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How does the positive transition sensing contact work

  1. Sep 14, 2014 #1
    1. The problem statement, all variables and given/known data
    Draw the time diagram for this PLC ladder

    eae91958d05b133ec3b888b5464bf3d1.png
    2. Relevant equations



    3. The attempt at a solution
    I am trying to understand how does the positive transition sensing contact work.

    Definition : The positive transition sensing contact has the value 1 if it receives value change from off to on in one scan.

    According to the time diagram I can see that :
    Scan 2 : PB1 raises from 0-> 1 (off to on) so PB1 = 1 for this scan only
    Scan 3 : PB1 remains 1, no changes so PB1 = 0 for this scan only
    Scan 4 : PB1 drops 1 to 0 so PB1 = 0 for this scan only
    Scan 7 : PB1 raises from 0-> 1 so PB1 = 1 for this scan only
    Scan 8 : PB1 no change (still on), PB1 = 0 for this scan only
    Scan 9 : PB1 (on-> off), PB1 = 0 for this scan only
    Scan 12 : PB1 (off-> on) PB1 =1 for this scan only
    Scan 13 : PB1 remains on so PB1 =0 for this scan only
    Scan 14 : PB1 (on-> off) so PB1 =0 for this scan only

    Am I understand it correct ? I know how to draw the diagram, just confused in determining the correct values PB1.
     
  2. jcsd
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