Pc Logic Vs Plc Logic

awilken

Member
Join Date
May 2004
Posts
9
I am very new in the industry of Logic programming. I have noticed 2 major types of programming PC & PLC. Which one should I study?

It may Help if I give you some back round information. I am working with large diesel engine control logic, mostly ice cube relays, RTD sensors, pressure sensors,modbus data.
 
Which one should I study?
What is your goal ?
To learn about general "logic" problem solving ?
Or to learn about logic controls in an "industrial" context ?
Or to solve a specific problem (maybe for a Diesel engine generator) ?
Or ...
 
What should I study

I am looking for data collection, graphing,HMI, Some engine control logic, Start-stop, Alarm shutdowns, logged events and alarm history.

Is the industrial market moving towards PC type logic. Can PC controls operate 300ma relays with no problems.

I hope you are able to get some idea what I am looking for.

Thanks for the replay!
 
This is a somewhat a matter personal opinion however I would suggest a PLC is more suited to this application for the following reasons...

1. PLC are most robust in an industrial application, they are less susceptable to vibration.

2. In the event of power loss they can be configured to auto restart and the delay for the restart is seconds compared to minutes for a PC based system.

3. PLC dont use moving parts, where I work PLCs that were installed in 1985 are still providing trouble free service with little or no maintenance.

However for HMI, datalogging (in a user friendly manner), graphing, logged events and alarm history a PC based sysem is more appropriate. Generally these HMIs are industrial spec computers and the best of these are generally solid state ie they dont use hard drives instead utilise NVRAM to stor the data.

For an application like this a small PLC such as Micrologix and a HMI like Panelview plus would be spec'ed.
 
Well now!

I am looking for data collection, graphing,HMI, Some engine control logic, Start-stop, Alarm shutdowns, logged events and alarm history.

In the situation you describe, a PLC will work for a limited amount of data, graphing, logging stuff. A PC is better suited for the amount of data handling you are requiring. You may want to do all the logic, alarm stuff with a PLC and the other stuff on a PC running HMI software such as Wonderware. Then again, depending on how much money you want to invest in the system, you may also consider a small DCS. There are some fine ones out there and they will do all the things you require in one industrialized package and you get single source responsibility. If you put a system together based on several pieces of equipment from different manufacturers, you may get in the finger pointing situation should a problem arise. Do some internet research and talk to some vendor reps.
 
Life is not just white or black, it's bunch of shades of gray
(and colors...).

You have to ask yourself few questions before you decide on
one or the other type of product. First thing you need to know
is how robust system must be and how long you intend to keep it
running as it is.

PCs are sporting tons of RAM and HD space which is great for
logging etc. Thanks to nicer screens they are often also visualy
more apealing and can have more information on same screen.

Problem with PC is complexity of both hardware and software.
PC was never meant to be stable workhouse for mission critical
applications. If downtime is not an issue you can consider it.
PLCs on other hand don't have vanila sound cards integrated
on controller board, no registry and loads of DLLs. They are
lean mean machines designed for one specific task,
not to be home entertainmen center running 3D games, Excell
and MS Strits and Trips. You turn it on, and it works right away
(one or two second boot time). If something is not working,
pull it out and insert replacement card. Thats usually it.

If you have PC component fail, good luck finding EXACTLY same type
so you don't have to remove old drivers and install new ones.
Try to find spare motherboard or CPU (must be SAME!!!) for PC you
bought 8 years ago. Even if it's 6 months old you are likely to have
trouble finding SAME part. There are similar newer parts of course,
but they cannot be simply exchanged without loading new set of
drivers like if you swithc from ATI to NVIDIA card for example.
And even if you do this, chances are you have to go to internet to
get latest and hopefully more stable drivers than ones you got on CD.
All of this cost time (lots of time...)

With PLC it's other story. Call your local rep for spare PLC card and
no problem. You are getting same thing even if it is dusty. Just read
how many topics here are still about PLC5 (Allen Bradley) and A2A or
A3A (Mitsubishi) just to name some.

You can check PC forums and find that someone still runs DOS 5.0 on
some 386 with 2Mb of RAM. But that's just few lonely geeks without
girlfriend, dog or kids.

When we talk about PLCs this old, industry is still running on it.
And to replace PLC card, it's not big deal for any electrician
(you find those guys in every plant). And if there is a problem,
you still can call tech support. To replace some PC component,
reload software written by some crazy guy who is not in town, you
might get lucky on occasion but chances are you will be paying dearly
and cursing the day he was born if something goes wrong. Good luck
calling Microsoft when your hardware is not recognized or supported
by Win2006, Win2007 or WinNG (Next Generation).
 
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Holy Cow...this is so familiar that I wouldn't be surprised if you told me that you work in the Peoria area.

PLC definitely!!!

First, let me say that I am not a fan of PC control.

I have used GE Cimplicity PC based control on a Engine / Generator / Switchgear / Load Shedding project and it had not had any problems. It was primarily for data acquisition and remote control. I did have several Fanuc 9030's in there also, along with a slug of GE MultiLin relays/controllers. The 9030's would start the standby generator, control the switchgear, and load shed through the MultiLins by themselves in the PC('s) were down. The GE people said to be careful on computer selection. They used Dell for all factory projects at the time, and also recommended Micron. The factory boys said to avoid HP and Compaq, that the GE software would crash regularly. This was in 98, so some things may have changed.

I had Steeplechase PC controller software forced on me once. Machine Builder could never get it to run smoothly, and customer decided not to use a million dollar machine. Before it was built, I mentioned for $3,000 that a complete GE 9030 could be installed, which was considerably less than the PC and software. Eventually, a new Plant Manager came in, the two robots were set up to run independently, and three micro PLC's ran the rest of the machine. Perhaps the problem was the PC's being used. This is one experience with Steeplechase, but for the expense involved, and other stuff listed on previous posts, I recommend PLC way over PC.

The Diesel Engine Generator control industry has always had a love for ice cube relays. A mechanic with NO electrical background can troubleshot them easily, and make repairs easily. Back in 72, several of us employees designed prototypes of solid state engine starting panels for the "Peoria Switchgear Leader" at that time to evaluate. It didn't go anywhere then. A couple of years later, two of our group were making pc board base autostart panels, but the times were just incorporated onto the board, and the ice cubes plugged onto it also, as opposed to seperate sockets. By the mid-eighties several solid state controls were out, but one fact remains, they will still have relays at least to control the fual valves, rack solenoids and starter motor contactors.

PLC will be best for your application. In event of a power failure, the PLC can reset and start the engine quickly. (Though not as quick as the standard 7 relays, four lights, and two timers in the oldstyle cranking panel) With load sharing, peak shaving, parallelling, etc you can't trust that the a PC won't belch at the wrong momment, and put everyone in the dark, and leave them there. PLC's will be more forgiving the the electrical noise and otherwise harsh environment where a genset is located. You should see the electrical spikes on an oscilloscope when three CAT 3600 series decide to start.

Locomotives run with embedded controllers, basically, just a type of PLC running a 6000 hp genset with 6 1000hp motors on steel wheels works fairly well.

Should you need to look for a job in a year or two, PLC's will be a little easier to find something with. If at all possible, have your employer get you some Allen Bradley training, you can use it almost anywhere. I wouldn't be surprised if your company is using a lot of GE Fanuc (My Favorite). GE is nowhere as popular as A-B, but once you are familiar with it, you should find that it has more capabilities and easier to program.

I started at REDCO in Peoria in 72, I would be interested to hear where you are at (though I have a good guess).

Best Regards.....casey
 
I do not know if the generator system is emergency power or base load or co-generation. Does not really matter. Generator controls are a major part of my business. Emergency power, power stations, co-generation, heat recovery etc etc

1. Always use PLCs on batteries, preferably 2 battery sets and chargers through combining diodes for redundancy.

2. A sliding switch to allow disconnection of 1 battery bank for load testing on a regular basis to determine battery condition.

3. My preference is Omron but any PLC will do. Normally use the Omron CJ1, vast numbers of analogues possible, lots of local and remote I/O via Device Net or Omron Compo Bus S, dependant on the processor chosen.

4. A HMI attached to the PLC will give you a certain amount of trending but is quite limited. Good for running trends but not archiving, although the new Omron NS screens have provision for memory cards that can be written to and removed for extraction of data to a computer on a regular basis. Other HMIs also offer this feature.

5. PLCs are not the place to do trending, except very short term. Takes up too much memory and slows the scan considerably.

6. For trending, strongly suggest Citect. All SCADA systems have trending available but I consider Citect the best.

7. If Citect is out of the price range, have a look at Omron CX-Supervisor. Unlimited tags, works directly with Omron PLCs or via OPC to all other devices, can use internal scripting language or VB - your choice, is very powerfull and inexpensive.

8. I would not trust ANY critical type process to Mr Gates. If Windows crashes, soft PLC runs underneath and continues to operate - UNTIL windows requires a power down, or the power supply in the PC fails etc etc.

9. If you are considering using a PC, have a look at the Omron CS1 PLC on a PCI card. Requires a separate 24VDC power supply to it. If the computer packs it in, the PLC continues to run on the 24VDC power supply, even out of the computer. Works with remote I/O. It is a real PLC.

I do not know of any others that work this way but I am sure they are around.
 
awilken,
your application looks like a "normal" one for a "normal" PLC.
You should study ladder programming. Its easy to get into and is the closest to being a "standard" in this area (mind you, there are little differences from vendor to vendor).

And I aggree with everybody else, that it would be easiest for you to split the job in the "normal" way:
Control, interlocks ... PLC.
Alarming, datalogging, trending, visualisation ... HMI.

edit: For the HMI, if no other reason dictates it, use a standard industrial operator panel, preferably from the same vendor as the PLC. Dont use a PC.
 
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PLC's Win

Thank You for all the great comments. I am no longer at the fork in the road. I will take the path of PLC's, without a doubt. Now education is the next step.

I wonder how long it will take to learn a fair amount of PLC's programming? If you were me. " Knowing what you know now" Where would you START? What would you do different?

A little back ground 8 years Marine Electrial, 9 years Prime and Stand-by generator Tech, 3 years Instructor for generator and electronic controlled engines.

Tons of troubleshooting and reading wiring prints. Never Designed or Programmed

To Casey! Let just say I have been to Peoria several times. Big Al's is a club where every girl in there wants you! he,he,he. I love to each at Famous Daves, I would never swim in the Peoria River and the River Boat Casino took my money.

I have worked on several of the Reco engine start panels back when the ice cube relay were imbeded in the PC cards "Always had 2 spare cards on the truck, The solder runs on the back of the cards would burn-out for some reason. Let's just say I see YELLOW and Not Dog but ??? If you would like, we can stay in contact, that is if you wouldn't mind helping with my career change. I need all the help I can get!!!!!

Once again thanks and I hope I can get to a level to help others who need help!!!!

Regards,
awilken
 
PLC Training

There are two paths to take for formal training in PLCs.

1. Check with your local TAFE (I think you guys call them community Colleges) they run intro courses.

2. Get in touch with the distrubter of the brand of PLC you wish to use and enquire about their training courses.

In Australia a combination of the two options is best starting with the TAFE courses which give you a more generic into into PLCs ( and over here anyway are very cheap AU$1 per hour). Once you have completed these courses do the manufactures cource. These tend to be more technical and take you through the PLC's higher functions and manufacturers recommended way of doing things.
 
For starters, press the "Learn PLCs" button at the top of the page. This will give you a good start.

Here is an excellent link to learn PLCs. It is based on an Omron shoebox type PLC. You can learn a lot from here on basic PLCs, this one is fairly basic without a lot of the high end functions available today.
Learn Basic PLC

If yiu wish to travel the AB route, here is a link but the information covers far more than basic concepts
Hugh Jack's PLC Book

These sites will give you an idea what you are in for.

By the way, I have no formal training in PLCs but have learned along the way. Have programmed up to base load diesel generator power stations, several of them now. Also learned SCADA systems myself after a quick 2 day course on Wizcon. It is much harder to do this now. Most employers want a piece of paper.

Good luck.
 
awilken:

REDCO and many of the companies that were started by former Redco employes bought most of their PC board products (timers, diode boards, relay sockers) from the same company for decades. If you figure the physical size of the pc runs, compared to wire size, some of them were 18-24 gauge. The inrush current of a stater solenoid or rack solenoid would easily smoke many sockets. The panels were checked with a test light, and often didn't get the "real load" until the first startup in the field.

In Peoria, there has been a dozen or more engine control shops in operation simultaneously at several points in time. You could usually tell looking insude a panel where the designer got most of his experience, by the components used. A couple of guys I worked with built timers, relay sockets, and whole cranking panels on a single board, but they all went out of business after a year or two.

PLC Training -

The traing offered on this site is good. You will find some good info on a google search for "free plc training" in the 615,000 search results. Received two catalogs in mail yesterday, with a lot of programming info in them. I would suggest getting your own library of catalogs, many manufacturers have interactive demo and training programms on their adertising CD's.

Somewhere (I thought on this site, but maybe it was another PLC site) had a link of manufactures. Anyway, notice the brands mention on the posts here, and look into them.

AutoCad -

If you never did it, it is a valuable asset to get. Granted, a $4,500 program for simple schematics is a bit much. Big Yellow is using a PRO-E offshoot, that is probably $65k. If you have not used autocad, a lot of books available from interlibrary loan. An old autocad LT program can be had cheap on eBay.

Misc -

Engine controls are addictive. I don't know why. Hard to get out of your system. I know guys that have been in and out of it many times the last 30+ years. PLC's are the same way, only worse. Once you start playing with them.... Someone stated on a post a while back:

"Betcha can program just one"

Will PM you when I have some free time to see how it is going...

casey
 
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kc9ih said:
Somewhere (I thought on this site, but maybe it was another PLC site) had a link of manufactures.

You thought right... Phil's manufacturer links are HERE.

The link is only accessible from the "Learn PLCs" pages. IOW, you can't get there from here... ;)

beerchug

-Eric
 

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