Today we continue to review the history of PLCs and the evolution of industrial automation. For the first part, see: The History of PLCs and the Evolution of Industrial Automation (Part One).
Part Two:
Siemens entered this field in 1976 with the launch of a product called S3. Prior to this, Germany had used an S series controller. However, the first commercially available Simatic (Siemens’ automation brand) controller was released in 1976. Subsequently, the S5 series—a very powerful platform from Siemens—was launched in 1979. It had a significant impact in Europe, becoming very popular and serving as the foundation for many other European controllers. If you start to explore different platforms like Bosch and B&R, you will find that they heavily utilized the same technologies as the Simatic S5. In fact, the S7 series (released in 1994) also inherited many timer technologies from the S5. The S5 introduced a version called 135U in 1984.
Meanwhile, another Japanese conglomerate—Koyo—began manufacturing ELCs (Electronic Logic Controllers) for itself, the Japanese market, and others. Consequently, GE launched a PLC model called the 300 series around 1985, which was produced by Koyo. At the same time, Siemens did something similar. The Simatic TI-305 was roughly equivalent to Koyo’s 300 series. Thus, GE, Siemens, Koyo, and Texas Instruments—though Texas Instruments was not a major player in the PLC market, they did have a TI-305, which was also manufactured by Koyo. All these products used the same programming techniques and instruction sets.
Meanwhile, Modicon was still striving to develop. They released a very powerful controller called 984 in 1986. The 984 stood the test of time and was used until the 1990s. The GE-9030 was a fairly powerful platform for General Electric, also released in 1990. At the same time, personal computers (PCs) began to become quite popular and their prices were continuously dropping. Therefore, there was DOS software available to program most of these controllers. Although DOS was still not a graphical programming language, you still had to input commands, but people could have their own laptops and small screens. You could type mnemonic instructions using the keyboard. You no longer needed to purchase handheld controllers or large programming devices like those from Allen-Bradley that had to be wheeled around due to their large cathode ray tubes (big TVs). When I started working in industrial automation around the late 80s to early 90s, PLCs were roughly like this. I would see these carts being pushed around in factories. I also saw many manufacturing facilities.
Interestingly, at that time, almost everything had very little memory, and programming was quite difficult. You operated using mnemonics. You would design programs on paper, write down your circuits, and encode them into the controller by converting the graphical representation of ladder logic (which is a sequential operation of relays, timers, counters, etc.) into a string of mnemonics. When I learned my first PLC platform, I first studied Eagle Signal and Omron. I attended a course from Omron, which had a handheld controller. You would draw your circuit diagram, then input “LOAD” followed by an address. If you wanted to trigger an output, you would input “OUT” followed by your output address. Of course, you also had internal memory, which is internal relays, and the original Modicon controllers had internal memory. But the original Modicon had 4K of memory to store everything: program memory, I/O memory, internal relays, logic, all of which had to fit within 4K.
As technology advanced, memory reached around 16K. When I say “K,” I mean kilobytes, which is thousands of bytes. In fact, a kilobyte is usually rounded to 1024 due to binary reasons, right? 1 plus 2 plus 4 plus 8, where one multiplication value is 1024. So 1K of memory is actually 1024 bytes of memory. At that time, many different platforms had an interesting point: some of them, like Modicon, insisted on using an 8-bit or 1-byte memory platform as a base. Meanwhile, Allen-Bradley migrated early to 16-bit because they recognized that a 16-bit word could store up to 65,000 values, which became very important, especially when dealing with negative numbers.
Thus, timers in the 1990s typically ranged from 0 to 32767, which is essentially binary 2 to the power of 15. The reason it did not reach just over 65,000 is that you had to be able to represent negative numbers, so they used signed decimal representation. This allowed you to range from -32768 to +32767. So you had a wide range of negative and positive numbers to work with. Your timers could run up to 32000. Of course, this became a problem because if you were timing in milliseconds, you could only time for about 30 seconds. So they used time bases. You could have timers from 0.01 seconds to 10 seconds, where one clock cycle is 10 seconds. This allowed you to time for hours or even days. If the clock ticks every 10 seconds, that would be 10 seconds.
10 seconds. The clock is ticking. That would be 10 seconds multiplied by 32767.
As time went on, in the 1990s, PLCs replaced most manufacturing applications unless they were very simple. Because PLCs were more economical than connecting all the relays. The cost of solid-state components had decreased. At this point, PLCs had been primarily based on solid-state transistors since the late 1970s to early 1980s. Therefore, PLCs at this time were much smaller than the original Modicon and Allen-Bradley PLC-2. Allen-Bradley’s PLC-5 was released in 1985, which was their main PLC for large factories. It had more memory. But by 1991, they launched a platform that I first used in Allen-Bradley called SLC500. PLC stands for Programmable Logic Controller, while SLC stands for Small Logic Controller. So at that time, this was a smaller version of the PLC-5. Its instruction set was slightly simplified, being basically the same as the PLC-5, but they removed some of the more complex instructions. It did not have as many PID (Proportional-Integral-Derivative) functionalities, etc. It had regular PID, while the PLC-5 had enhanced PID instructions. The SLC500 eventually also adopted PIDE.
Interestingly, the SLC500 was released in the same year as GE’s 9070 series. At the same time, Omron launched the CV series, which was also the series I used when I was learning in the early 90s. I studied the C200H platform and CV series, which were released around 1986. The CQM1 was released in 1993, and I think that was when I first attended Omron’s courses. In the 1990s, many platforms flourished. Siemens launched the PCS7 system. They had a computer-based platform around 1997.
So at the turn of the century, the main platforms were likely still Allen-Bradley and Siemens. Schneider acquired Modicon in 1997. They also became quite popular in Europe. Schneider also owned several other PLC platforms. Schneider actually acquired Square D, which at the time owned Modicon, having acquired it from Gould. So these companies began to acquire each other, which became quite interesting.
Then the remaining giants were Siemens. Allen-Bradley was acquired by Rockwell in the 1980s. So Siemens, Rockwell, and GE merged their control components with FANUC in 1986. Thus, Rockwell, GE, FANUC, Schneider, while Siemens remained Siemens. Mitsubishi became very popular in the 1980s and 1990s, especially in Japan. I think they are the most widely used platform by Japanese engineers in Japan. Even today, they still seem to prefer Mitsubishi controllers. The Mitsubishi Q series was released in 2001.
Let’s talk about two interesting and noteworthy things. In 1994, the International Electrotechnical Commission (IEC) released a definition for PLCs, namely IEC 61131-3, which defined the instruction set, timers, counters, and different data types used in PLC programming.
Quickly, many existing PLCs did not comply with this standard. For example, they stipulated that all timers should count in milliseconds. And as I mentioned earlier, the timers at that time were 16-bit and could only count up to 32767. Therefore, they could not count in milliseconds without becoming 32-bit timers. Moreover, in many cases, the computers at that time could not even run the software required for the 32-bit operating systems that emerged around the year 2000. Therefore, around the turn of the century in 2000, most companies began to launch PLCs that fully complied with the IEC 61131 standard.
For Allen-Bradley, this was the ControlLogix series. They still retained the SLC and PLC-5. They did have MicroLogix, but ControlLogix L1 was released in 1997. Of course, in the US, since Allen-Bradley was such a significant player, many automotive companies and major manufacturers began to switch to the ControlLogix platform. The ControlLogix platform is a 32-bit system. They no longer used integer-based mathematical operations but instead used 32-bit mathematical operations, which is very useful for real numbers. If you want to represent a real number, you need 32 bits. Before this, you had to combine two 16-bit registers or four bytes. You could combine these four bytes together. This is also why Siemens programming is somewhat complicated, as they had to reserve memory areas and define which four bytes would be used to store a real number, for example. So memory was somewhat fluid in that regard. You could assign different data types to your byte memory or M memory, as it was called at the time.
Meanwhile, communication also became increasingly powerful. At the turn of the century, most devices transitioned to Ethernet. IEC 61131 may have truly been a significant event that changed the direction of many controllers.
Another event in 1994 was that Koyo entered the US market. There was a person named Tim Holman, whom I was fortunate to meet in the 1990s. He founded a company called PLC Direct, which began selling PLCs through mail order at quite low prices, which were actually just Koyo-branded PLCs. Of course, I previously mentioned that Koyo also manufactured for Siemens, GE, and Texas Instruments. By the late 1990s, Texas Instruments was no longer a major player, having exited the business, but PLC Direct continued to launch these controllers based on the 300 series. Many other companies had abandoned those products. The TI 305 and GE 305 had basically exited the market. GE had shifted to their 90 series, etc. TI had basically disappeared. Siemens was still using their S5 controllers, so they were no longer using the TI 305 model, i.e., the Simatic TI 305.
So PLC Direct suddenly became the main player for Koyo PLCs. They launched the 200 series, which was a very small controller, comparable in size to Allen-Bradley‘s MicroLogix series or Siemens’ 200 series. So they had their own small 200 series, while their 300 series was quite similar in size to the SLC500, belonging to the mid-range controllers, or comparable to the sizes of S5 and S7. Then their large controller was the 400 series, specifically the 405. I was fortunate to have worked with some of these in the late 1990s. I was again lucky to have worked at a Koyo plant in our area. They used a lot of direct Koyo PLCs, branded as Koyo rather than PLC Direct.
At that time, mail order was a new thing. But you could receive your PLC from Atlanta within a day or two, with all goods shipped from Atlanta. Their technical support was quite good at that time. However, they would not come to your site to help you solve application problems. You had to call them and use remote technical support. This is one of the reasons why Allen-Bradley maintained its lead in the US. They had a very strong distribution network, and their technicians or PLC experts could come from local distributors to help you. They also had technical support, and GTS (Global Technical Services) would come to your plant to provide assistance, of course for a modest fee. But Allen-Bradley undoubtedly became the major player in the US market. Siemens did not really start making progress in the US market until the 2000s. Of course, European manufacturers in the US would use Siemens products. But it was quite rare for US companies to directly use Siemens equipment and specify it for controllers. So Allen-Bradley was the giant in the US market, and GE was also a giant in the US market, while Mitsubishi and Omron primarily operated overseas. Of course, Panasonic also had PLCs. Many large electronic manufacturers, such as Hitachi and Toshiba, had some form of PLC. I mentioned TI, Texas Instruments. This is an American electronics company. But Allen-Bradley did push most other participants out of the US market. Now it is estimated that Allen-Bradley may account for 60% to 70% of the installed base in the US. Once you have such an installed base, it is very difficult to switch an entire factory to a new platform.
In 2000, all these platforms began to comply with the IEC 61131 standard.PLC Direct was renamed AutomationDirect in 1999 and launched controllers that complied with IEC standards. Now they have the Productivity series. I remember they launched the Click series sometime in the early 2000s. In the late 1990s, I was still using Automation Direct’s Koyo 205 series in many applications. For those looking for low-cost systems and not wanting to pay for software, Allen-Bradley, Siemens, and even GE and Modicon Schneider’s software were quite expensive. Entry-level software was costly. So for those looking for low-cost PLC software, Automation Direct was a good platform. OMRON’s software was also not too expensive. OMRON became a major player in the OEM (Original Equipment Manufacturer) space globally. I saw many devices from Italy, Europe, and even the US using OMRON PLCs. Part of the reason is their extensive distribution network, and part of course is cost. Getting into the CS and CJ series is much cheaper than getting into Control Logix or TIA Portal series.
Speaking of TIA Portal, Siemens performed very strongly in the S7 series. It still did not fully comply with the IEC 61131 standard. But then in 2008 or 2009, they launched the S7-1200, primarily to replace the Siemens 200 series. Thus, the S7-200 was replaced by the S7-1200. At the same time, this was also a 32-bit operating system. You no longer had to worry too much about all the memory mapping. So TIA Portal (Totally Integrated Automation) is their latest platform. The 1200 series is still a smaller controller but does have a lot of networking capabilities. You can connect many Ethernet-based remote I/O devices. They had PROFINET since around 2000. Therefore, PROFINET was a faster method of remote I/O control at that time. But TIA Portal remains their main platform for PLCs that comply with the IEC 61131 standard.
(To be continued)
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