PLC help ASAP please

Discussion in 'Homework Help' started by mystang50, Aug 7, 2012.

  1. mystang50

    Thread Starter New Member

    Jun 26, 2012
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    ok need some help on a bouns plc question...quick lol

    desgin a system that will controll two traffic lights, one for control of north/south traffic and onre for east/west traffic. each direction has a red, green and yellow light. the system shall operate in the following manner:
    N/S red E/W green 45 sec
    N/S red E/W yellow 5 sec
    N/S red E/W red 1 sec
    N/S greem E/W red 45 sec
    N/S yellow E/W red 5 sec
    N/S red E/W red 1 sec
    Repeate: N/S red E/W green 45 sec
    program is allen bradly SLC RSlogic 500....
     
  2. strantor

    AAC Fanatic!

    Oct 3, 2010
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    What's my bouns? I have paypal ;)
     
  3. mystang50

    Thread Starter New Member

    Jun 26, 2012
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    shoot, if its right..............;))
     
  4. strantor

    AAC Fanatic!

    Oct 3, 2010
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    I was being facetious. I gave you the answer to your last homework question because I didn't realize it was a homework question. I failed to observe what forum I was in, and it sounded like you were an industry guy who needed help with an actual conveyor system.

    The way things work around here, is for homework help, you're supposed to show what you've done, and what parts you are having trouble with. Handing out complete answers on a silver platter is frowned upon. If you show what steps you've taken, I would be happy to guide you in the right direction.
     
  5. mystang50

    Thread Starter New Member

    Jun 26, 2012
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    oh ok i understand , i was just looking for some help with this because i am struggling in it :confused:
     
  6. strantor

    AAC Fanatic!

    Oct 3, 2010
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    Well, like I said, I would be glad to help. Are you able to post screenshots of what you've done so far?
     
  7. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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  8. JDT

    Well-Known Member

    Feb 12, 2009
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    The proper way to do this is to use a State Machine. It is the way most industrial control is done. It can easily be done in PLC ladder logic. In fact many PLC manufacturers have "state relays" as part of their programming to make this fairly simple. Probably best to Google or look at the instructions for your PLC program.

    Basically, in your case, each state will switch the lights to a certain pattern and then start a timer. When the timer finishes it moves to the next state where the same thing happens again. Your state machine will simply rotate around in an endless loop. More sophisticated state machines jump to different states depending on digital inputs.

    Start you design by drawing a collection of boxes. One to represent each state. In each box draw the pattern of lights and a time value. Then draw arrows between each box to show how they move round. Each box can then be programmed as a section of ladder logic (set/reset outputs) and a timer. Master "state" contacts control which section is currently operating.
     
  9. Bogdann

    New Member

    Jul 31, 2012
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    What do you need exactly? ladder?
    I have made traffic lite, Red,Green,Blue (HMI only). You will simply need to add ladder code that will reset 1st one when 2nd is green, or add +1 timer that will control this net, if i can call it so :p.

    I have this for Unitronics but if you need pure example of 1 traffic light so you can get to know what should be the formation of the timers i can send you this.


    edit: just saw the topic above, this should be the way to go :p
     
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