Urgent help needed. What makes a PLC a PLC?

[mrdegold]

my two cents

Well I am the customer in the plant and I would have to think that I am the one who decides what is and is not a PLC in my plant. I agree with Vetteboy and can easily see the advantage of maintaining the same equipment. My plant is all SLC’s except for one PLC 5 (which has been here longer than me) I would defiantly pay the up charge for the SLC. To keep everything consistence. It has been my experience that
1) The Startup guy is gone when the real troubles come
2) It will save me money in the long run because I will not need to spend time trying to figure out the differences in ladder languages when it breaks in a year or two and I got to get it running by morning
3) No need for a specialty “Relay/PLC” in inventory for years when as a SLC the inventory already exists and is move more often.
I started using these Mollers Easy Cubes a few years ago and found them to be a great pinch hitter for specialty relays (i.e. timing relays or multicontrol relays) and I even have one still running in on of our air compressors. But If I had to replace the control system for the compressor I would use an SLC for sure

 

[Pierre]

Re: my two cents

I would defiantly pay the up charge for the SLC. To keep everything consistence.

This is smart.

It works until an accountant starts running the plant.

 

[Foghorn22]

As a controls engineer in an industrial plant, I can relate to your customer's situation. My suggestion is to be more interested in what he NEEDS rather than in technicalities about the equipment.

The problem with having different programmable devices is primarily one of support - spare parts, programming software (or hardware), knowledge of the "language" needed, etc. Initial cost is less significant. This involves their engineering/technical staff as well as maintenance electricians. Us industrial end-users would go nuts if we had to keep up with all the different devices vendors try to send us. We have often required our vendors to change out the PLC or other programmable devices to products we customarily use. More and more suppliers are getting the message and designing for several different PLC's up front.

So maybe it boils down to this: if the "programmable rely" is something that YOU (the vendor) will maintain for him (ie, he will never have to do anything except turn this device ON) then he really shouldn't care what it is. If it breaks, he buys another one from you. But if he WILL possibly need to modify or troubleshoot its program 5 years from now, then you should give him his PLC - his people will know how to work with it. If cost is an issue, then maybe that can be negotiated...

 

[ArikBY]

Hy Guys

Excuse me for my language its small ****ing smart relay.
How you can comper SLC with PICO or ZEN ....?
You try to kill a bug with machine gun.

mrdegold

If I am your boss I would expect you to came with creative idea how to save money to the company then to spend money on SLC.
If Pico can do it why I need SLC?
its cheaper to buy one Pico for stock. and to learn about it then to buy SLC for 10 I/O.and in the future to use more of them for simpel APP.
I think this attitude is wrong.
BTW its nice to "fight" with them to get result from this small relay
with there limitation.

 

[g.robert]

Dear gr, you have found a new game. The name of the game is money. We can easaly deduct from you inquiery that you have the contract but do not want to spend the $ for a real-men PLC.

I'll go you one better than that. The system is built, wired, tested and complete. I own the company that builds the panels. My customer builds oil / water separators. A larger company has bought this oil / water separator from them. This is our design and layout. We were indeed giving specs but we all along considered, and still do, that we were using a programmable relay, not a PLC. To compound matters no one from end users staff ever raised concerns from the schematics we submitted prior to building. I should also point out that we have built the exact same system four times, with minor color / certification changes depending on end user's location, for the same large customer.

I need to convince this engineer that this is a programmable relay and not a PLC. This app is a turn-key unit into which they will not interface, program or make any other changes. If they did they would void any waranties that come with unit. If they were to have a problem we could send new programed unit for replacement or even the program on a memory module to be reloaded into existing unit.

While I respect everyones opinion I would really like to hear from those who believe as I do that it is not a PLC. Could you supply any further information to support this belief? Thanks to all that have offered input.

 

[Vetteboy]

You are not using a PLC by my definition. But I'm sure you and I could look at a purple wall and argue out the lilac/mauve thing 'til we collapse. Tell him that the SLC is a "Small Logic Controller" and not a PLC anyway (It is though, really). It's all marketing lingo. Your smart relay is really a very limited Programmable (you program it) Logic (It uses ladder logic from what I've seen) Controller (It controls a few outputs using a few inputs, timers, etc). It sounds like if it's built already and he didn't spec it until now, his maintenance guys can change it to a SLC, or he can be content that it's a "smart relay" and ignore it. If you are building quite a few and he insists on a SLC naturally the price goes up.

 

[gbradley]

What's the first assignment All students get for a PLC?
It's the Traffic signal!
A Pico can control a traffic signal.
Even with a Zebra crossing.

Is a micrologix 1000 with no analog outouts not a PLC? Of course it is a PLC.

Maybe that dog won't hunt, but if it has got four legs and barks, it's still a dog.

 

[rsdoran]

Excuse me for my language its small ****ing smart relay.
How you can comper SLC with PICO or ZEN ....?
You try to kill a bug with machine gun.

mrdegold

If I am your boss I would expect you to came with creative idea how to save money to the company then to spend money on SLC.
If Pico can do it why I need SLC?
its cheaper to buy one Pico for stock. and to learn about it then to buy SLC for 10 I/O.and in the future to use more of them for simpel APP.
I think this attitude is wrong.

Last time I checked AB offered a Micrologix 10 I/O that uses RSLogix500 thats free...if you have RSL500 then it should WORK with it..ie the cost for this ML1000 is roughly $99.00.

Personally I havent seen a so called "smart" or programmable relay that cant be replaced COST EFFECTIVELY with a PLC...depending on brand and software issues that customers require.

Use a MicroLogix1000 that can be programmed with their existing RSLogix500 software and the cost should be same if not LESS to you.

May have to explain that the MicroLogix is a form of SLC but if they are familiar with SLC and have software that they KNOW is compatible will probably be an easy battle.

Note: I am an end user, I am not sure I would buy that explanation. Its hard for US (end users) to buy from OEMS (that withhold programs).

Its between you and the company you contract with on the specifications...if they require something compatible to existing system then attempt to provide it. The step from a programmable relay to a ML1000 isnt that far at a minimal cost,
BUT
If a signed contract did not stipulate it before signed then dont worry about it...unless there is a need to maintain a good relationship.

Personally I dont understand the problem unless you dont have RSL500? Is that is...not willing to spend the money? Using Picosoft 3 and the relay to NOT buy RSL500?

AHHHHH I can relate...I have probably 30K in tools and the same in software/adapters...at some point the investment isnt worth it.

 

[Rick Densing]

The manufacuturer calls it a smart relay, so the end user doesn't have high expectations. In consider it a PLC.

While I respect everyones opinion I would really like to hear from those who believe as I do that it is not a PLC. Could you supply any further information to support this belief? Thanks to all that have offered input.

I think that you are missing the point.

People are trying to convince you that the PLC/not PLC argument will probably not help much. It certainly isn't going to help your image.

Did you already say what you said in that last post to the customer? It is a very good argument on why you would have to charge more. In fact since they did not say anything when your preliminary prints were submitted, I would argue that they don't have much to stand on.

 

[Allen Nelson]

Richard:

Rick's got the right of it. Agruing about whether the EASY is a PLC or not is like arguing about whether a PLC is a computer or not.

- Pro says that it has a processor, an operating system (firmware) and it runs programs.

- Con says that it's very restricted (no Windows, no games), too small of a "hard drive", memory, etc. And the manufacturers don't call it a computer, they call it a "PLC" or a "processer"


It's a pointless argument - both sides are convinced of their rightness and will draw different conclusions from the same set of facts. Not unlike politics....

In arguing over the EASY,

- your customer says that it has a processor, runs ladder, controls I/O

- you say that it's very restricted (rungs are three contacts wide), too small of memory. And the manufacturers don't call it a PLC, they call it a "smart relay".

---

The only way out of this debate is to agree to disagree. If you can convince your client that it is REASONABLE for YOU to call it "not a PLC" (while granting that it is equally reasonable that HE does call it a PLC), then you can get to the negotiations.

If he wants to accept your definition, it will cost what you said it would. If he wants to accept his definition, it will cost X more. (Where X is the added cost of a 4-slot rack, SLC, I/O modules, possibly a larger cabinet, RSLogix, and a small amount of engineering time (fortunaely for him, the logic part of the program is done).

Then it falls on his shoulders whether his principles ("I am right about this") is stronger than his pocketbook (X > $1500).

---

I detect a note of desperation in your tone, that you want to be proven right. What's your problem with selling (not giving) him a SLC? Do you not want to support multiple platforms, and different programming envinorments? That could be the exact same concerns HE has.

Make him understand your pain. Understand his. Save the debates for the forensics team. (No, I don't mean CSI)

 

[Mylo]

Perhaps, I can attack this at an angle you can use..........


My company is an OEM / Machine Builder. (Panel builds)


On one hand We manufacture Purpose built machinery for customers to all their specifications.

When it comes to PLC's we use whatever they specify.Mitsy/Siemens etcetc

If they ask for a different PLC to our usual brands we charge a development fee. i.e. they pay for our software/cables etc. thats just the way it is !

So far clear....

On the other hand we also manufacture "Standard" off the shelve equipment. For this "Standard" equipment we use mitsy PLC's whether our end user is Specified Siemens. the reasoning is that it for us is standard equipment as such does not fall into the category of Machinery specifications!!!!!!!! as for us it's a mass produced item, if the customer wants his made a certain way, theirs large development costs for him to "Customise" our "Standard" product for his needs.................................


Ye see my angle,,



Hope this helps.......



for the record - Don't F#*k about its a goddamn PLC, You program it, in Logic, and it controls stuff!!!!!!!!!

 

[wwtptech]

Can these "smart relays" direct interface with a HMI like Wonderware etc.

 

[kamenges]

Robert-
I think the people telling you to drop the PLC/not PLC argument are correct. You won't win it even though you may be right. It's perception and perception is very difficult to alter.
Turn it into a pure cost/benefit thing for your customer. First off, I assume you have the time and resources to handle these modifications. If not, price it based on contract labor. But your customer has a choice. Take it as is at the agreed-upon price or buck up to money to change to what they want and wait the time you specify. And, no, there is no ethical issue with embelishing either the cost or the time aspect of this. Make sure you emphasize the pain-to-you aspect of this and expect to be paid accordingly.
As you said, the customer had the chance to review the design and didn't object until everything was built. If the customer wants something different now he has to weigh the perceived benefit against WHATEVER COST you choose to specify.

Keith

 

[Stephen Luft]

g.robert,

Unfortunately, you have fallen into the nightmare that haunts many OEMs and Systems Integrators - "customer spec."

From a technical viewpoint, a "smart-relay" is a stripped down version of a micro. It can perform basic functions, has limited I/O, limited program space and limited flexibility.

When a smart-relay takes away business from a micro PLC, one must conclude that it is a PLC.

Personally I don't believe that they are truly PLCs. They don't have serial ports for operator interfaces. There program set is very limited.

The capabilities of the PLC has greatly evolved from a relay/timer/counter replacer in the 70's and 80's to process control. With the capabilities evolving, so too must the definition. PLCs didn't have serial ports to begin with, but with the advent of the PC, you wonder how you did without one.

How do you get around this now, at this moment. Show your customer the literature of the product you are using - http://www.moeller.net/en/industry/switchgear/switch_control/easy/easy.jsp

Explain to them, that it is not a PLC but a "clever control relay" (to quote Moeller)

When an OEM has to support multiple PLC manufacturers just in order to sell to there customers, they increase their costs - across the board, from engineering, to production, to sales.

In a challenging economy, most companies will do what it takes to get a sale. If a customer wants brand Y, they will sell them brand Y. They are concentrating more on the sale, then on the cost of the sale. Some are able to charge their customers for the additional costs, but some aren't.

Our slogan for the last three years has been "thinking outside of the box"

If you truly want to avoid the hassles of customer spec...don't use a PLC. Or use a product that is a PLC but doesn't look like a PLC and don't call it a PLC.

Customer spec is driven by a several factors:

1. Familiarity
2. Experience
3. Preference
4. Ignorance (I'm certain to get a few choice replies for this one)

Hope this helps.

God Bless,

 

[g.robert]

I just wanted to thank everyone for there input (even the guys with the wrong input, HA,HA). The engineers signed off happy to take this unit in leu of multiple separate relays, timers and alternating relays. The deciding factor was that this unit simply replaced relays(yea I know that comment could start the debate all over again)