Ladder Diagram Problem

Discussion in 'Homework Help' started by McGuire406, Feb 8, 2015.

  1. McGuire406

    Thread Starter New Member

    Apr 28, 2014
    10
    2
    Hello, everyone!

    It has been awhile since I was last in this forum. At my school, we began to focus on industrial electronics and PLCs. In this, we need to become familiar with ladder diagrams and such. For one of the Lab assignments that my teacher gave us, I am having some trouble getting the ladder diagram made for the PLC program (RSLogix 5000). I was wondering if anyone was familiar with this and would help me out.

    Attached are some pictures of my work as well as the requirements for the diagram/program. Lately, I've been feeling very stressed and anxious, and it causing me not to think straight. Rungs 0 through 2 are correct, and I feel Rung 3 is correct as well. I mean, we have door a simple garage door before on a Motion Control System, so I have the base of this project figured out.

    Rungs 4 and 5 are for the "Don't kill Timmy" circuit as described in the requirements. That portion of it completely confuses me, and I don't understand how I even get the ladder logic set up for it.

    Rungs 6 and 7 are for the Maintenance Timer. Since I couldn't stay in the lab later than normal (due to work that day), I wasn't able to test these out. In my opinion, it looks like it's right, but I'm not too sure.

    To everyone that responds, thank you so much for helping me out. If this isn't the correct subforum, I'll be more than happy with moving the thread.
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,565
    2,379
    As described the 'Don't kill Timmy' is a an emergency return of the door if any blockage occurs.
    I will try and go over it today, but I have to leave for a while in an hour or so, Unless someone has pointed out anything I will get back to it later, I assume you have the SLC500 programming instruction book with you?
    Max.
     
  3. McGuire406

    Thread Starter New Member

    Apr 28, 2014
    10
    2
    This']http://www.amazon.com/Introduction-ControlLogix-Programmable-Automation-Controller/dp/1111539294/ref=sr_1_1?ie=UTF8&qid=1423417789&sr=8-1&keywords=gary dunning controllogix] This is the text[/url] that I'm using, but it pretty much explains the stuff.

    And yeah, I get what the Timmy is supposed to, in theory. It just isn't clicking with me when it actually comes to putting it on paper.
     
  4. strantor

    AAC Fanatic!

    Oct 3, 2010
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    I disagree. You haven't stated whether your physical limit switches are NC or NO, but I assume they are NO;

    If that's the case, then the way you have drawn it, the door must be sitting on either the top or bottom limit switch in order to begin moving. What if I start the door opening and then change my mind and want to close it? I press stop, it stops, i press down, it does nothing, because it isn't on the top limit. Now we are stuck in logic limbo. You would have to manually drag the door back down with a winch or something.

    If they are NC and I try to start in the middle of travel, both CR1 and CR2 will be energized simultaneously; a potentially even more undesirable result will follow.

    Also, why do you have a "start" button there?

    rungs 1-3 are entirely redundant and should be eliminated.

    Here's a hint: What do you want to happen when the sensor is triggered? exaxtly the same thing as would happen if someone pressed STOP and then immediately UP.

    No that timer instruction resets every time the input condition is removed. So the door would need to be several miles tall and run continuously in one direction for a full 40 hours before the maintenance bit would go high. This should be a counter instead of a timer.
    No, you got the right forum.
     
  5. McGuire406

    Thread Starter New Member

    Apr 28, 2014
    10
    2
    The contacts are NO, so it would be the first case. And the reason there is a Start button is because the requirements states that there should be a start/stop station.


    Ok, that makes sense.

    Oh, ok. I see what I did wrong with it. I would want to change it to a retentive timer or, as you said, a counter.
     
    strantor likes this.
  6. strantor

    AAC Fanatic!

    Oct 3, 2010
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    I think the up/down buttons should each be considered a "start" button. I would be very surprised to hear the instructor say it needs 4 buttons. The "start" button in addition just adds confusion to the operator and you. I don't even know what to do with it, or what it's supposed to do. What's supposed to happen if I press start while it's up? while it's down? While it's been sitting stopped in the middle since yesterday on a different shift and nobody knows whether it was going down or up?
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I have never used that model of SLC but this is a basis to work from obviously may have to be tweeked a little but gives an idea of what is needed.
    you will need a flashing ind light for the DKT taken off of the flash timer T3
    Max.
     
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