Blind faith in PLCs?(was Software Quality)


Thread Starter

Paul Jager

I have a new name for the PLC- it's a Pathetic Little Computer. Imagine any critical business or operation say a government service, a highly popular web site, banking services, etc. - running on PLC's. Obviously it can't be done. Yet from a computing standpoint this is what we blindly and faithfully do for industrial applications. This approach is hurting the industrial business. There is a lack of available computing power, lost opportunity of data distribution and computational flexibility, and finally the total cost of ownership.

It's not a simple question of Server more reliable than PLC, etc. My statement is that a server pair can and does deliver the required
reliability with benefits far exceeding what a PLC based platform can provide. I should point out that proper server SOFTWARE is a critical
element in the non-PLC equation. This market has some top solutions and is developing at a rapid pace.

In my travels to various sites I see a lot of scared engineers, with a personal fear of innovation. As a group we are not very open-minded. Those that combine business savvy and technical prowess are rare. Even rarer still are those that can interface with management executive.

Yes the PLC of course has less moving parts than today's servers. Taken for face value the PLC might eek out a server for uptime, but you are costing your company a hefty price overall with such loyalty to a Pathetic Little Computer.

Paul Jager
Mr. Paul Jager
Chief Executive Officer
M & R Automation Canada

Mr. Jager,

I earn my living every day helping people build industrial control systems with programmable logic controllers and associated networks and industrial control hardware. My customers, on the whole, appreciate my honest efforts to help them implement, troubleshoot, and maintain these systems.

Because I'm interested in the market outside my local field office, I extend that work to's Automation List. I like hearing what's going on in the rest of the industry, and I offer advice and assistance to many posters who have questions on systems in which I am an expert, both publicly and privately.

I have always respected the noncommercial nature of the A-List. You will never find an instance in the Archives of me recommending a product my
Company makes to replace a competitive product or to solve an unrelated problem. Because the A-List is operated and moderated through the good graces of Jennifer Powell and Ken Crater at Control Technology Corporation, they are free to enforce or not enforce their own ban on advertising. They respect that rule of restraint: Even when a posting has been an open door, I have never seen a CTC-generated plug for one of their controllers,
operator interfaces, or software products.

You have chosen to trample this principle at every opportunity. A question about a voltage spike defaulting RAM turns into "dump Allen-Bradley, use AutomationX". A question about a Windows NT service pack turns into "That wouldn't happen if you used AutomationX". A thread
about the quality merits of OSS you turn into "All PLC's are pathetic, and everyone who uses them is dumb and scared".

I am very disappointed with your posting this morning. I expected more professionalism from the CEO of an innovative company.

I took the time to read the fractured anti-testimonials on your website today. Your amalgamation of broken-English queries from the A-List is embarrassing. You even took an excerpt from a posting I made to assist a fellow with a severe installation problem and attempted to turn it into a comment on the quality of the SLC-500 controller line. I think when a potential customer turns to the Q&A section of a product site, he expects to see answers about your product, not an assortment of insults.

You're free to advertise your products in any way you see fit. AutomationX may well be the best thing since the pushbutton.

However, you'll do your reputation a world of good by leaving the defamation and sophomoric name-calling back at the water cooler.


Ken Roach
Sales Technical Specialist
Rockwell Automation Seattle District Office
[email protected]

Anthony Kerstens

Mr. Jager,

You know, your comparison (and new name for the PLC) erks me. In fact, your apparent attitude erks me.

I am a big fan of using technology appropriately.
The PLC and server are two different pieces of technology, each whose proper application is appropriate to differing circumstances.

As for "a lot of scared engineers, with a personal fear of innovation", you should consider their experience and concerns with the respect they are due. What you interpret as a "personal fear of innovation" may be something else entirely.

It is the rare engineer that I run across that doesn't love new toys. When an engineer shy's away from some piece of technology, rather than looking down over your nose at him, you should be asking why he reacted that way.

You may learn something useful.

Anthony Kerstens P.Eng.
Wow! This has gotten almost funny! After reading your post, I decided to head over to your website in hopes of finding something with a bit more substance. What I found was even more amusing. Your gleeful renaming of the PLC, and your outright hostility to them is more than apparent. I guess the reason this is funny is because while I was still in school, I was being told by people to not bother learning PLC's, since they will be gone in a year or less anyway. That was over a decade ago. I seem to
detect the same attitude from your site: PLC's are gone, and anyone who buys one is obviously clueless. I find nothing on your website that is
beyond nine months old. Have you been around longer than that?

OK. Now to address the posting:

I have a new name for the PLC- it's a Pathetic Little Computer.


Imagine any critical business or operation say a government service, a highly popular web site, banking services, etc. - running on PLC's. Obviously it can't be done.

Gee. you mean I can't load Oracle onto my Micrologix? Boy, this thing *must* be a piece of garbage! This is simply a case of right tool / right job. What about a 'mission critical' medical process? Or a food processor. I can guarantee that anyone who needs absolute uptime isn't running a PC control.

Yet from a computing standpoint this is what we blindly and faithfully do for industrial applications. This approach is hurting the industrial business. There is a lack of available computing power, lost opportunity of data distribution and computational flexibility, and finally the total cost of ownership.

A properly deployed system does not suffer from any of these problems. You cannot take a 10 year old installation, and compare it to a PC based
installation today, and then point out the differences. Where was -your- system 10 yrs ago? The point is that by properly combining the
technologies, be they PLC, PC, Network, HMI, etc. you can get a system that is far more robust than any one of these alone. Just as I would not try to use lights and buttons as the sole UI on a system of any complexity, you cannot honestly tell me that it is cost effective and justifiable to use a PC on *every* control system.

It's not a simple question of Server more reliable than PLC, etc. My statement is that a server pair can and does deliver the required
reliability with benefits far exceeding what a PLC based platform can provide. I should point out that proper server SOFTWARE is a critical
element in the non-PLC equation. This market has some top solutions and is developing at a rapid pace.

You were the one that made the reliability statement originally, I believe. What exactly do you now mean by "server pair"? Are you suggesting that the only way to make your system more reliable is by having two of them? Is
that cost effective against a Micrologix 1000 with 16 I/O points? Remember, you are the one saying that PLC's are useless. I am not saying
PC's are useless, just not the best solution for every problem.

In my travels to various sites I see a lot of scared engineers, with a personal fear of innovation. As a group we are not very open-minded. Those that combine business savvy and technical prowess are rare. Even rarer still are those that can interface with management executive.

I think you are mistaking 'fear of innovation' for fear of having to support some PC based nightmare whose rapid pace of development means
patches, upgrades, and bugs. The reason that induistrial controls are not on the bleeding edge is because we have no time for firmware and control software that needs constant patching. I have never experienced a PLC processor going into the equivelant of a 'blue screen'. (yes, I realize that PLC's have no screen. DUH! What I mean is that the processor doesn't just go out to lunch because an I/O driver was written wrong and created a memory leak, or whatever....)

Yes the PLC of course has less moving parts than today's servers. Taken for face value the PLC might eek out a server for uptime, but you are costing your company a hefty price overall with such loyalty to a Pathetic Little Computer.

"Might eek out"? ROFL! Let's see. at the last plant, we had to redesign the RSView apps and PLC programs so that the process could continue while
the PC rebooted, since it went down about every 4 to 6 months. RSView on NT. No extra software, no games, all service packs applied, blah blah
blah. It was a noisy environment that the PC was in. But guess what? Sometimes that is the environment that you get. Also, I am not costing my company anything by using the proper tool for the job. I guarantee that what I am doing with a PLC, you cannot do with a PC for the same price and same capabilities. And what I *do* use a PC for is the best use of a PC in *our* production environment

Looking at the website, specifically products.phtml, that looks like a lot of computing power. I notice that you have a hot standby machine in the loop. Is that to indicate that reliability is defined as redundancy? Also, you make the statement that:

"Field components are typically accessed via (E)ISA or PCI boards inside the control servers, an integrated Soft PLC enabling many different
combinations. Typical cycle times (to perform all the control tasks and send data to and from the field devices) are from 20 to 100 milliseconds"

A couple things on that. One, I have noticed that (E)ISA bus is disappearing from new PC's. How do you intend to support systems that still rely on (E)ISA cards to communicate? Or do those get dropped? What if my process needs a faster scan time? Most my stuff runs in the 5 to 10
msec time frame.

Lastly, on the website, I read your tirade against PLC's that is disguised as a FAQ.

You state:

"WARNING: For all of you out there wiring your 1761-NET-AIC devices to these terminals to interface to .. a SLC-500/01/02/03 processor beware. If you short the terminals the program in the processor is lost. "

Since most times, this is a one time connection, I feel comfortable comparing this to the time I was installing a CD-ROM drive at home, and
mistakenly plugged the power connector in upside down. Oops. Guess that is comparable to not paying attention and shorting the terminals together. Unfortunately, I couldn't just reload the program and go again. My PC did not have adequate protection against me being an idiot, and therefore I wound up buying a new CD ROM drive, and my power supply went out a month later. I believe the (PC) has a firmware bug. (Paraphrasing your website).

Of course, you answer your own imagined problem on the same page:

"(Of the) SLC memory corruption instances there were only a few in which a fat green wire to a solid ground didn't solve the problem."

Are you sugesting by comparison that I can run my PC solutions without a ground terminal?

And, of course:

My (P)athetic (L)ittle (C)omputer has never gotten a virus.
My (P)athetic (L)ittle (C)omputer never has operators loading games on it.
My (P)athetic (L)ittle (C)omputer never stops running because of an I/O driver getting corrupt.
My (P)athetic (L)ittle (C)omputer never has a hard drive crash.
My (P)athetic (L)ittle (C)omputer has near-zero boot time requirements.
My (P)athetic (L)ittle (C)omputer can keep a complete application backup in a EEprom for when the program does get dumped. Of course, My (P)athetic (L)ittle (C)omputer never dumps the program when handled properly.
My (P)athetic (L)ittle (C)omputer can continue to run without a screen.
My (P)athetic (L)ittle (C)omputer can continue to run without a keyboard.
My (P)athetic (L)ittle (C)omputer can continue to run without a mouse.
My (P)athetic (L)ittle (C)omputer doesn't rely on hardware that is revving every 6 months. I can find A (P)athetic (L)ittle (C)omputer **exactly**
like the 5 year old one that my forklift driver just speared on his fork.

And for the record, although reserves the right to post all of the discussions here on their website, I want to make sure that -none- of
my comments in this or any other posting get re-posted on your or any affiliated companies website.

--Joe Jansen
Controls Engineer

The opinions expressed here are mine, not my companies, blah blah blah.

Anthony Kerstens

Mr. Jager,

After reading Joe's comments, I must now compliment you.

By peeving Joe and me, you managed to make us look at your website, and actually examine your literature.

It's a marketeer's dream. :-/

Anthony Kerstens P.Eng.
Your post reminds of the programmer in Jurassic Park whacking together thousands of lines of code on his central computer to keep the dinosaurs in their proper cages.

A server and a powerful general purpose platform could be great in a pencil factory but a bad idea for a gas compressor station sitting out in the middle of the desert.

You might want to narrow down your definition of an industial application. When you realize the total cost of ownership includes cleaning up toxic spills, putting out fires, and assuming
liability for injuring people, the cost of a PLC doesn't even show up on the radar.

Jay Kirsch.Eng.

Clyde September

Pathetic they may be, but unlike soft PLC's, which you are undoubtedly marketing - the results of PLC 'computations' are visible all around - these lads get the job done for years on end, without too many tweaks and fiddles. (Referring to PLC logic, not SCADA..)

Clyde September
Dear Mr. Jager;

After reading your letter and visiting your web site the only conclusion I can come to is... it's Pathetic how Little you Comprehend Industrial Automation or what a very cheap way to try and generate traffic on your web site. Shame on you.

Dan Taylor
Systems Integrator
Logical Control Solutions
Any critical operation...........say like the Post Office mail sorters.........web site.......lots of life threatening equipment there, banking service........we all know how safety oriented that can get.......

Use the right tool for the right job ...........heart lung machines are not
built to control plants either......when you can make the PC operate my plant as long without fail as my PLC 5's (10-15 years) with 1 or 2 minor
hardware failures, usually caused by dumb humans (power spikes etc.) then I'll sign up.

In the meantime spare me your bias........your sounding like the Linux thread (day after day after day after...............................)


DAVCO Automation
"The Developing Automation Value Company"

Eduardo Manuel C. Cipriano

I do agree with Ken, and I would like to add that PLC, PC, and even DCS, has different Level generally we have 3 Levels the 1st is the Device Level which makes our devices intelligently useful in any ways like sensors, the 2nd Level is the Control Level this is where our PLC and DCS falls, and the Sort of PC based controller that CEO is promoting just Happens to Fall on the 3rd Level which is the Information Level you cannot mix Control Level and Information level it defies the General Foundations that has been there for many years, what I think is that that CEO should sit in the Library and do his Homework.........

[email protected]

Eduardo Manuel C. Cipriano
Sr. Systems Engr.
System Engineering Department
Yokogawa Phils. Inc.
I will stick to PLC's.
They are my friends.
Someday the PC will become a pLc.
When the PC becomes Loyal it will be a PLC.
Three letters mean better.
Three finger salute !
A posting like this can only work at cross-purposes to promoting AutomationX. Over the years I've dealt with scores of outside salesmen, and
those that carry on in this manner visit once, and are sent packing henceforth. There is a difference between vigorously promoting a new
technology or product line successfully, and alienating potential users with diatribe.

There are many situations where PLCs make as much or more sense as a personal computer-based system, especially when the I/O count is low,
and/or there is no need to provide HMI services beyond a few switches and pilot lamps.

For instance, I've used Siemens Logo! controllers (positioned between small bricks PLCs and programmable timer relays) for several small projects. It isn't fast - 50 ms, if memory serves (but doesn't have to be in these applications), and is 'programmed' using an electronic adaptation of wired up discrete logic devices (somewhat foreign to non-EE types), but does what
it needs to do, and, so far, I haven't had any soft or hard failures. The 6 input/4 output Logo! controller isn't a lot bigger than my fist, and is
programmed through front panel switches (although a programming cable and requisite software is available).

Perhaps this is a 'pathetic little computer', but it only costs about $220.

We stand completely behind what we said, and won't water down opinions.

The observations I summarized below are to us fact. It comes from visiting many PLC/HMI installs coupled with senior engineering experience at large scale DCS/PLC projects. We don't consider this to be sales or marketing
bullshit. It is what we believe in 100%.

If we were to build a factory, assembly plant, process or even create Jurassic park we'd do it with SERVERS and CLIENTS and be proud of it. No
PLC's. Don't need them, don't want them. The I/O is a must of course, take your pick.

However, I did not say PLC's are dead, or not required but said from a computing stand-point, there is a huge deficiency in the approach. I said in considering an install engineers should look at the business or organization as a whole, and the total cost of maintaining these effectively isolated and arcane computers. There is an opportunity cost to locking data in the hardware and making it largely invisible to the user base, the people of the company they serve. (But depending on how you look at things this may
benefit the control tech/maint. engineers and serve the vendors well).

Keeping on the Jurassic theme, imagine if it was as easy as using your Internet browser to view or modify all aspects of the Automation Servers (I
mean everything) that manage the environment and containment for the Tyrannosaurus Rex, the Diplodocus, or the water treatment system, etc. for the park, all within seconds, no matter where the location of user or server. And that's just one feature, there are dozens more with absolutely
enormous impact.

As one person pointed out, there certainly are cases where remote processing is a must, such as a well-site or if needed in really low cost conditions. Our preference then would be to manage this remote processing in the same automation environment as the server software that manages the rest of the facility. This approach would reduce total ownership cost (TOC).

As far as safety goes, the process itself must be safe, and the appropriate controls and backups in place along with the human issues resolved - such as alarm management. I've seen PLC and DCS systems responsible for some pretty big $$ damage and hefty explosions in my years. If you can improve the visibility to the process, the visibility of the controls, the responsiveness and convenience of the system and the ability to manage alarms effectively, you'll end up with a safer system overall, with less human error.

Paul Jager
Say what you want about the PLC. One fact remains. The PLC is popular and trusted for control. You arguing with industry won't change their minds anymore than they can change your mind. So instead of getting derogatory, be a realist and be constructive. The reality is that the best solution is PLCs and computers that work together. Thats where those serious about the industry are focusing and its where the market is heading. You can choose to profit from that trend, or you can buck it and get left in the dust.
And/Or GREAT BIG projects where there is NO Downtime (twice per year, top) and your performance is based on uptime,.... period. Also when SAFETY is a huge issue, and proven requirements are met. Also insurance companies balk at "cheaper" alternatives.

I am not anti-innovation quite the contrary, but I also am not dumb........and I like my job and reputation as they are.....So comments about the "scared engineers, with a personal fear of innovation" don't apply and if this is the tactics used to sell.....don't call......Lots to Learn.


DAVCO Automation
"The Developing Automation Value Company"


Jake thompson

I'll bet you are happy to see the amount of hits on your website, of course most are to just to see how blind you are to all the automation that is out there! Let me first say it is unprofessional to bad mouth other companies and technologies the way your website does.
Now let me say use the right tool for the right job! Of course you would not use a PLC to run a banking sytem, you also would not use a hammer to turn a screw. This does not mean the hammer is useless, it has its own place.

On your website you talk about memory problems with SLC500's, a good engineer would have tried to deal with the power problem rather than badmouth the PLC, there are devices out there that can solve these problems. Did you solve the problem? You cant possibly tell me you've never had a hard drive crash or any memory problems with your systems.?.?

PLCs have there place in this world and will be around for a very long time. Fieldbus technologies will improve and PLCs will become more network friendly. I belive the PC world is pushing PLCs in this direction, not wiping them out!

From what I can remember about the last century when the Y2K bug was around, not one of the hundreds of PLC based systems I have installed had a problem. I was visiting my pal Sam Adams new years eve. What about you?

I give you a challenge. For under $200 give me a reliable computer and with 10 I/O. I dont need an HMI, or networking, or anything fancy! Can you do it?
Jake Thompson
Controls Engineer


Curt Wuollet

Yeah, I don't go quite that far. I can see definite roles for PLCs _because_ they are small computers with limited scope.
The PLC concept is great as far as it goes and they are ideal for suitable applications like machine control and anywhere they would replace a box of hardwired relays, timers, etc. They are
easy to program for these applications and more reliable than what they replace. (speaking as someone who remembers hundreds of relays in one spot). My view is that they are being stretched
to where the model kinda falls apart and the extensions are not anywhere near as good a thing as the basic functions. Talking to a terminal or other serial device is an example where you have to work much harder on a PLC than on a PC. At best, it's done with another programming model tacked on. At worst, it's simply not available.
Definite purpose communications work fairly well as they can be hard coded for specific targets, but providing the general class, flexible communications that are an increasingly large factor in today's systems is nearly impossible without using coproccessors running a procedural language. This works but is a bandaid and
nowhere near as flexible and practical as using an platform that supports communications intrinsically and natively. Within the programming model and resources available, it is
impossible to accomodate unknown and future targets. This is a large part of the interoperability and compatibility problem that
is only partially mitigated by the fieldbus gambit.

Larger systems with more functionality are not served well by simply buying a larger PLC. Integration with PCs or other more general hosts is inevitable at some point. Here we run into the
same limitations in that it is possible to support only limited canned schemas and there is seldom much variety or flexibility. This is not a limitation of the host, but inherent in making a
PLC well suited for the tasks it is best at.

In the MAT/LPLC project, we are not so much out to replace PLCs. but to address theses latter problems with the outstanding versatility and flexibility of Linux. It's simply far more
practical to add PLC functionality to Linux than it is to try and add even a tiny fraction of the flexibility and versatility of Linux to PLCs. Linux is key, not because I'm a zealot, but because it's support for serial devices, networking, reliability, plus the advantages of Open Source for these types of programming and hardware work make it much more ideal than
the alternatives.

So, Paul, even though we're both Linux fans, you're kinda on your own on this one.



Around my plant I have dozens of little tabletop assembly machines. Each is controlled by a Micrologix 1200 PLC. Each has an identical control cabinent with an identical HMI panel. No two of these assembly machines are alike, each performs a different task, so each differs in the software in the PLC. But the control panels are virtually identical. PLC cost: $230.00. HMI cost: $199. Spare component inventory: almost zilch. The panels are constructed neatly and in compliance with all applicable codes, no spaghetti. Ever look in a computer box. Its a spaghetti chef's dream. No PC running any kind of software will ever do this job as cheaply, nor as reliably. An $20/hr maintenance tech can program it. I can build a panel today that is identical to one built two years ago. Can't do that with a PC. (You don't have to be on the bleeding edge of microprocessor technology, 2 year or even 10yr old technology is up to the task) The workspace footprint of the control panel is 1/6 the footprint of a PC, and assembly line real-estate is very expensive. One more thing - the emergency stop functions are simple, redundant, but fully effective: Deprive the whole machine, controller and all of power. When the danger is cleared, the machine can be operational in three seconds (very very important on an assembly line). You can't do that with a PC either.
The bottom line isn't about that plant you would like to build with servers and pc controllers because you personally just like the technology, its about a plant running efficiently, and cheaply so it can make maximum profit at minimum maintenance. My peers on the tech side of the businees have the nasty habit of forgetting that we (and every other company) are in the business of making money, not cool stuff. Besides the cools stuff they make isn't even their stuff. Meanwhile an improved bottom line means a bigger year end bonus, which means they can buy cool stuff they can personally own.
I have done several soft control systems and I found them to be no more cost effective than a PLC, regardless of scale, and on the small scale of less than 64IO, where 99% of the machines are, they are several times more expensive. An all too common mistake made is to compare the cost of the entire PLC (rack, processor, power supply, I/O and all) to the cost of a PC, when the appropriate comparrison is for the PLC processor only, because you still have to buy the IO anyways. When you do that you'll see the PLC processor is a magnitude cheaper.
Would you rather make a cool system at the expense of your own future income, or make a reliable system for about the same or less money and improve your future income?

Ralph Mackiewicz

I don't agree with the original idiotic and self-serving posting. The right tool for the right job is (obviously) 100% correct. Frankly, who cares about the sophistication of the computing power in a PLC anyway as long as it does a better job of meeting the requirements cost effectively? That's kind of like buying an IBM server instead of a Compaq server because you like the color black better than almond. But, at the same time we shouldn't simply dismiss PC based technology
as unreliable out of hand. My company has installed PC based gaging systems running in discrete parts manufacturing facilities with a
high vibration, dust, cutting oil, etc environment in place for over 10 years now without failure. These systems are directly involved in control actions of the gages and controlling hard automation motions. If used properly PCs can be used reliably and safely. That doesn't mean that PCs are right for every application either (as many of you have already pointed out).

The first prediction of the demise of the PLC that I heard was from a Giddings & Lewis engineer at a paper presented at one of the IPC shows in Detroit in the early 1980s. I think this joker will be about as accurate in his predictions too.

While I'm at it: I know we all like to make fun of the post office (undeservedly I might add) but their requirements for reliability and safety are no different than anyone else's. There are numerous human safety issues involved in ANY automation system that involves motion of parts of any appreciable mass. Their use of PC based systems does not jeapordize anyone's safety or their system's reliability.


Ralph Mackiewicz