Announcement

Collapse
No announcement yet.

Ladder Logic Help

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts


  • Ladder Logic Help

    Hello, I have been given a ladder logic question and because I learned ladder logic by setting and resetting control bits for every sequence it was never necessary for me to understand the control scan operations. Can anyone help with this problem? Thanks!



  • #2
    rastapapa,

    It's good to see that the schools are doing something other than tormenting students with the "flip flop". Many facets of PLC logic are scan dependent.

    Show Us what you have and I'm sure someone here will help guide you.

    PS. It's interesting that you chose this forum. If this post were two years earlier the only software and PLC CPUs that Automation Direct sold would not allow the ladder logic you posted. Direct Soft did not allow a "and above a join".
    PERCUSSIVE MAINTENANCE: The fine art of whacking the devil out of an electronic device to get it to work again.

    Vaughn

    Comment



    • #3
      I am lucky to have people who will help,

      because the PLC scans the inputs left to right, top to bottom, proccesses the logic, then updates the outputs, all in one scan.

      So what I think is in scan 1 all the outputs would initially turn on, but on the second scan because B was on, the logic would be updated turning C off.
      Scan 3 turns b& C off, but D remains on
      scan 4 has no change
      scan 5 turns B & C back on, D still is on Unchanged
      scan 6 turns off C (from xic B rung 1), and turns off D because of xic C in rung 2
      scan 7 turns everything off. like so?:


      A B C D
      scan0 0 0 0 0
      scan1 1 1 1 1
      scan2 1 1 0 1
      scan3 0 0 0 1
      scan4 0 0 0 1
      scan5 1 1 1 1
      scan6 1 1 0 0
      scan7 0 0 0 0
      Last edited by rastapapa; 01-08-2011, 09:21 PM.

      Comment



      • #4
        rastapapa,

        I see you have also found PLCs.net. You are also welcome here! I believe you have an error in 5 and 6
        Last edited by milldrone; 01-08-2011, 10:29 PM.
        PERCUSSIVE MAINTENANCE: The fine art of whacking the devil out of an electronic device to get it to work again.

        Vaughn

        Comment



        • #5
          Scan #5 has error. The rest is OK

          Comment

          Working...
          X