Talk:Programmable logic controller

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[edit] Programming PLC

There is some info missing: PLC can be programmed not only in ladder languages or C, but there is a galore of possibilities:

  • ladder logic (mentioned),
  • structural languages - mostly C (mentioned),
  • low-level languages- assembler, basic,
  • block languages, like FBD, PD, FUP...,
  • sequential function charts.

However, I don't feel wise enough to write more :D

There seems to be quite a few inaccuacies with this article. For one, complex programs need not always be done by a ELECTRICAL Engineer (It states Industrial Engineer). There are many highly skilled PLC programmers who are not Electrical Engineers. ProdigalSon

Also the IEC-1138 standard is not relevant to the topic, the actual one is IEC-61131-3; but there is no "structured C" there at all.

[edit] History

There seems to be some confusion about the history of the PLC. The present article seems to indicate that GM was the driving force behind the development of the PLC. However, in this article - http://www.barn.org/FILES/historyofplc.html, Dick Morley, its inventor, seemed to have had in mind the machine tool industry when he first envisioned it. Can anyone clarify this issue? Which came first - GM's proposal for a PLC or the PLC itself that neatly fit into GM's needs?

Also: The term PC for 'Programmable Controller' was used until ~1981 with the introduction of the IBM PC. 'PC' then became 'PLC' to differentiate from the ubiquitous Personal Computer...

Also: the article says; "PLC and Programmable Logic Controller are registered trademarks of the Allen-Bradley Company". How can this be? 193.202.109.254 14:38, 25 October 2007 (UTC)


AB has a patent on the "Programmable Logic Controller", abbreviated PLC.

http://www.plcdev.com/allen_bradley_plc_patent_3942158_by_dummermuth

Jharris693 (talk) 15:21, 11 January 2008 (UTC)

[edit] Simple and representative

We don't need to document all methodologies used for each brand of PLC. We all have our favorite system and after a while it seems like the One True Way. I programmed ZWorld controllers in C(more or less) to control gas flows. If you controlled cutting machines using GE Fanucs, everything has a slightly different feel. We don't need to document the different feels in this page. For example, I just whittled down a big mess regarding the labels we use for digital input values: On/Off, 1/0, T/F, 24VDC/0VDC. Any of these is valid. Including them all just confuses the un-initated reader. You control motors, I control valves but we don't need to list everything that is a digital output to communicate the idea of Digital Output. Same with programming languages, UIs, data storage, networking... Can we keep it simple and representative please? -- TomCerul 05:38, 21 July 2005 (UTC)

[edit] Examples

Okay folks, we know PLC programming is full of millions of details regarding how things can go horribly wrong. What examples should we use? My choice has been

1. DI/DO
2. AI/AO
3. Should we add an HMI example?
4. And now I'm thinking we should add an example and section describing the level of the complexity inherent to industrial control/PLC programming. Perhaps:"Now change the controlled fluid to gasoline. Extensive safety precations must be implemented. Overfill, vapor detection, catch pan liquid detector, exhaust monitoring, controller air pressure monitoring..."

I want to make most of the article clear enough for a layman. TomCerul 15:41, 1 September 2005 (UTC)

Since PLCs are never installed without a lot of accompanying electrical interfacing, some pictures of typical electrical control cabinets would help give PLC installations some context.

[edit] External Links

I suggest we establish external links - it may make sense to link to a few manufacturers and other useful non-commercial resources. See Also should refer to other entries in the Wikipedia. If no one has objections I will change link labels and start links to major PLC mfgs - AB, Siemens, Modicon, GE Fanuc, etc. - but would like to est a "policy" so this page does not become a link farm. VGarner 16:53, 5 April 2006 (UTC)

[edit] Communication Protocols

Could someone please comment on what standards for serial and or network communication exist? Thanks.

OK. Spalding 03:04, 15 July 2006 (UTC)

[edit] Trademark

[edit] Newer Methods

I would like comments on newer technology if any is replacing this.

[edit] ============

I notice that Programmable logic controller has chosen to use asterisks to denote that PLC is a registered trademark of Allen-Bradley, and Unix has chosen to use the extended ASCII registered trademark character. I'll let you guys duke it out, but we really shouldn't have two standards.--Superluser 00:35, 19 April 2007 (UTC)

I removed the "®" based on Wikipedia:Manual of Style (trademarks). --Mark @ DailyNetworks talk 02:12, 28 May 2007 (UTC)

I had noticed Siemens and other manufacturers use the term "PLC". I checked with the United States Patent and Trademark Office and searched Allen-Bradley. I did not find PLC or Programmable Logic Controller registered to Allen-Bradley. I did find PLC-2 (registration number 1103007), PLC-3 (registration number 1228339), and PLC-5 (registration number 1709845). --Mark @ DailyNetworks talk 02:28, 28 May 2007 (UTC)

[edit] microprocessors

how they operate and thier functions —Preceding unsigned comment added by 41.220.2.117 (talk) 13:30, 24 November 2007 (UTC)

[edit] Digital and analog signals example

I changed the wording of this example a bit to be more clear. Am I wrong in thinking that it should be two series float switches (a logical AND gate) rather than two parallel float switches (a logical OR gate)? Schreineradam (talk) 15:03, 13 February 2008 (UTC)