PC based Control .vs. PLC

M

Mark Forrester

To the one who is doing a school project on bearing wear: As a Navy veteran, we used DVSIs for monitoring bearing wear and approximate length of time the bearings will last. I'm not sure if you can get a hold of them, but may I suggest that you try and contact Performance Monitoring Team of San Diego, CA or PMT, Norfolk, VA. They are only two teams in the Navy (that I am aware of) that use these type of devices. They are used to determine life of bearings on certain pieces of equipment on Naval Ships as well as utilizing Thermal Graphic Image devices, used to determine the stability of breaker panels for these devices. Good Luck!
 
In my opinion, nature gives very nice examples of control systems.

In nature, complex decisions are done by brain. simple and fast decisions are done by cerebellum.

I think automation systems will behave in same manner in future.

PC will act as the brain for complex decisions. And PLC will act as cerebellum to manage reflexive processes such as mechanical movements, emergency stop etc.

So, they can't compete; they will work together and support each other with their different capabilities.
 
F
PC doesn't necessarily mean running a buggy Windows OS. We've made advanced control systems on standard PC HW and using standard SW for years. Our Control Design Platform allows you to use stable Linux or real-time oriented RTOS-32 on industrial PCs for the control system. Programming is done in C++. Redundancy is achieved using the platform and the redundant hardware may even run a different OS. Check out the possibilities: http://www.icd.no.
 
C

Conrad Vinzens

It is now just about 10 Years ago that we had the first exchange on the issue PC vs PLC. (see the begining of the thread) In the meantime i moved on or up or whatever you want to call it :)

Gentlemen, let's be honest, it looks like we have not gone much further on this topic. Bill is still publizing new OS faster than the preventive maintenance teams can attend the equipment and the PLC's, said to be out of fashion are still going strong.

I got an other 15 years until my worklife will anchor in the harbor of pensioners. You think we might have found a solution to the issue by then?

Best regards to the automation community, from Conrad, who today only smiles if the Vista OS stops supporting the office package. At least no human beings are at danger, its just a forced coffee break, until IT fixed the problem :)

Mother earth keeps turning, regardless of what we do on it.
 
L
dear Conrad,

my father keeps on chuckling every time he reminds me that by year 2000, according to the scientists' proclamations in the '60s, seaweeds would have been the solution to the world's food shortage problem. I don't know what your today's diet is made of, but mine hasn't changed much since 1963 ;-)

A while ago QNX was mature enough, yet it is still used only in a minority of industrial applications. Linux RTOS seemed to be a smashing OS that would have pensioned PLCs in a matter of few years, yet... Uh, not to mention that even Linux-based HMI/SCADA solution seem to have an hard time.

BTW, last week a customer called me asking to evaluate solutions for the replacement of his Z-World and PC104 based solutions to Siemens PLCs. Might be just a coincidence, though.

Post again your question in 2019, maybe by that time we all will be working on PC-based systems...and eating seaweeds ;-)

Kind regards
Luca Gallina
 
C
Hi

Apparently you have missed a few things in the past 10 years. There has been great progress in PC automation since the discussion began. Progress should not be measured by the fact that PLCs are still used where they are the best solution. Their demise in those applications would not be progress. Progress should rather be measured by the use of PCs where they are the best solution, which was barely possible when the discussion started.

I have worked with some extremely serious, line of business automation that is done with PCs or similar computers and indeed this is an emerging trend. We tend not to see much of this activity because it doesn't involve the big automation vendors we all know and love :^) But when I behold a multi-million dollar printing press based on SBC's and Linux or bookbinding machines that use RTLinux for line coherence and control, something has definitely changed. 10 years ago, even 5 years ago, that would definitely not have been the case. But these applications are the_right_applications for powerful computers and reliable operating systems and the networking and throughput they provide. And that's not to mention the huge progress in embedded applications that replace automation as we practice it once volumes are established. And the new PACs have a lot more in common with PCs than PLCs.

It is quiet in the little pond of PLC industrial automation because change is nearly impossible with the entrenched interests and closed systems. But the world will be and is, simply rushing on by and bypassing this stick in the mud because the way is OPEN.

Regards

cww whose next job will be in the Open range.
 
J

James Ingraham

I believe there's pretty much a consensus these days that PCs and PLCs both have their place. Both have improved drastically over the last ten years. (Thanks, Moore's Law!)

I did want to disagree with you slightly, Curt. You said: "...a multi-million dollar printing press based on SBC's and Linux... 10 years ago, even 5 years ago, that would definitely not have been the case." I am aware of at least one multi-million dollar press based on Linux in the U.S. that was installed more than 5 years ago.

-James Ingraham
Sage Automation, Inc.
 
In reply to Curt Wuollet: I've also seen a lot of more recent equipment using "PC based" control. In almost all cases though, the soft logic systems where written by the equipment vendor, not a third party purchased item.

The users seem to fall into two categories. One set of users is companies who produce standard off the shelf equipment (rather like your printing press examples). The attraction for them seems to be based on a combination of support and technical capability. The support advantage comes from the fact that the product life cycle of the control system can be matched to the product life cycle of the machine design. They're never left with equipment they can't support because the PLC is no longer available. The technical capability comes from the fact that the control software is designed to support the exact features they need.

The other set of users are large custom machine builders. These users are more interesting in that they are the traditional PLC market. However a number of the larger ones have developed their own soft logic systems which they offer to customers as an alternative to traditional PLCs.

The attraction for this second set of users seems to be the fact that they can add a lot of capabilities into the basic control system that don't exist in PLCs. They can do things like report on machine performance stats as a built in feature. The production manager can now sit at his desk with his web browser and find out what really happened on the night shift, instead of listening to the night shift supervisor and the maintenance manager arguing over who was to blame. To do this with a traditional PLC, you generally have to add a PC. So they ask themselves, if you need a PC anyway, why not just have it control the machine while it's at it?

Another attraction for this set of users is that they build in the "routine" stuff as a standard feature set in their control software. This means they can program a machine for a customer much quicker than they could for a traditional PLC. Doing this with ladder logic (or IL) libraries is difficult, especially as every model of PLC is different.

What I've seen very little of is the soft logic systems from large PLC vendors that simply emulate their traditional PLC product lines. People just don't see any advantage to them since they don't do anything different from a PLC. This however is the sort of "PC based control" that people were talking about 10 years ago. *That* sort of PC based control has indeed failed to catch on.
 
C
Yes, one trend that is promising is the use of Linux. Even stripped down to the minimum, it provides functionality far beyond a PLC executive or any of the new "PAC"s. And I'll bet that some of the private systems written on top would be very viable products. The Linux folks they hire will surely see the sense in separating the engine from the application and we may actually eventually see several vendors using the same engine, either as a product or better, as a FOSS project.

It's a no brainer to see that such a project could easily handle logic, SCADA, even DCS without the nightmare of integration of many separates. If you look at the bulk of the issues presented here, many would simply cease to exist.

Regards
cww
 
In reply to Curt Wuollet: Where I would see an open source/Free Software solution fitting in initially would be with smaller to medium size machine builders who want their own soft logic or SCADA/HMI system like the larger vendors. They may have the technical knowledge to apply and extend a system, but may not have the resources to develop one on their own.

The software itself wouldn't be their business, but they would use it to support their real business. They could also use their own brand name with it. Eventually, the larger machine builders who have their own proprietary systems may stop supporting those and adopt the open source version.

This type of user can be expected to know what they are doing, and to be able to support their own end user customers themselves. That is the type of user that I think people should be keeping in mind with projects of this type.
 
C
I agree, but there would be enormous savings even for the big vendors if you could get even any two to avoid developing their own from scratch. And some I've seen would be much better off not developing their own.

Regards

cww
 
I have 30 years experience in Control systems including over 10 years as a Programmer Analyst developing PC based applications. I have much experience with PC based controls as well as DCS and PLC systems from various manufacturers. In my opinion no hardware is more reliable, robust or faster than a good PLC. In no situation has a PC based system ever come even close to reliability, performance or flexibility of a PLC (Contrologix or Unity being the best of the best).

As a consultant with a world class engineering company I (and my peers) would never in their right minds consider using PC based systems for final point control. PC's work well for advanced supervisory control but that is it. I hate even using Windoze based systems for HMI's as I believe that QNX is a far better solution. I have seen QNX HMI's run for 10 years without a reboot! No Windoze based console could ever hope to achieve this. PC's are for desktops or servers not control!
 
J

James Ingraham

Red, I have to moderately disagree, despite the fact that my company has almost entirely migrated away from PC-based control systems.

Red said, "In my opinion no hardware is more reliable, robust or faster than a good PLC."

Well, what's a "good" PLC? Are we putting smart relays in the same category as hardware redundant PACs? Are you comparing to off-the-shelf Dell PCs instead of industrial PCs? I've seen PLC hardware fail, usually for some good reason. I've seen PCs last a decade.

Red said, "In no situation has a PC based system ever come even close to reliability, performance or flexibility of a PLC."

PCs run circles around PLCs for performance and flexibility. Reliability is a maybe. They have PCs running nuclear power plants and medical equipment. QNX is on the International Space Station, and Windows boxes are in Mission Control in Houston. There's nothing a PLC can do that a PC can't, but the reverse is patently not true.

Red again: "I ... would never ... consider using PC based systems for final point control."

Well, that's fine. But lot's of people do, and have success with it.

Red: "...Windoze..."

Name-calling does not invalidate the tremendous success of the product.

Red: "I have seen QNX HMI's run for 10 years without a reboot!"

And yet you say that the PC is not reliable. You seem to have contradicted yourself.

Red: "PC's are for desktops or servers not control!"

There are a lot of counter-examples out there. I have quite a few industrial gantry robots running on PCs, including some even on Windows.

-James Ingraham
Sage Automation, Inc.
 
In reply to Red: So, your problem seems to be the OS used in those cases? I won't argue with you with regards to your MS Windows problems. Talking about that usually leads to a flame war here, so I'll just say that there are well known alternatives such as Linux and BSD which are at least as good as QNX if not better.

As far as the hardware is concerned, a lot of things have changed in the 10 years since the original post was made. You can get fanless motherboards and power supplies, as well as solid state drives for a very reasonable price. Some of the "embedded" hardware systems you buy these days are simply small form factor "PCs" using third party motherboards which were designed for embedded applications.

What seems to be the distinction in most people's minds these days is "PC = MS Windows". Apple's "Mac vs. PC" commercials haven't helped in that regards either, even though the Mac is using basically the same hardware today.

In practical terms though, what I would call a "PC" is any widely available general purpose computing platform that can run a 32 or 64 bit OS. You can get small laptops today that use ARM and MIPS CPUs, so x86 compatibility or the ability to run MS Windows can't be considered a criteria these days.

What I expect to see in future is the major PLC vendors putting third party embedded PC motherboards in custom cases and selling them as PLCs. They would do this for the same reason they have adopted Ethernet - cost and performance. I would expect to see this particularly in the lower volume applications, such as higher end PLCs, CNC controllers, etc. They would have a standard Linux or BSD OS supporting their software. The average user though won't know the difference.
 
C
I agree for the most part and in the past, certainly. But with the PAC and the SOC low power PC with SSD. They are converging hard.

Soon the only real difference will be the software, which in my opinion has always been a major factor. PC reliability has been slandered because of the crappy software people choose to run on them. With a small tight embedded type system, I doubt you would see much difference between the Wall Plug type PC's and a high end PAC. If you load crap on both of them, you wouldn't see much difference in reliability either.

Regards
cww
 
Windows is not stable at all, there is an article in the link below:

http://indanotes.blogspot.com/2008/12/pc-stability.html

Linux is much more better, I have never experienced QNX but I believe it should be a better alternative for automation.

I believe that PLC is designed for controlling motors and machines and it is the best alternative for controlling; but it is not all of automation.

A system is really automated if it is also automatically managed, and PLC is not strong in auto-management. For automatic management, PC is the only alternative today.
 
K

Ken Emmons Jr.

I think the distinction is a reliable PLC vs. an off the shelf desktop PC with [at least] two fans, hard disk drive, CMOS battery, cheap motherboard that was designed in a hurry and not necessarily tested well, and a morphing operating system.

If you have a well tested fanless computer with solid state disk and mounted as Read-only (Linux, QNX, embedded XP, WinCE) you are starting to get into PLC territory as far as reliability. In other words you are as reliable as your fanless PC box can be, which is probably pretty good in many cases. I would also add that an industrial hardened IO system is needed, whether it is a Wago/Beckhoff networked IO or industrial plug-in card.

I've used Keyence brick PLCs for 17 years and not had a single failure (Other than one or two shorted IO points which was not its fault).

We've also used Mitsubishi Q series hardware for the last 5 years or so and not had a single failure there as well. Neither of these systems are without fault, but as far as reliability they are good.

So in the end both *Can* be made to be reliable, it just depends on who is implementing it.

KEJR
 
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