Let's get philosophical: Which PLC to use?

[Gerry]

don't let all these A/B boys run you over.

It's a veritable traffic jam, isn't it.

Anyway, you might want to consider this.
It may just suit your needs.

 

[Gerry]

correction

The correct link

I got it wrong the first time

 

[PhilipW]

Thank you Peter for once again getting our minds out of petty brand rivalries and taking the time to show us some real control info.

I make a point of only answering questions about AB gear because I know something, but surely not everything, about them.

My knowledge of other brands is less and NOT up to date....therefore I strive not to make a fool of myself by slagging them off.

So I always smirk a little (how unpleasant of me ;-) when someone tells us that the now 15 year old SLC500 design, or 25 year old PLC5 systems don't match up to the latest processors and software from their competitors.

Point 1. Yes there is a lot of older generation AB around, PLC2,3, 5 and mountains of SLC500... and much of this installed base is 10-30 years old. Now I suggest that if AD or Omron had a similar sized installed base of technology that old, many folks would also love to tell us all about how inadequate it was .

Point 2. The current generation of Rockwell controller is ControlLogix. It comes in a wide range of forms and prices. The link that Gerry gave is instructive.

Point 3. Some 8 years ago Rockwell NZ lost a significant order to a major industry that we had really chased hard. Over 100 PLC5/40 sized systems were involved.

We lost the job on price to a lower cost competitor. Now just 8 years later the entire system is being replaced. At the outset they had mislead the client about their communications capability. Now just 10 years later the vendor cannot support the product..at all...no parts, no service, no Windows software, no OPC drivers...no nothing. The cost of replacing the hardware is now only a SMALL fraction of the cost of re-engineering the system.

I humbly suggest this customer now understands that the initial purchase cost is not the total cost of ownership.

 

[MikeW]

Still doing research/ finishing up the machine design on which system I will be getting deeply involved with shortly. AD still looks to be equivalent to a Siemens for less money ($10k vs. $18k) and the only way the DeltaV will compete is if takes considerable less programming time as it will runs around $24k for hardware and software.

Peter,

FYI unless I'm misreading the manual, the AD PID function appears to support both Position and Velocity forms of the basic PID equation, look around page 8-30 of AD user manual.

 

[rsdoran]

My 2 cents

First and foremost lets dont forget that the AD stuff was brand labeled by TI and Siemens...its still the same stuff. The 305 etc at one time were a mainstay.

Y'all know I aint the sharpest knife in this drawer of programmers. I would be a total amateur compared to many of you. I can get the job done even though I have problems expressing things to others.

MIKEW this is my OPINION and mine alone, we all know about OPINIONS...
I dealt with S7 300/400 and Simatic S7 software (still have it and adapter) on a regular basis at my job in TN. I think Siemens has some great support people in Johnson City TN and thru their distributors (depending on area). Overall I think the S7 is a good product.
BUT
If I was starting from scratch, cost aside, and had to go thru a learning curve with software...AD would be the choice especially if you dealt with TISOFT etc in the past.

I can not advise on the PID issue but I am willing to bet if you go high end AD it can compare there with just about any brand.

NOTE: This is just my opinion. I think the Siemens S7 line has an abundance of potential. I wish I had the opportunity to learn and work with more than I do. I just think that a person that has dealt with older TI/Siemens will find the AD stuff easier to understand and work with in a shorter learning curve.

As far as background goes I have probably dealt with PLC's many of you have never heard of or seen. I totally despise having to use DOS now because of some of those brands, especially ABB...yeah 2 B's. I also dont have any great affection for GE but the programming style is similar to AD. You may want to look at Horner products too http://www.heapg.com. They offer a line of plc/hmi all in one with free software, Paul Horner is always willing to assist, on site if needed. They have built for GE for years but kind of new with this line of plc's. At least you dont have to type in that dang % symbol with CScape. It can be networked using CAN or DeviceNet. I recently worked at a plant that was the beta site for this line.

I will not praise or bash AB, they have a good product, the new 5000 line may the best there is out there overall...I can not state that as a known fact tho.

I have not dealt alot with OMRON. I built CNC burning machines several years ago and thought they were **** (C200H I think) but have learned they NOW have options others do not have.

For what its worth there is my 2 cents worth. This is from a guy that wears steel toed boots and crawls under machines alot, so add it to the collection of comments and see what you come up with.

Good luck in your new position.

 

[Kevin Hammond]

Mike,

Looks like I'm a little late getting in on this thread. Sorry, been out on the road a lot lately fixing those blasted Automation Direct PLCs......... Just kidding. Well, not in the last few weeks anyway.

I have lots of experience with Siemens S7-300, and AD 205 and 305. My personal preference is Siemens and here's why:

Hardware:
First, I should explain that my stuff goes on railroad equipment, and sees extremes in temperature, shock, and vibration. It's safe to say that they occasionally are operated outside of their manufacturers' environmental ratings.
AD - We have replaced lots of AD 205 cpus, i/o, and bases. The AD 305 stuff has been better, but the vibration has its way with the snap-in modules.
Siemens - No failures yet. :nodi:

Software:
AD - I have never had training on the AD stuff, and it was easy enough to pick up and start programming ladder. I have only used AD on small, fairly simple machines.

Siemens- Can you buy a copy of Step 7, sit down, and start programming? It would be a challenge. But, a little training with a distributor can get you up and running in a couple of hours. I have had two Step 7 classes, and feel very comfortable with it. It's really no more difficult than the other guy's, it's just different.

Ladder, STL, FBD - pick whichever language best fits the task at hand - even within the same program. When it comes to math functions, STL is a gift from the gods. If you have done assembly programming, or have an HP calculator, STL is an absolute breeze. I tend to do my on/off logic with ladder, and arithmetic with STL.

If you need any remote I/O, profibus is fast, and it's a breeze to set up in Step 7. Just drag and drop. This was a major factor in my choosing Siemens.

Support:
AD - free phone support

Siemens - free phone support, plus a great local distributor (In my town, anyway)

In summary, at least talk to your Siemens distributor - and your AB distributor for that matter. This forum is a great place to get opinions, but I would caution you against making a purchasing decision based solely on what you read here (including this post). You are the one who is going to have to live with your decision.

 

[APB]

The right PLC is the one you are comfortable with. If you have worked with 15 languages in 25 years then you will be able to adapt to yet another piece of software. I’m an AD fan, if only because of my budget, good manuals, and fast delivery. Each product has its place. I will use whatever the customer likes, as long as he sends me a PO.

Give some thought to what you will be using these product for in the future. It is likely you will not want more than one brand in your plant so think ahead.

Your loops are going to have to work very quickly. Check that the mechanical response time of the various components is up to the job. Can your loops tolerate overshoot or do they have to be overdamped?

I have had good luck with the 400 series product, but have never had a loop that requires that fast a response. As for speed, you can set the PID loops to operate separately from the ladder program.

There is also a separate module with its own loop controller.

Buy the fastest system you can afford. I like my update rates to be 50 times the time constant of the system. I can always give back computing power, but I can not get more.

I have not always had good luck with auto tuning. I end up using them as starting points and using some of the oldtimers methods. The AD manual (available for free online) has a discussion of the various methods.

You may need to look at more than a PID loop. The plastics hot runner nozzle market uses PIDD (the next derivative). This allows them to respond very quickly to step changes in temperature. They can not tolerate overshooting the target.

Good luck, it sounds like a fun project.

 

[Eric Nelson]

There is also a separate module with its own loop controller.

And I just used two of these 4LTC modules for the first time on that blow molder project. Very simple to set up! What's really nice is that they continue to work even when the PLC is not in RUN mode!...

beerchug

-Eric

 

[elevmike]

A few years ago I took my 5 year old son to Toys R Us for his birthday and told him he could pick out anything he liked within a $50.00 price range. At first he was real excited, but after a while he got overwhelmed with too much data to process, and could not disseminate it all to make a decision that he knew he would be happy with in the long run. This brought him to tears, and we finally left the store without one single item.banghead I went back later and bought him a gift, wrapped it, and he was very happy.

I think this thread is headed in the same direction.

 

[kamenges]

Good one, Mike.
In our zeal to toss out information we do tend to throw out alot of stuff, relevent or not. But that's part of the fun.

BTW, I think you son was trying to 'digest' the information, not 'disseminate' it. That is, unless, he was trying to explain to you what he had learned about each item and why it would be the right choice. And you're right. My sone would go into absolute brain-lock going into a dedicated toy store. WalMart is usually too much for him. I guess he has his old man's lack of focus.

Keith

 

[elevmike]

Keth,

I forgot to mention that I spent 2 1/2 hours picking the gift, and busted the budget! But that's ok because I have lots of fun playing with his new toys. :nodi:

Mike

 

[TimothyMoulder]

It's all about scope...

f I took my two kids into toys-r-us and asked them what they wanted, the answer would be swift and unanimous :

"All of them!"

TM