ritzspeed

PLC vs PAC

15 posts in this topic

What is a PAC? How is it different from a PLC? Does Rockwell/ Allen-Bradley have some/any of PAC?

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Marketing tool. New and improved features. http://www.controleng.com/single-article/plc-vs-pac/44448cf771be09bff7115c621633bd94.html AB's ControlLogix is called a "PAC"

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In the GE-IP world the PAC line of products is based on high end processors and lots od RAM. Most use Intel Chips same as many laptops with 5 - 20 Meg of RAM. This stands for Process Automation Controller and in geneeral terms marries the 'PC and the 'PLC' into one package.

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Hi ritzspeed: There are many vast differences between a PLC vs PAC, and I have written much on that specific topic. I list a couple resources below for you to learn more, but in short ... "PLC: Uses one microprocessor chip to process ladder logic (electrician friendly) and possibly 1 or 2 other programming languages on a custom architecture designed for quick minimum operating system. An architecture/processing method commonly referred to 'Scan Cycle', that polles real world input cards, processes ladder logic, then updates real world output cards." "PAC: Is an industrial grade computer (2 or more full blow processors) that contains a PLC (emulates a PLC anyway), motion control and other standard computer architecture features. It does not have the 'Scan Cycle' that make PLCs what they are, but instead does multitasking like standard computers do, has all 5 IEC programming languages, one of which is structured text (computer programmer friendly). Each real world i/o card is its own device on a network with it's own microprocessor. So real world i/o is updated on a time based frequency, not waiting until logic/code are finished being read. (So if you use ladder logic for example, an input can change states will in mid 'scan' of ladder logic subroutine for example.)" After you study thoroughly the 2 resources below, you will see there are many more additional and significant differences between the PLC and the PAC (speed, memory size, firmware, etc.) ... For general overview read http://www.controldesign.com/articles/2015/what-oems-dont-tell-end-users-about-pacs/ For a sample of what one needs to learn related to the PAC, demonstrating the stark difference compared to learning the simple PLC, see http://plc-training.org/pac-automation-controller-BP8.html. Hope this helps shed a little more light on your question. Edited by BIN95

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Agree with this. Typical verbiage, to self-declare own product as "high end", like "magnum" in firearms or "pilsner" in beers. All the differences are quantitative and not all are that important or really necessary. And some are even disadvantageous, like the mentioned I/O update in the middle of the scan. Edited by Sergei Troizky

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That is like saying the Term "computer" is just sales verbiage for a high end Calculator. Yes, a computer does have a calculator in it, but a computer is called that instead of a calculator because it is a completely different electronic architecture, for usage and learning, it would be confusing to call a computer, a calculator. The same is true with a PLC (micro controller) and a PAC (industrial grade computer), from a usage and learning perspective, it is important to distinguish between the two. The electronic architecture and processing is completely different. (see my post above and its resources to learn the difference.) Most major PLC vendors also have their own line of PACs too.(Its not just a Rockwell thing, not just a Control Engineering Magazine thing, not just an ARC or IEC thing. There is a reason the industry distinguishes between the two.) I wonder if people referred to DCS when it first came out as a PLC, claiming it was just a sales verbiage for a fancy PLC. Edited by BIN95

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An electronic calculator is a computer. It has all architectural components to be a computer by definition: CPU, memory, I/O devices. The most advanced ones are user-programmable for specific calculations. Any difference with personal computer is only quantitative. So, they might be sold as "handheld computer", "pocket computer", etc. And this is exactly what I meant for PLC vs PAC- a PAC is nothing else but just more powerful PLC. Edited by Sergei Troizky

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As is a digital watch, although it may have limited functions.

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LOL . I am feeling this is not going anywhere, but like I mentioned before it is important to differentiate "for usage and learning" purposes. You may be trained and experienced on the calculator so you can add up your grocery list, but if you then hand that person a laptop computer when they ask for a calculator, they may be hard pressed to even find the calculator on the computer. And on the flip side, if someone wants to write a SCADA computer program and ask you for a computer and you just hand them a calculator, that won't work either. From a "usage and learning" perspective, it is important to distinguish between the two device. they did not just name a computer that for sales so they could get more money. Also a devices architecture is not defined just by the parts it contains, it is a combination of how those parts are wired/programmed together, detail of those individual parts and how they interact. A microwave has a CPU too, but you will not be doing much math, or spreadsheets on it. ? The CPU as a qualifier is too vague. The space shuttle has a CPU in too, but when I ask for or ask to be trained or even talk about it, I don't use the term "the calculator took off to the moon today. ha ha It would be like saying, it has a IC chip, so there for all products that have one should be called the same thing. The CPU in a calculator is a very limited custom microprocessor, a computer has a full blown processor (2 or more now days) so it multi-task. (much different architecture and only emulates a calculator) A PLC has a custom microprocessor (but much more powerful than the calculator's), a PAC (industrial computer) has 2 or more full blown processors in it and multi-task and does not have a scan cycle (it just emulates one). From a "usage and learning" perspective (especially if you are programming one), this is a critical to understand and identify them as two different devices. ?A computer can do anything a calculator can, but not the other way around. A PAC can do anything a PLC can, but not the other way around.

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so other than 'higher performance' what is the distinguishing feature of PAC when compared to PLC? what can PAC do that PLC cannot?

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Multi-task is the most dominant thing a PAC can do that a PLC can not. (PLC is limited by only using a microprocessor specifically designed on to use the 'Scan Cycle' processing architecture.)Motion control is another (being built into the PAC).Having multiple process modules in one rack is another,Save tags (symbols) to the actual PAC is another,set the update frequency of I/O modules, is another.I/O modules being accessible on the ethernet network is another. (The backplane of a PAC is an actual ethernet network, where a PLC's backplane is just a serial bus.)Communicates in 32 bit instead of 16 bit like PLC does.But performance is nothing to take lightly either, speed, memory, all 5 programming languages, not just a couple. Programing environment and architecture structured after computer programming environment conducive to task prioritizing, modular, and other multitasking features and techniques. There is so much, I am probably overlooking some too, being in a rush. this is just what comes off the top of my head. hope it helps.

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PAC = PLC on steroids Most companies use the term to differentiate newer more integrated system which can do more than a typical old PLC can. It's just a name. Mitsubishi calls them 'Automation Platform', Omron calls it 'Machine Automation Controller', everyone kinda makes up their own terms. In the end it boils down to making people want to think it's more capable than a PLC.

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A PAC is a PLC. Plain and simple. Time marches forward, and the power of our varioius toys increases, but the essential function remains the same. Yes, there is now integrated motion, and various languages, and multitasking, but that is only a result of better processors and cheap silicon. Going by BIN95's description, we should be calling our PC's something else today, since they are so totally unrelated to the IBM-XT running DOS. A LOT changed since moving from the 8 and 16 bit processors.

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If you changed one word in your above statement, I would agree. If you change "think" to "know", so it reads ... "In the end it boils down to making people want to know it's more capable than a PLC." Just as we call a computer a computer rather can calling computers "calculators" or "data processors". To quickly identify there is considerable differences when talking to others.

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Actually an IBM-XT is called a computer just like today's computers are called a computer because of the architecture, they are both the same, just speed, size, functionality and accessories of that basic architecture have evolved. It is still the same basic architecture. In contrast, a PLC has a micro-processor restricted to 'Scan Cycle' type architecture. A PAC is a computer architecture.

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