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surfman2
May 22nd, 2002, 10:29 PM
Recently one of the corporate engineers did a project at our plant and decided to use Grafset instead of the good old fashion Ladder Logic. My boss has decided that we need to learn Grafset. Anyone know where to go to find info? Thank you.

PS. Please email me at: surfman2@kans.com

Jay Anthony
May 22nd, 2002, 11:38 PM
Try this link:

http://www.lurpa.ens-cachan.fr/grafcet.html

Jim Dungar
May 23rd, 2002, 10:22 AM
Which brand of PLC. There are some basics of Grafcet, but there are usually very many differences. The certified IEC61131-3 versions should be almost identical. I believe only Schneider Electric and Siemens are the only manufacturers that are "certified", the rest are "compliant" which means they can be as unique as they want.

93lt1
May 23rd, 2002, 11:09 AM
Define: Grafcet

surfman2
May 23rd, 2002, 12:00 PM
We are using Allen Bradley PLC5 & SLC500 processors with RSlogix software.

Jim Dungar
May 23rd, 2002, 03:19 PM
Too bad. Good luck.

Allen Nelson
May 23rd, 2002, 03:41 PM
Surfman2: Ok, so you have AB PLCs. But what brand of PLC did the guy do with Grafcet?

The PLC-5 at least supports SFCs, but the SLCs are straight ladder.

To learn something about Grafcet, keep your eye on the State Logic thread.

Jim Dungar: IEC defines 5 PLC languages - Grafcet isn't one of them. SFC is, which some people use synonymously, but isn't quite (I think).

Jim Dungar
May 23rd, 2002, 05:31 PM
Allen,

You are absolutely correct, all Grafcet are SFCs, but all SFCs are not Grafcet. Certified SFCs in IEC61131-3 are very rigidly defined.

Historical Evolution of Grafcet (per Telemecanique)
In 1977, Grafcet was published as a set of standards in France
In 1982, Grafcet was defined as French National Standard number NF C03-190
In 1989, the IEC adopted Grafcet as a standard. The standard refers to Grafcet as Sequential Function Charts.

surfman2
May 24th, 2002, 07:28 AM
He did the Grafset for a PLC 5/40/C. I'm not sure but I think thier was some mention of Powerpoint also.

The top half of the prints have a flow chart. Then there are boxes on the lower that name a piece of equipment and an interger location. In the box also is the list of bits 0-15. Each one has a description. for example:

N7:0/1 Raw Material Auger

.0 E-Stop
.1 Start
.2 Motor Overload
.3 Interlock

And so on. When I look at these verses ladder logic I don't see if it is saying the bit needs to be high or low if the condition is true of false. It seems that XIC and XIO say it plain as day.

Also that page seems to talk about one piece of equipment. It doesn't seem to show what conditions have to be meet before it will operate. With ladder logic it all right there in a rung. Start at the left and read till you get to the OTE, what isn't allowing the path is the problem.

Thank you.

Allen Nelson
May 24th, 2002, 02:11 PM
I just spent my lunch break reaquainting myself with how Rockwell does SFC.

It's odd, but it pretty much follows the rules of SFC.

But I don't understand what you are saying about the "prints".

The way AB does it, the "Action" boxes each have a subroutine of ladder. The outputs (coils) in that subroutine (usually real-world output, although internals) will be handled, epending on how that subroutine was "called" in the SFC (N(on-retentative),S(et),D(elay), etc). An action block can call multiple subroutines, with different.

The "Transition" boxes are also subroutine calls to straight ladder. Those subroutines should contain a single rung that has a EOT output. When the EOT goes True, the subroutine called by the Action box is no longer scanned (Again, the state of the outputswill be determined on how they were called).

When I generated a report, I saw only SFC or Ladder - no split pages. You are proably looking at some sore of roadmap to understanding how he set things up (I sounds like he allocated two words for each machines "State", and then assigned a bit for each state - N7:0/0=RM Auger E-Stop, N7:0/1=RM Auger Start, etc. Sounds like a reasonable approach.

I suggest, as a starting point, that you forget the printouts (and Powerpoint? Someone loaded a Powerpoint preentation into a PLC? That I've got to see!!), and open up the program (offline at first) with RSLogix. And download the PLC-5 Instruction Set manual from AB.com - there's an enire appendix devoted to SFCs.

If you have any specific questions, or if you can post what you are looking at, I'll try to help some more.

Gerry
May 24th, 2002, 06:19 PM
I think I recognise what surfman's talking about here. I've known people to draw every portion of a control system as a SFC using powerpoint and then translate those charts into ladder using the 'classic?' technique mentioned in that other lengthy thread.

It's a methodology that is readily transportable across brands and models. However, to persist in using it on a PLC that has such (in my opinion) excellent support of SFC's built in seems a waste. There is one minor plus for the method in that it enables on-line editing of the 'chart'.

Pierre
May 24th, 2002, 07:46 PM
Gerry said;

-I've known people to draw every portion of a control system as a SFC using powerpoint

-It's a methodology that is readily transportable across brands and models.

Well, I've got to admit to this one, altough writing on a piece of paper would qualify in the same quategorie of ease for porting to other brands;) ;) ;) ;) ;) ;)