the great PLC vs. PC debate...

Before I begin, let me apologize in advance for beating a dead horse.

I'm so sick of hearing about PC's replacing PLC's. We had an Intelligrated rep in bragging about their new sorter that uses a laptop running a C# program instead of a traditional PLC to control the process and management was eating it up. The thing sounds pretty amazing mechanically, but dear god, who in their right mind would buy a system thats controls need to be upgraded every 3-5 years and relies on magnetic media?

I hate the shift I see towards the PC. We have two systems that are controlled via Rs-View and i'd love to kick the PC's to the curb and replace them with a nice HMI touchscreen, but the stupid things use VB code to handle some barcode scanner / printer action and it would take more resources than my boss will give me to make the transition. I hate having to 're-boot' my state of the art packing line every 3-4 weeks when the pc based HMI freezes up.

I just don't get it... sure PCs and high level coding are amazing, but it just seems like your sacraficing so much reliability and long term support by shifting your controls to them.

Anyone else seeing this rather annoying shift, or is it just in my companies niche Internet distribution center environment where this is happening?

I remember a fad many years ago called Steeplechase. A couple copies of the software sits in our library gathering dust. I haven't seen an installation or the mention of it in a RFQ in quite some time.

Maybe the newbies that are specifying PCs to replace PLC don't have the advantage of previous experiences and knowledge of the shortcomings.

monkeyhead said:

Anyone else seeing this rather annoying shift, or is it just in my companies niche Internet distribution center environment where this is happening?

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Show me a PC that hasn't been rebooted in 10 years. Most likely it hasn't actually been turned on in all that time either.

If you're going to use a PC for control, it had better be industrial hardened and have an operating system that's geared toward control. In effect, it had better be a PLC.

AK

I haven't had a plc infected by a virus yet. I had pc/hmi that the plant somehow got infected through the use of the floppy drive. SCARY!!!!!

I have heard there is a brewery, controlled by RA's SoftLogix (rack PC). Something like 20K IO's if I remember correctly. Communication done via ControlNet. But definetly it is not cheaper than PLC.

if you use a PC for controlling the machine is that harder to program than a PLC??

if you use a PC for controlling the machine is that harder to program than a PLC??

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Not at all, if you use a PLC family, that has very same programming package for PLC and PC (for example software I mentioned in the last post).

One of our printing presses has a UV drying system with a PC based HMI. At least once a week I have to reboot the PC.

Dale

I've inherited several machines that run on Entivity's Think & Do software. I am less than impressed.

Reliability doesn't approach that of our PLC's that run on other lines (reboots required fairly frequently).

I would never spec PC based control intentionally . . .



That said, I use PC based HMI's (or really SCADA's) all the time. I do my best to program them with the mindset that they shouldn't be needed 100% of the time, and so a reboot should NOT effect machine operation (and can occur at any time).

Marc

I've seen this PC based control concept resurected many times over the years. A few brave (or foolish?) souls try it, and find out the reliability isn't there, the total project cost is the same, or worse if you count lost production and increased engineering and service. The word gets out, and PC control drops out of site.

Then the idea goes away for a few years until someone makes a big Public Relations spash with "the NEXT BIG THING". The trade press, like the tabloid press, has to write about something, so they start to put down a lot of ink on the concept and a few brave (of foolish? souls ......

I've done som PC based stuff that worked OK, but I didn't rely on Windows, and I didn't rely on hard disks. If you have either of these two in the system, you had better make sure you have all critical functions handled someplace besides the PC.

I believe the only thing a PC is good for is the fact that you can multitask document and media applications, PC's were never intended to handle production, hence the name "personal computer", if it was meant to handle automation, they'd call em something else. I've used RSView extensively and found it to be a good program, but, you're always limited by the instability of the PC you have it running on. Not to mention some knuckleheaded operator who has way too much access to the PC deleting or corrupting the files. With PLC it's a little more of a task to hop onto the program, but, as long as you remove solitaire the operators won't mess with it anyway.

I believe the PC issue will be a fad for a long time to come. Like bellbottoms. It takes some people a few times to be reminded how much they dislike something. That must be why every 6 months I mess up and try to eat Grape-nuts cereal, they're the worst.

I like Grape Nuts.

Onct upon a time I built and sold PCs. Little over 5 years ago I built a server/webserver using Linux and Apache with 4 Cheetah 10000rpm SCSI hard drives.

I screwed up I guess, the system has not been rebooted or shutdown since I installed it according to the customer. I tried to get them to let me do an upgrade but they didnt see a reason to spend the money.

Overall a PC can be as reliable as any machine...the OS is a different story. I know of several DOS based systems that have no problems. I believe if Linux was more accepted and developed more in the SoftPLC area it could be as reliable as a PLC.

Personally I think the PC will eventually overtake or replace the PLC in industrial applications when everyone stops Gates thinking.

They are both machines and I have had to restart PLCs many times to get a machine to run....ie turn off system and turn back on. I have had to replace whole units because one input or output had gone bad. A PLC can have problems too.

Just to mention, we had a Novel server that ran for 5 years uninterupted, Finally shut it down in early 2000.. However I'm not about to risk it with our machines..

Elevmike and RSDoran,

I agree with what you're saying. I would have to say that OS does have a lot to do with it, but, you both also mentioned you didn't have problems with "servers", I believe that in any application you'll have a lot less trouble with servers vs. regular PCs, they're not as prone to locking up because they don't interface with people as much as your run of the mill PC, and they're usually not walking the fine line of RAM versus how many applications are being run. We use Dell servers in our facility for the Honeywell Plantscape and we rarely have problems. But, our PC's are always giving us hell because Bruno the operator spilt a coke on the hard drive, or something along those lines. Not to mention, designers usually put servers in a safe environment (away from day to day operations).
I like Grape-Nuts, too. Every couple of months I have to put down new gravel in my driveway, and they fill the bill nicely. If I need that much fiber, I'll eat treebark. It tastes better and is less filling.