tutorial one shot

In the home page tutorial "one shots", there is a branch in rung 2 which I do not see as being required. When viewing the animation no flow is depicted for any scan through output 1001. It appears to me that the latching would take place without this branch connection. That is not to say I see this correctly, would anyone help.
jrdm.

plc?

Quel est le plc que tu utilises. (omron?) Quesque tu veux savoir au juste?

You're right, the center vertical branch is not required. Without the branch, the boolean equation would be:

1001 = (1000 AND NOT 1001) OR (1001 AND NOT 1000)

With the branch, the equation is:

1001 = (1000 OR 1001) AND (NOT 1001 OR NOT 1000)

Expanding the second equation yields:

1001 = (1000 AND NOT 1001) OR (1000 AND NOT 1000)
OR (1001 AND NOT 1001) OR (1001 AND NOT 1000)

Now (1000 AND NOT 1000) = 0, and (1001 AND NOT 1001) = 0, so we're left with:

1001 = (1000 AND NOT 1001) OR (1001 AND NOT 1000), which is identical to the equation without the branch.

I looked at that and started to reply but backed off because the explaination made sense.

This is a one shot issue so left alone the one shot would be false on second scan and if the branch of rung 2 wasnt there what would latch the circuit? A one shot doesnt latch a contact unless its a Set ( or in AB a Latch) coil. I took it that on second scan that 1000 XIO would be true and 1001 XIC would be true therefore the latch would be made for 1001 coil.

Ok I cant believe that none of the pro's have NOT read the tutorial even if just to offer advice/criticism. I read it and thought I understood it but didnt attempt to use it in a plc.

Hey Joe de Montreal, keep your french inside your Quebec border, and someone out here might understand you.

OK, let's leave the branch out and do the same scan-by-scan explanation. Here are the rungs: (I left the 0500 coil out).

 0000     1000

-| |-----|DIFU|-





 1000  1001    1001

-| |---|/|--|--( )-

            |

 1001  1000 |

-| |---|/|--|

 

Start with 1001 OFF. It will remain OFF until 0000 comes ON.

In the scan in which 0000 first comes ON, 1000 will be ON. In the second rung, in the top parallel branch, 1000 is TRUE, NOT 1001 is TRUE, so the coil will be turned ON (TRUE).

In the next scan, 1000 will go OFF. In the secnd rung, in the top parallel branch, 1000 is FALSE and so is NOT 1001 (remember 1001 was turned ON during the last scan). In the bottom parallel branch, 1001 is TRUE, and NOT 1000 is also TRUE, so the coil remains in the ON state. This condition will prevail until something changes.

Now when 0000 changes back to OFF, nothing happens to 1000, so nothing changes in the second rung.

The next time 0000 goes ON, 1000 turns on again for one scan. During that scan, in the second rung, the top parallel branch, 1000 is TRUE, but NOT 1001 is FALSE (remember, 1001 is still ON). In the bottom parallel branch, 1001 is TRUE, but NOT 1000 is FALSE. Neither of the parallel branches are TRUE, so the 1001 coil is turned OFF.

During the next scan, in the top parallel branch, 1000 is FALSE and NOT 1001 is TRUE. In the bottom parallel branch, 1001 is FALSE, and NOT 1000 is TRUE. Again, both parallel branches are FALSE, so the 1001 coil remains OFF, and will continue to remain OFF until the next time 0000 goes from OFF to ON.

AM I missing something or did you just answer the question why one shots are used?

Seems to me you just answered why one shots are used and WHY the branch of rung 2 is needed...example: one pushbutton to turn on/off one output.

You stated:
Start with 1001 OFF. It will remain OFF until 0000 comes ON.

In the scan in which 0000 first comes ON, 1000 will be ON. In the second rung, in the top parallel branch, 1000 is TRUE, NOT 1001 is TRUE, so the coil will be turned ON (TRUE).

In the next scan, 1000 will go OFF. In the secnd rung, in the top parallel branch, 1000 is FALSE and so is NOT 1001 (remember 1001 was turned ON during the last scan). In the bottom parallel branch, 1001 is TRUE, and NOT 1000 is also TRUE, so the coil remains in the ON state. This condition will prevail until something changes.

What if the input is true again..ie if a pushbutton pressed again?
You stated:
The next time 0000 goes ON, 1000 turns on again for one scan. During that scan, in the second rung, the top parallel branch, 1000 is TRUE, but NOT 1001 is FALSE (remember, 1001 is still ON). In the bottom parallel branch, 1001 is TRUE, but NOT 1000 is FALSE. Neither of the parallel branches are TRUE, so the 1001 coil is turned OFF.

During the next scan, in the top parallel branch, 1000 is FALSE and NOT 1001 is TRUE. In the bottom parallel branch, 1001 is FALSE, and NOT 1000 is TRUE. Again, both parallel branches are FALSE, so the 1001 coil remains OFF, and will continue to remain OFF until the next time 0000 goes from OFF to ON.

Isnt this a standard toggle circuit?

I got the what ( or is that which) plc are you using. I am not sure about the rest, the dialect is killing me. I think you are saying "you are right or I know you are right", something along those lines.

I try but my abilities at other languages is probably on a par with plc's, I know enough to get by but not do every day.

Hi Folks,

I literally received 7 emails today asking this same thing. I thought it was strange and figured some school was using it in their class and the teacher recommended emailing the question. But now I know it was just lurkers from the forum.
Don't be shy folks... the forum is full of helpful and friendly people. So ask away!!!

I think the answer has been explained quite well before my reply. The branch is not needed. I added it basically to make the animation easier to follow. I wanted to show the impression of a 'brick wall' during one of the animation frames. In hindsight, perhaps it doesn't make things easier to follow...

So, here's the animation without the branch... and slowed down to about half speed.



Here's the original with the branch for comparison.



When writing about the one-shot I tried to find a cool use for the instruction. At the time, the 'coolest' I could think of was a flip-flop. If anyone has any other interesting 'quick apps' for the one-shot please post them. I'm always interested in 'quickies' as well.

Enjoy,

Phil,

I used this type of flip-flop on different types of PLC's and it worked every time. I use to write it down as

|  0000     1000

+--| |-----|DIFU|-

|



|  1000    1001    1001

+--| |-----|/|--+--( )-

|               |

|  1000    1001 |

+--|/|-----| |--+

|

and in this case it's clearer that this is in fact an EXOR-function between the edge detection and the output.

I always tell my trainees to use edge detection to construct a safe(r) start/stop like this:

|  0000     1000

+--| |-----|DIFU|-

|



|  1000    0001    5000

+--| |--+--| |-----( )-

|       |

|  5000 |

+--| |--+

|

With this logic you have to release the start button and press it again to start a second time, so every "clever" guy who's blocking the start button is no longer endangering lives.

Kind regards,

Jean Pierre Vandecandelaere

BTW for Joe from Montreal: if you understand English it's basic courtesy to answer in English since the person who's asked the question maybe does not understand anything else but English.

BTW for Vetteboy: this forum is also not the place to fight a language battle. If you don't understand a post, don't answer it unless you have some value to add. I always admire those who don't have a good knowledge of English, but are willing to put some effort in it. Fooling around is OK if someone is clearly asking it, but for the rest: try to keep it positive!

BTW for all involved: for me too, English is not my native language. So sorry if it is not always correct. I apologize.

Sorry Jean Pierre, Canada isn't all just peace and love you know. I was just observing the fact that the world doesn't have to conform to Quebec's reverse discrimination language laws. You can't hang an english sign up in Quebec, but you can hang a french or chinese sign anywhere else in canada. I just thought if he wanted to be understood in a mostly US site, he should try english, even if his parents hate him for it.

I know the situation Vetteboy. Although 60% of Belgium is Dutch-speaking, the French speaking part is stil dictating the laws in Belgium. For exchange we (the Dutch speaking part AKA Flanders) gets the Prime Minister, and that's no certainty either!

But since most Flemish people speak 3, 4 or even more languages, we don't consider it a problem. We know we're the best: we understand French, the French don't understand us!

Kind regards

Jean Pierre Vandecandelaere

Hi Jean Pierre,

Your re-draw is certainly much clearer. And a good 'quickie' example application as well. Thanks for sharing!

By the way, Steve, my hats off to you as well for the boolean work and later scan explanation. It's always good to see the laws at work. Well done.

Enjoy,

What I could use some help on is machine code. Our plc,s interface with internal code, can anyone offer insight.
Regards,
Dataglyph

dataglyph,

Actually, all PLC's interface with internal (machine assembly language) code. You really have to be a little more explicit. What kind of insight do you really need?

I would love to explore this, but your question is way the hell too broad.