Talk:Ladder logic
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The analogy between logical propositions and relay contact status is due to Shannon I would say Mr. Bool (Boolean algebra) plus Mr. de Morgan (de Morgan's laws) would be here more appropriate.
...I put in a few extra details and had a bit of a hack around- let me know if you want me to expand it some more - Scampiandchips
Contents |
[edit] if you want...
...I could take some screen shots of your logic as implemented in Rockwell programming software and post 'em here...
[edit] nand?
is this
---[\]---[\]---
X Y
really X NAND Y ?
isn't it (NOT X) AND (NOT Y) which actually means X NOR Y?
Yes, you're right. Fixed.
[edit] standard contact symbols?
The article currently has a mix of contact symbols:
--[ ]--
X
--| |--
Y
--][-- Z
They all mean the same thing, right?
Should we standardize on one type ? The --| |-- seems least likely to interfere with Wikipedia formatting (so we don't need <nowiki></nowiki> tags).
(Note that the --( )-- "coil symbol" at the right of the rung is *supposed* to look different -- it does mean something different).
--DavidCary 18:06, 25 Jun 2005 (UTC)
Agreed - I'll admit I was a bit confused by all the different symbols to begin with.--Rehnn83 14:10, 22 September 2006 (UTC)
[edit] Normally Open COIL?
What the heck does this mean? A coil is just an electomagnet. It can have contacts that are NO or NC but it can't be either. right? TomCerul 18:11, 3 August 2005 (UTC)
- This is probably better called a "not" coil - if a not coil is energized by a rung, its normally-open contacts are open and its normally-closed contacts are closed (a regular coil will have NO closing and NC opening). I ran across this on a Reliance Automate 35, where it was extensively used to save memory - though it made the resulting programs very hard to read (especially so as there was no documentation or variable names displayed by the programming panel that could have alerted you to the weirdness). I had to write my own documentation software for that machine as we only had the one and the manufacturer didn't support anything better. I'll see if I can fix the text in the article. --Wtshymanski 17:41, 4 August 2005 (UTC)
- I agree, it's a NOT coil. The proper use of NOT coils arises from the concept of "failsafe". One example is in machine tools. There is a circuit called an E-STOP string. All of the safety elements on the machine will have a set of NC contacts and be wired in series. The hydraulic pressure is NOT too low. The safety gates are NOT open. The drawbar that holds the cutter is NOT loose. If NO contacts were used, the control wouldn't be able to tell if a wire in the string were broken. In the old days, the string would control a relay. The output of that relay would go immediatly to another relay to be negated. Seán 03:51, 13 March 2006 (UTC)
