One Doubt: Please explain

jamalshahid

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Join Date
Apr 2011
Location
Tennessee
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153
ladder2.gif


I have a simple doubt as i am new to PLC.

what i have understood from this figure. Please correct me if i am wrong.

Before pushing start button. In SW1 we have 0 ( as no current flowing) and SW2 we have 1 ( because contact is closed already)
When we push start button in SW1 we will have 1 ( as current flows) but what will happen in SW2 it will be 1 (still closed) or 0 ( it becomes open)?? please explain( I thought if switch 1 is going to become 1 than sw2 has to become 0) please explain me this doubt.
 
so ...

did you watch those videos? ...

all eleven of them? ...

IN NUMBER ORDER? ...

Jamal, you've been asking many BASIC questions - in MANY threads that you've started ...

those videos will answer all of those questions - in precisely the "step-by-step" - and "beginner level" method - that you keep requesting ...

I say again:

you need to watch those videos ...

all eleven of them ...

IN NUMBER ORDER ...

you're just making this hard on yourself ...
 
Ron your videos are really good. I must say they are very good for the people like me who just started plcs, but in most videos you have one contact (one input max per rung). I have not seen any video( as rt now i am on video 9) that have mutliple inputs.

Please advise!!
 
I am going to look your videos again from start might be i missed something. but please respond to my multiple inputs questions which i raised above.
 
I am looking at them.

excellent! ... we look forward to hearing from you again in about 90 minutes ...

regarding your questions in this thread ...

after you're through with the videos, you should be able to differentiate between:

(1) SW1 – the device in the field ...
(2) SW1 – the XIC instruction in the ladder program ...
(3) SW2 – the device in the field ...
(2) SW3 – the XIO instruction in the ladder program ...

you should also know that your questions cannot be adequately answered based on the limited information you've given – simply because we can't tell now each switch in the field (SW1 and SW2) are electrically wired ... are they wired Normally-Open – or Normally-Closed? ...

and – most importantly - after you're through with the videos, you should be able to answer all of the questions that you've been asking lately for yourself ...

you are in the same boat that many (most?) of my students are in when they first arrive at my classes ...

(a) you have a LOT of misconceptions about what you THINK that you already know ...

(b) you've got a LOT to learn – and what you're lacking is a SYSTEMATIC approach toward learning all of that material ...

the videos will help clear up the misconceptions ... they will also provide you with a SYSTEMATIC approach to learning the basic material (left-to-right as a matter of fact) ...

if you have specific questions about the material in the videos, just note the slide number – and post your question here ... we'll be happy to help ...
 
sw1 is start button and sw2 is stop.if u press sw1 it wont have any effect on sw2,both are independent of each other.

u doubt is very very basic,if u dont understand the videos than read the books,if u want i wil giv u some.also try to understand the NO nc concept, if u dont than u cant do the programming.

if u get the dought still after readingthan feel free to ask.

believe me ladder is very easy it is the begining which is to be understood.

regards,
basharath ali.
 
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please respond to my multiple inputs questions which i raised above.

at the risk of offending you, let me be blunt ...

NO! ...

it took me over four months to produce those videos - and at least two or three nights each week during that time I did not go to bed AT ALL ... instead I caught cat-naps slumped over the computer - and then woke up and worked some more ...

I've already answered your questions (in the videos) ... I have no intention of typing out answers to the same questions that I've already covered ...

I say again:

you need to watch those videos ...

all eleven of them ...

IN NUMBER ORDER ...

you're just making this hard on yourself ...
 
Hi Jamal!
Can you understand an el-scheme of a motor starter circuit?
Your very basic questions makes me wonder.

Perhaps it would be easier for you to understand programming logics if you use FBD instead of LAD?

Kalle
 
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Ron,
Your videos are excellent i must say.

after watching the first 4 videos i understand where i was wrong.

The first thing whenever we are dealing with plcs we have to see our input and output connections. we are dealing with 2 separate inputs/switches (2 inputs) that is SW1 and SW2 and 1 output (Coil or lamp). Before doing anything we know SW1 has 0( because we have seen from connections it is open) and SW2 has 1 (because it is close) in order to make this instruction true or to turn our lamp 0N we need 1 at SW1 because SW2 has already 1 .In order to get 1 on SW1 our contact must close so we need to press the button SW1. SW2 has already 1 we don't have to do anything . When both SW1 and SW2 has 1 our output has 1 and lamp will turn ON.

I hope this is right. Please correct me if i a wrong. Thanks for your vidoes and your help.
 
here is the correction that you asked for ...

OK ... now we're getting somewhere ...

the MISTAKE that you're making now is in considering that:

1 equals TRUE ... and that
0 equals FALSE ...

that is a VERY popular misconception – and it will cause you much confusion if you continue to look at it that way ...

the following is covered in the videos – watch for it and learn ... but here is a preview ...

a BIT is a BOX ... the bit/box can hold either a ONE or a ZERO ...

do NOT (I repeat, do NOT) make things difficult by saying that the bit/box is either TRUE or FALSE ... specifically, bits/boxes are NEVER either TRUE or FALSE ... they just hold either a ONE or a ZERO ...

quick question: have you ever looked at a PLC data table (the bits/boxes) and seen either a "T" for true – or an "F" for false stored there? ...

answer: no, the only thing that you can ever possibly see in a bit/box is either a ONE or a ZERO ... but many people insist on confusing things by describing the bit/box status using the terminology "true" and "false" - instead of ONE and ZERO ...

going further:

again - the following is covered in the videos – watch for it and learn ... but here is a preview ...

XICs and XIOs are INSTRUCTIONS ... regardless of what the official books say, these instructions do NOT "function as an input or storage bit" ... specifically, these are NOT "bits/boxes" ...

now then ... an XIC instruction can be either TRUE – or it can be FALSE ... specifically, it can NOT be a ONE or a ZERO ...

again – watch the videos and you'll see those points made several times ...

summing up ...

(1) in the bit/boxes you have ONEs and ZEROs ... you do NOT have TRUE or FALSE in a bit/box ...

but on the other hand ...

(2) an XIC or XIO instruction can be either TRUE or FALSE ... you do NOT have ONE or ZERO as the result of an instruction ...

I say again:

you need to watch those videos ...

all eleven of them ...

IN NUMBER ORDER ...

but at least now you're FINALLY starting to make real progress ...

party on ...
 
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I can well remember how confused and frustrated I was myself when I first started learning this stuff ...

many of my students meet me at the door on Monday morning already apologizing with something like this:

"Man, I'm your worst nightmare. I've already been to School A – and to School B – and to School C. Now for some reason my boss has decided to send me here. I've tried to learn this stuff – but I can't. I'm too stupid. I'm going to be the worst student you've EVER had."

my reply is usually this:

"No, I (myself) am the worst student I have ever had. Let's see how you feel this afternoon."

invariably the same student will ask me: "You mean it's REALLY this simple?"

yep, but it certainly doesn't seem simple when you don't really know how – or where – to start ...

my point:

where Jamal is now – I have been ...

someday Jamal will look back on all of this and think to himself: "Gosh, there's nothing really complicated about this stuff at all. You just have to learn the rules – and then follow the rules."

actually it all really is quite simple ... the problem is that there is a LOT of "simple" stuff to learn ...
 
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