Rockwell decided to create separate division Rockwell Software and RSLogix, Rockwell released Windows-based program was released.
  • The PLC5 platform is currently programmed using RSLogix5, while the SLC and Micrologix family (excepting the 800) is programmed using RSLogix500.
  • Communications setup for the programming software is handled using a separate software package called RSLinx.

The PLC5, SLC500 and Micrologix platforms use assigned registers and files for addressing and ladder files

  • bit registers are assigned as B3, addresses to the bit level in groups of 0-15, such as B3:0/5, (word 0, bit 5), B3:20/15 (word 20, bit 15) and so on.
  • Timers use the next register with addresses such as T4:2 (3rd timer in the register after 0 and 1), T4:5/DN (timer 5’s done a bit), T4:19/TT (timer 19 timing), and T4:12.PRE (timer 12’s setpoint). Various time bases are available such as 0.01s or 1s.
  • Counters are assigned to the next register (C5:0 and so on) with a similar addressing systems as the timers.
  • Integers or words are assigned to register 7 (N7:3 is the 4th available word address)
  • floating point or REAL data types are assigned to register 8 (F8:0 and so on). Not all processors have floating point math capability.
  • New registers can be opened for use with different data types such as B9 (bits), N12 (integers), F100 (REALs), or even S27 (STRING data types). Numerical use of numbers beyond F8 then are quite flexible and can be used as required.
  • Ladders or subroutines are assigned beginning with ladder 2.
  • This routine is created and called automatically.
  • As new routines are required they are created as ladder 3, ladder 4 and so on.
  • They must be called using a jump to subroutine command.

Upload program that not contains a comment. Because of this, an uploaded program with no documentation can be quite difficult to interpret.

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10 thoughts on “History of Allen Bradley PLC”

  1. The first Allen-Braley PLC was the 1750 PMC Programmable Matrix Controller, followed by the 1774-PLC, and then the 1772-PLC2. The I/O of the 1774 was the Bulletin 1778 Series, and the 1772 used the 1777 I/O initially, but that was replaced with the highly successful 1771 I/O system. The 1771 I/O system also introduced “Remote I/O.” That format was then used to develop the PLC-5, which fit into the 1771 I/O chassis.

    Allen-Bradley also introduced two small PLC’s in the 1980’s. One was developed in Highland Heights, Ohio (the PLC-4) and the other at the corporate HQ in Milwaukee, WI. Of the two, the PLC-4 was the more successful of the two.

  2. It’s funny what you can find on the internet. I worked at AB in Highland Heights from 1980 thru 1983 and was the software developer for the First HHT which connected to the PLC-2 controllers. It was developed using a CMOS 1802 assember, 8 instructions, and fit on a 8K Eprom. The code was actually inverted because for the chips to fit on the memory card the address runs had a be inverted. Also, with the start of PLC-3 and 4 development in 1983, C language was introduced as a high level programming language. My original manager, John Muzzey, made a real impact on my career as I remember working with him 40 years ago.

    • Hi Stephen Barlett

      Really appreciate your information. because I am not worked at AB :D.I have use AB Hardware and software.so YES this information based i have found internet and website.this is summarized post.Thanks for update

  3. Thank you for the article! I started in the industry in 1977. I remember the Allen Bradley PLC, (not PLC2 or PLC5) which was a huge machine!! The programming terminal was a T1 and weighed almost 40 pounds! I remember checking the terminal as luggage when I started up the Processor onsite. I have searched the internet to find this monster but had yet to find one. Great memories with this! I am trying to put together a little museum of the PLC I have used over me career. It is pretty cool the memories!

  4. I worked directly & indirectly for A-B for 19 years. So, let’s not forget the whole programming software evolution for these PLC’s…after the 1770-T2/T3 boat anchor terminals! I.e. Icom’s DOS based T3 series software for the PLC-2, followed by A-B’s DOS based 6201&3 software, with Icom in parallel developing the DOS based AI series programming software. Then Wintelligent5 for the PLC-5, then, BANG, Icom is purchased and Rockwell Software is born. So much history!


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