You are not registered yet. Please click here to register!


 
 
plc storereviewsdownloads
This board is for PLC Related Q&A ONLY. Please DON'T use it for advertising, etc.
 
Try our online PLC Simulator- FREE.  Click here now to try it.

New Here? Please read this important info!!!


Go Back   PLCS.net - Interactive Q & A > PLCS.net - Interactive Q & A > LIVE PLC Questions And Answers

Reply
 
Thread Tools Display Modes
Old February 13th, 2020, 03:40 PM   #31
Ron Beaufort
Lifetime Supporting Member
United States

Ron Beaufort is offline
 
Ron Beaufort's Avatar
 
Join Date: Jul 2002
Location: Charleston, SC
Posts: 5,631
I've always had a question about something - but then I asked a couple of students from Chile (they said that they used the metric system down there) ...

when you go to Lowes or Home Depot (or whatever happens to be the overseas version of a lumber yard) do you ask for a two-by-four (in inches) or maybe a 5.08-by-10.16 (in centimeters) ? ...

according to Hector and Pedro - in Chile you ask for a two-by-four ...

and incidentally - a two-by-four isn't really a full two inches by a full four inches anyway ...
__________________

2-B ?
Best regards, ----+----] [----+------------( )----
Ron | |
PLC Training Boot Camp - Retired | 2-B |
+----]/[----+

I once was lost, but now am found, was blind, but now I see.

  Reply With Quote
Old February 13th, 2020, 04:13 PM   #32
janner_10
Lifetime Supporting Member
United Kingdom

janner_10 is offline
 
Join Date: Dec 2014
Location: Tewkesbury
Posts: 1,063
Depending on your age, you can ask for 2" x 2" or 50 x 50, most places work in both, but predominantly metric now. Bizarrely, the length is always metric.

The old imperial system hasn't been taught since the early 70's, so it's an age thing. My Dad is 70 and just can't shake imperial measures, I'm 45 and really have to think when he describes things in feet and pounds. My nephew is 25, hasn't got a clue what he's waffling about!

All of Europe has gone full on metric, the UK is stuck at 80%, why, I really couldn't say.
  Reply With Quote
Old February 13th, 2020, 06:49 PM   #33
Tom Jenkins
Lifetime Supporting Member
United States

Tom Jenkins is offline
 
Tom Jenkins's Avatar
 
Join Date: Apr 2002
Location: Milwaukee, WI
Posts: 6,079
I remember about 40 years ago when I had to make a presentation to a group of Japanese engineers. I converted all my graphs to official SI units. About halfway through the presentation one of the Japanese engineers slowly raised his hand and asked, "Please sir, what is a Pascal?".

I pulled out my US Customary Unit transparencies. Smiles and nods all around.

I've had similar experiences in Canada and Europe. The moral: go with what the end user is comfortable with, and SI be d$%@#$ed.
  Reply With Quote
Old February 13th, 2020, 08:08 PM   #34
janner_10
Lifetime Supporting Member
United Kingdom

janner_10 is offline
 
Join Date: Dec 2014
Location: Tewkesbury
Posts: 1,063
Quote:
Originally Posted by Tom Jenkins View Post
40 years ago .
I see your problem.
  Reply With Quote
Old February 13th, 2020, 08:14 PM   #35
drbitboy
Lifetime Supporting Member
United States

drbitboy is offline
 
drbitboy's Avatar
 
Join Date: Dec 2019
Location: Rochester, NY
Posts: 1,355
Wink

Quote:
Originally Posted by janner_10 View Post
I see your problem.
I can see yours.
  Reply With Quote
Old February 13th, 2020, 08:43 PM   #36
theColonel26
Lifetime Supporting Member
United States

theColonel26 is offline
 
theColonel26's Avatar
 
Join Date: Feb 2014
Location: West Michigan
Posts: 420
Quote:
Originally Posted by AustralIan View Post
"In most other PLCs" and also the IEC 61131-3 standard.
Huh?

Are you agreeing with me OR are saying that the IEC-61131-3 calls it XIC and XIO?
__________________
SkyCad is by far the Best ECAD Schematic Software I have used.


Fact my "Fun Facts" are never fun
  Reply With Quote
Old February 14th, 2020, 02:43 AM   #37
JesperMP
Lifetime Supporting Member + Moderator
Denmark

JesperMP is offline
 
JesperMP's Avatar
 
Join Date: Feb 2003
Location: Copenhagen.
Posts: 14,382
Back on topic, I think that XIC and XIO are better terms than N.O. and N.C.
The "normal" is open for interpretation, and "closed/open" for power can flow/cannot flow is counterintuitive.
So if the XIC and XIO are prevalent in north America, then I have to hand it to you that you have us beat.
But who is to BLAME for the "N.O." and "N.C." ? That is the important question that needs answered.
Since N.O. and N.C. are english termns, and if they are not from north America, then it must be the british or the australians !!
In danish and german the N.O. and N.C. are not used. We call them "closing-contacts" and "opening-contacts" respectively.

edit: It just dawned on me that the "closing" and "opening" in german is exactly the the same as problem as in the N.O. and N.C.
So it must be the germans who did it ! Cant be the danes because the exact translation from the danish terms are "closing-contacts" and "breaking-contacts".

edit again.: Hang on hang on. "eXamine If Closed". With closed meaning power can flow. It is the same again. Now I believe it is the US who did it.
__________________
Jesper
See my profile interests for Q&A

Last edited by JesperMP; February 14th, 2020 at 02:56 AM.
  Reply With Quote
Old February 14th, 2020, 05:21 AM   #38
ivo.maenen
Member
Belgium

ivo.maenen is offline
 
ivo.maenen's Avatar
 
Join Date: Nov 2003
Posts: 663
Quote:
Originally Posted by JesperMP View Post
But who is to BLAME for the "N.O." and "N.C." ? That is the important question that needs answered.




Who wrote the first software for 'ladder'-programmation?
__________________
Assumptio mater errorum est.
  Reply With Quote
Old February 14th, 2020, 09:07 AM   #39
dogleg43
Member
United States

dogleg43 is offline
 
Join Date: Dec 2005
Location: Indiana
Posts: 420
Quote:
Originally Posted by ivo.maenen View Post
Who wrote the first software for 'ladder'-programmation?
Possibly Dick Morley, who invened the first PLC.
  Reply With Quote
Old February 14th, 2020, 09:17 AM   #40
dmargineau
Lifetime Supporting Member
United States

dmargineau is offline
 
dmargineau's Avatar
 
Join Date: Dec 2011
Location: Midwest
Posts: 2,507
1968 General Motors -Bedford MA US...The brand is still around: MODICON (Modular Digital Controller)...It is currently owned by (French) Schneider Electric...Go figures......
  Reply With Quote
Old February 14th, 2020, 10:00 AM   #41
Tom Jenkins
Lifetime Supporting Member
United States

Tom Jenkins is offline
 
Tom Jenkins's Avatar
 
Join Date: Apr 2002
Location: Milwaukee, WI
Posts: 6,079
Quote:
Originally Posted by janner_10 View Post
I see your problem.


"Those who do not learn history are doomed to repeat it."

George Santayana

  Reply With Quote
Old February 14th, 2020, 10:59 AM   #42
AustralIan
Member
Germany

AustralIan is offline
 
Join Date: Jan 2013
Location: Germany
Posts: 1,161
Quote:
Originally Posted by theColonel26 View Post
Huh?

Are you agreeing with me OR are saying that the IEC-61131-3 calls it XIC and XIO?
I am agreeing, and expanding. "Most all use NO/NC," which makes sense because "that's what the relevant standard says."
  Reply With Quote
Old February 14th, 2020, 12:49 PM   #43
drbitboy
Lifetime Supporting Member
United States

drbitboy is offline
 
drbitboy's Avatar
 
Join Date: Dec 2019
Location: Rochester, NY
Posts: 1,355
Here's the thing, and I think someone else already expressed this: NO and NC actually mean different things when referring to a physical switch and an instruction on a PLC ladder rung (or ST or FBD or whatever).

The former has been beat to death: O(pen) or C(losed) is the switch state when the coil that drives it is de-energized (I hope I got that right or else maybe I should be beat to death)

On a PLC, O(pen) or C(losed) refers to the switch (bit, really) state that causes the instruction to evaluate to False; the opposite state evaluates to True.

In most cases they are the same, but I could take an input driven by a NO physical switch and apply a NC ("XIO") instruction to that input, and that rung would evaluate True when the physical switch's coil was in it's "normal," de-energized state.

And what about a manual knife switch? There is no "normal" for that, but I could use one to drive an input, and evaluate it with either NO or NC instruction.

I don't think this is exceptionally confusing in principle, but it does make a slight case favoring non-NO/NC phrases, such as XIO/XIC, for clarity in the limited domain of PLC programming, because ultimately it is the actual switch/input state that is of interest to the programmer, and not so much the design choice made by the designer of the physical circuit about what the switch does when its coil is de-energized.

Am I way off base here?

I really hope I didn't flip anything in this boolean rant, but I guess either I did or I didn't.
  Reply With Quote
Old February 14th, 2020, 01:32 PM   #44
Ron Beaufort
Lifetime Supporting Member
United States

Ron Beaufort is offline
 
Ron Beaufort's Avatar
 
Join Date: Jul 2002
Location: Charleston, SC
Posts: 5,631
for anyone who STILL hasn't seen the movie ...

here's a quick preview of the YouTube videos that I recommended way back in Post #2 ...

an XIC instruction ALWAYS does just one simple thing ... it ALWAYS tells the PLC processor to "Go Look for a 1" in a BIT/BOX ...

if the processor finds the 1 that it's looking for - then the processor will nod its little electronic head (yes) - and the XIC instruction will be evaluated as TRUE ...

if the processor does NOT find what it's looking for - then the processor will shake its little electronic head (no) - and the instruction will be evaluated as FALSE ...

on the other hand ...

an XIO instruction ALWAYS does just one simple thing ... it ALWAYS tells the PLC processor to "Go Look for a 0" in a BIT/BOX ...

if the processor finds the 0 that it's looking for - then the processor will nod its little electronic head (yes) - and the XI0 instruction will be evaluated as TRUE ...

if the processor does NOT find what it's looking for - then the processor will shake its little electronic head (no) - and the instruction will be evaluated as FALSE ...

it's all covered in the YouTubes ...
__________________

2-B ?
Best regards, ----+----] [----+------------( )----
Ron | |
PLC Training Boot Camp - Retired | 2-B |
+----]/[----+

I once was lost, but now am found, was blind, but now I see.


Last edited by Ron Beaufort; February 14th, 2020 at 01:34 PM.
  Reply With Quote
Old February 14th, 2020, 02:20 PM   #45
AustralIan
Member
Germany

AustralIan is offline
 
Join Date: Jan 2013
Location: Germany
Posts: 1,161
Quote:
Originally Posted by Ron Beaufort View Post
an XIC instruction...
an XIO instruction...
Agreed! This is how I think of them.
] [ Means "if true"
]/[ Means "if false"
Thinking back on my post, any relation to actual relays is purely academic.
The hardest part is remembering their names.
I guess with IEC61131-3 it's easy: the open one looks more open.
With XIC/XIO just remember their names. They're 3 letters each.
  Reply With Quote
Reply
Jump to Live PLC Question and Answer Forum

Bookmarks


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Topics
Thread Thread Starter Forum Replies Last Post
No & nc kulgauravkanade LIVE PLC Questions And Answers 8 September 22nd, 2015 10:43 AM
TwinCAT 3, NC / Motion, NC control, how to? tevious LIVE PLC Questions And Answers 0 February 20th, 2015 09:39 AM
what are the main differnces between NC & CNC ?? magdyfayad LIVE PLC Questions And Answers 4 October 6th, 2009 04:43 AM
Normally open or closed or... Phil Melore LIVE PLC Questions And Answers 15 February 3rd, 2003 08:14 PM


All times are GMT -4. The time now is 12:54 PM.


.