When PLC programming

Your question as phrased is hard to understand. A switch that is wired correctly across its NO terminals is understood to be open when in its non-actuated state. Open means there is no current flow across its contacts. There are no conditions other than open and closed.

I don't know what "deadened" means in this context. Do you mean the past tense of the verb "deaden" as in "The addition of thermal insulation also deadened the ambient noise"? Do you mean "dead end" as in "This avenue of research is a dead end"? Do you mean "dead-ended" as in "The road dead-ended at the washed-out bridge"?
 
Greg
I had some trouble in the past with the concepts of "true" and "false", especially with A-B and their "XIO" instruction.
Anyway, a good example would be a start button or an H O A switch. As Steve pointed out, when those switches are de-energized, meaning no one has pushed the button or operated the switch, they would be open, contacts are open, no power passing. (N.O.) So, an input instruction in your logic, that would look like a normally open contact on the prints, would not be green (in the case of A-B)and therefore not passing power down the rung, and so it would be false. Power from the field switches has not come into the input on the card. When the switch is energized, then the instruction would go "true".

Something like a stop button, or a high temp cutout, those would be normally closed (N.C.) and when energized, they would open. So in the logic, they would show "green" if they WERE NOT energized, or true and go false when opened. I'm sure you know most of this, but it can be confusing sometimes. Hope this helped you.
 
Greg
That drawing looks suspiciously like a start circuit or a pushbutton circuit to energize the coil on the first line. The contact that is below the first one, (the backtrack one) would be an aux contact on the coil and act as a holding circuit. You'll have to look up some of this when you have time.
The contact on the second line could be another aux contact and the coil could be a light. Run light.
So in logic, those contacts would be inputs, and those coils outputs. Your logic would seal in the start circuit and keep the output energized after you lose the input from the start button. Hope this helps. I'm going to say "deadened" means not energized or false.
BTW, the second contact ought to be a normally closed as a stop button, the first one would be start. It would have to be that way for it to work as I described above. Have a great weekend!
 
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The logic flows from left to right, so the one that drops down is not backtracking. When you have bits in separate branches like that (in parallel), they are OR statements. When they are next to each other (in series), they are AND statements.

So the first rung of that logic is saying that EITHER of those first contacts AND the lone contact further down the rung must be "true" in order for the output on that rung to be energized.
 
Your question as phrased is hard to understand. A switch that is wired correctly across its NO terminals is understood to be open when in its non-actuated state. Open means there is no current flow across its contacts. There are no conditions other than open and closed.

I don't know what "deadened" means in this context. Do you mean the past tense of the verb "deaden" as in "The addition of thermal insulation also deadened the ambient noise"? Do you mean "dead end" as in "This avenue of research is a dead end"? Do you mean "dead-ended" as in "The road dead-ended at the washed-out bridge"?

Well Deadened was supposed to mean dead end and I never seen deaden before had to look that one up lol I didn't do to well in school something called ADHD takes me a while to understand stuff.
 
The one that drops down and backtracks why would that one be false and wouldn't that be a deadened

You are looking at it the wrong way. That one doesn't drop down and backtrack, it's just called a branch and is a way to put input instructions in parallel.

Each rung, has inputs on the left side, and outputs at the far right, the condition of the input instructions will keep the output off or turn it on.

On that top rung, you have three input instructions, say they are from three different pushbuttons:
PB1, the first instruction at the top of the branch
PB2, the one to the right of PB1
PB3, the one at the bottom of the branch

If PB1 is pressed, that instruction at the top of the branch will turn on. THe output will not turn on, because the PB2 instruction is still off. It will also not run on the PB3 instruction on the bottom of the branch (the backtracking, because PB3 is not pressed. That one on the bottom will only turn on when PB3 is pressed.

Now, if PB2 is pressed, that instruction that is not on the branch turns on.
Again, the output will not turn on, even through the instruction right to its left turns on, because there is not a complete path from the far left of the rung to the output.

If PB2 is pressed, and either PB1 or PB3 is pressed, now one of the instructions on the branch is on, and the instruction to the left of the output is on. The output will turn on, because there is a complete path from the left to the right.

IF PB2 is pressed, to turn on the output, it does not matter is PB1 or PB3 is pressed, it only takes one of the branch instructions being on to complete the path to the output.


So if you are just looking at that rung, either of the two branch instructions in parallel can be on, and the instruction that is not on the branch must be on, to turn on the output.

THe branch (parallel) instructions kind of act like an OR.

If the rung just had two instructions, no branches, that acts like an AND.

So for the top rung that you posted the output is on if (PB1 OR PB3) AND PB2) is true.
 
Remember that this is simulating or emulating a circuit that could be built with real relays. It's all about completing a path from the left "power rail" to the output (load) on the right.
 
You are looking at it the wrong way. That one doesn't drop down and backtrack, it's just called a branch and is a way to put input instructions in parallel.

Each rung, has inputs on the left side, and outputs at the far right, the condition of the input instructions will keep the output off or turn it on.

On that top rung, you have three input instructions, say they are from three different pushbuttons:
PB1, the first instruction at the top of the branch
PB2, the one to the right of PB1
PB3, the one at the bottom of the branch

If PB1 is pressed, that instruction at the top of the branch will turn on. THe output will not turn on, because the PB2 instruction is still off. It will also not run on the PB3 instruction on the bottom of the branch (the backtracking, because PB3 is not pressed. That one on the bottom will only turn on when PB3 is pressed.

Now, if PB2 is pressed, that instruction that is not on the branch turns on.
Again, the output will not turn on, even through the instruction right to its left turns on, because there is not a complete path from the far left of the rung to the output.

If PB2 is pressed, and either PB1 or PB3 is pressed, now one of the instructions on the branch is on, and the instruction to the left of the output is on. The output will turn on, because there is a complete path from the left to the right.

IF PB2 is pressed, to turn on the output, it does not matter is PB1 or PB3 is pressed, it only takes one of the branch instructions being on to complete the path to the output.


So if you are just looking at that rung, either of the two branch instructions in parallel can be on, and the instruction that is not on the branch must be on, to turn on the output.

THe branch (parallel) instructions kind of act like an OR.

If the rung just had two instructions, no branches, that acts like an AND.

So for the top rung that you posted the output is on if (PB1 OR PB3) AND PB2) is true.

So what does the one that comes off the bottom and goes back the other way activate/do sorry if I am having a hard time understanding that one. Oh wait just read it again why would them need to be in parallel what would that do in that line.
 
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Greg, the branches don't allow the circuit to "go back the other way". They give two possible routes to the same destination. Like if you and a buddy were having an argument about the fastest way to a restaurant. One wants to take the highway, one wants to take the back roads. You guys would both end up in the same spot but you would take two different routes to get there.

The branches are OR statements. To get from where you are to the destination, you can go through the top contact OR the bottom contact.
 
The only thing that's being "activated" are the outputs. The circle symbol on the right side of the logic. The normally open contacts you've drawn (the two vertical lines) are INPUTS from the machine that are showing you a state of a sensor, or a software bit, or something like that. They become true or false based on the state of the machine/program.
 

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