Question against teachers opinion on book info

[Ron Beaufort]

suggestion: first of all, please be gentle with your instructor ...

then ...

after you and your classmates - and your instructor - have watched all eleven of the YouTube videos mentioned above in this thread - IN NUMBER ORDER - your instructor is welcome to contact me directly if he thinks that a free one-on-one session by telephone might be helpful in making sure that everything is on the right track ... and I promise that I'll be gentle ...

I'm retired from teaching now - but America needs these skills ... I would be happy to provide some extra assistance if necessary ...

TIP: much of the trouble that you're experiencing is the result of using imprecise terminology ... it would be helpful to study definitions (1) through (5) in the following post:

http://www.plctalk.net/qanda/showthread.php?p=537418&postcount=2

note that you should NOT tackle the rest of that particular thread (on FORCES) at this stage of the game ... the figure given at the bottom of that same post might also be helpful ...

I wish you the greatest success in your journey ... and trust me - if you're not enjoying it, then you're doing something wrong ...

stay safe - stay well ...

 

[Tom Jenkins]

Grrrrr...you are reinforcing a bad habit by calling it a "NO" contact.

OG

Most of the PLC world gets along just fine using NO for -] [- and NC for -]/[-

It is really quite simple. The input to the card acts like a relay coil. When voltage is applied to the input it actuates the "relay" and an NO contact closes and an NC contact opens - just like the physical relay it emulates.

 

[Steve Bailey]

What I found when I ran PLC training sessions was that some of the attendees had a hard time understanding the background color change between when the function evaluated true and false. Some of them expected the picture of the NO contact (XIC) to change to a NC contact (XIO) when the state changed. As if the NO contact represented the false state and the NC contact represented the true state.

I wonder if AB could have saved us a lot of misunderstanding if they had named the instructions, XIT and XIF, examine if true and examine if false. Or TFT and TFF, test for true and test for false.

 

[drbitboy]

Most of the PLC world gets along just fine using NO for -] [- ≡ XIC and NC for -]/[- ≡ XIO

That's a really good point.

Like many other fields of endeavor, it's a jargon thing; think of synonyms like trunk and boot, or hood and bonnet, or eraser and rubber, or soda and pop, or sub and hoagie and grinder. Once you grok the jargon, the rest is bookkeeping.

Because sooner or later you and your classmates will run into a non-Allen-Bradley PLC: XIC instruction ≡ NO instruction; XIO instruction ≡ NC instruction; so basically [XI - eXamine If] is the opposite of [N - Normally].

Personally, once I partook of the patient prescription in Preacher Beaufort's pics, I have had zero problems with this (other than the odd brain freeze). A bit is assigned (not set to) a value of either 0 or 1; a rung has a value that is either True or False; XIO/NC or XIC/NO instructions "Look For A [0 or 1]"

So

• the XIC/NO/-] [-/{Look For A 1} instruction evaluates [Output_rung (True or False)] := [Input_rung (True or False)] AND ["Bit Value ≟ 1" (True or False)]
• the XIO/NC/-]/[-/{Look For A 0} instruction evaluates [Output_rung (True or False)] := [Input_rung (True or False)] AND ["Bit Value ≟ 0" (True or False)]

Best of all, that model is not only universal, it's universally accurate (once any jargon is translated), so it comes in extremely handy when diagnosing what others, who work from a faulty model, may consider unexpected or counter-intuitive behavior. And that is where reputations are made.

 

[dogleg43]

Grrrrr...you are reinforcing a bad habit by calling it a "NO" contact.

OG

XIO & XIC has to be two of the most confusing & terrible acronyms of all time.
—-| |—- is NO (XIC)

—-|/|—- is NC (XIO)

Hopefully the OP is learning actual relay hardwiring too so he can properly understand when to use a real normally closed limit switch or real normally open push button, etc. in a PLC wiring scheme.

 

[AlfredoQuintero]

and trust me - if you're not enjoying it, then you're doing something wrong ...

I absolutely find this quote very inspiring. Will start using it in my own trainings. Thanks Ron.

 

[Bit_Bucket_07]

I wonder if AB could have saved us a lot of misunderstanding if they had named the instructions, XIT and XIF, examine if true and examine if false. Or TFT and TFF, test for true and test for false.

I've always thought it unfortunate that AB chose such cryptic names for the NO and NC symbols in their RLL software. TFT and TFF would have made much more sense. I mean, you have to examine either way, NO or NC, in order to determine the state of the associated bit address, so applying a condition to "examination" seems illogical. It's not as if the logic solving will simply ignore the instruction if it's condition for examination is false.

Examine If?

No. Just examine and report back.

Maybe TIE (True If Energized) and TID (True If Deenergized) would have been better?

 

[Mickey]

And if you are still confused read this..See link

http://www.plctalk.net/qanda/showthread.php?t=12334&page=2

 

[jaden]

PLC Ladder (Relay Ladder) language was meant to emulate real relays, therefore Normally Open and Normally Closed are legitimate terms. It is logically consistent, and avoids the long explanations needed to justify the Rockwell terminology.

 

[drbitboy]

And if you are still confused read this..See link

http://www.plctalk.net/qanda/showthread.php?t=12334&page=2

Oh dear, that thread belongs in the "Each individual thinks they are normative and therefore cannot understand why the thing that is obvious to them is not obvious to everyone else" hall of fame.


I like the part where it turns out Dr. Struger is an Austrian, so maybe ESL is the real "culprit" behind the XIO/XIC jargon.


All communication, and implication all learning, occurs via analogy, so we can only work with what the recipient has at the start. Understanding that the world does not revolve around me (oh my!) was when I finally started to understand, and yet I still fall into the trap. Regularly.

 

[Mickey]

Oh dear, that thread belongs in the "Each individual thinks they are normative and therefore cannot understand why the thing that is obvious to them is not obvious to everyone else" hall of fame.


I like the part where it turns out Dr. Struger is an Austrian, so maybe ESL is the real "culprit" behind the XIO/XIC jargon.


All communication, and implication all learning, occurs via analogy, so we can only work with what the recipient has at the start. Understanding that the world does not revolve around me (oh my!) was when I finally started to understand, and yet I still fall into the trap. Regularly.

Yes, the forum does miss Terry Woods.
Terry like Ron (and others here) are very gifted with the written word.

 

[drbitboy]

Huh, I was just looking at the Logix 5000 Instruction Set i.e. here and found this:

​

That has one unconditional test, one conditionally-executed test, and and three statements to describe the intended behavior.

However, that same behavior can be more concisely expressed with but one test and two statements:

​

I.e.

• If the data bit's value is 1, then do eXamine the input rung to get the value to assign to the output rung
• If the data bit's value is 0, then do not eXamine the input rung, and instead assign the constant value False to the output rung

XIO is similar.

It would be more efficient (faster and less code) to implement the second form of the logic, which is described by "XIC/XIO." Perhaps that is the genesis of those acronyms?

 

[cardosocea]

Grrrrr...you are reinforcing a bad habit by calling it a "NO" contact.

Why is it a bad habit? The graphical representation is a Normally Open Contact.
Siemens, OMRON and I'm willing to bet 99% of other manufacturers calls this instruction a Normally Open Contact. Why aren't you wrong instead?

 

[TurpoUrpo]

Rockwell would do a huge favor renaming those to XIT and XIF. Examine if true and examine if false...

 

[geniusintraining]

Yes, the forum does miss Terry Woods.
Terry like Ron (and others here) are very gifted with the written word.

+1

I still want to see Terry's self changing PLC code