Whick Timer Relay Mode/Contacts?

Discussion in 'Homework Help' started by JoeZach, May 4, 2014.

  1. JoeZach

    Thread Starter New Member

    May 4, 2014
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    Just about done with this ladder diagram except for one part.. the key element.

    Green lamp is on when motor is not running.

    Have a selector switch to go from jog to auto.

    In jog mode motor will jog forward when pushbutton 1 is pressed.

    In auto after start pushbutton 2 is pressed motor will start & continue to run.

    When the level in a tank activates a float switch the motor will stop for 15 seconds and then go in reverse until the level drops then the system will shut off.

    I have the diagram nearly completed but cannot figure out which contacts to use on the timer relay. Also which mode. In off delay contacts change positions as soon as the coil is energized. I thought the timer also started running and after the 15 seconds my NC contacts would return to the normal state and this diagram would work. But then I realized the timer doesn't run until the coil is de-energized.

    Help!
     
  2. MaxHeadRoom

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    Jul 18, 2013
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    Last edited: May 4, 2014
  3. JoeZach

    Thread Starter New Member

    May 4, 2014
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    Our Amatrol work station uses a Crouzet relay. How does this theory sound?

    The timer relay on rung 5 is energized as soon as the selector switch is closed. The normally closed float switch is in between those on rung 6. When the relay is energized the normally open contacts on rung 7 close therefore when the start pushbutton is activated the motor starts and continues to run through a seal in circuit.

    The second set of contacts on rung 8 are normally closed so they open upon energizing the TR coil leaving the reverse motor starter coil un-energized. When the float switch on rung 6 is activated it opens. This de-energizes the timer relay coil which starts the delay timer. That also de-energizes the seal in circuit on rung 7 so the motor stops.

    After the delay (15 seconds) the contacts return to their normal states. The NO contacts (to the PB) are then open so the forward motor starter is not energized. It would not be energized anyway because the pushbutton is open and the seal in circuit has been broken. Also after the time delay the NC contacts on rung 8 return to their normal state. That causes the reverse motor starter coil to be energized so the motor begins to run in reverse. That also energizes Control Relay 2 on rung 9 so the green light goes out.

    Here is a revised diagram which I reduced in size for easier viewing. Let me know if I'm on the right track please. Thanks.
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Rung 1 and rung7 both have a CR1 relay coil? I assume the second one is CR3?
    Other wise it appears to be OK.
    As an aside note on the OL's, it used to be the method for doing this in relay logic, but it is frowned on now as there is a potential for the OL to be bypassed if ever the N side of the coil goes through these OL's and happens to come in contact with ground.
    It is reccommended to be placed on the live side of the coil.
    Max.
     
  5. JoeZach

    Thread Starter New Member

    May 4, 2014
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    CR1 is the same on rungs 1 and 7. Rung one is for motor jogging when the selector switch is in the left position and is out of circuit when the selector switch is in the right position. When selector switch is in the right position CR1 is energized by pushbutton 2 but the motor will continue to run forward because of the seal in circuit and the green light is off because CR2 is also energized. CR2 appears on two rungs as well and it's only purpose is to shut off the green light any time the motor is running.

    I appreciate you taking the time to help. Where in Canada are you from?
     
  6. MaxHeadRoom

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    How can you have two CR1 coils if standard relays?

    The sunshine province, Manitoba.
    Max.
     
  7. JoeZach

    Thread Starter New Member

    May 4, 2014
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    It's the same relay. It is used to energize the forward motor contactor in either circuit. In the jog circuit it is energized momentarily. In the automatic circuit it runs continuously. it also de-energizes the green lamp in both cases as the test instructions specify.

    Finally... a friend in MB! ha ha. I'm in Pennsylvania. Spent 13 years in Montana. Have friends from the east coast of New Brunswick to central, southern & western Ontario to north of Calgary & over in Smithers and Ft Nelson BC and but until now none in MB. To me it's like the border doesn't exist.

    Does the circuit make sense?

    Go Pens!
     
    Last edited: May 4, 2014
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Unless it is a dual winding relay, you cannot have two coils of the same designation in hard wired ladder logic.
    Any rungs that apply to the same relay should be combined to output to one coil of that particular relay designation.
    If that makes sense.
    Technically you can do it in PLC ladder, but very bad practice.
    Max.
     
  9. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    What's a seal in circuit? Just curious... Really.

    [​IMG]
     
  10. inwo

    Well-Known Member

    Nov 7, 2013
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    I was going to ask. I've seen it done. Very confusing when trouble shooting.

    Never did it myself.

    djsfantasi,

    Seal or sealing contact refers to a relays own N.O. contact used to keep coil energized.

    I generally call it a latching or holding contact. May not be correct.
     
  11. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    Inwo - thanks. I've heard it referred to as latching contact myself. Perhaps it is a local phrase?
     
  12. MaxHeadRoom

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    I usually use latch contact also.
    On older prints you may see it referred to with a K notation for Keep Relay.
    Max.
     
    Last edited: May 4, 2014
  13. JoeZach

    Thread Starter New Member

    May 4, 2014
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    "Seal or sealing contact refers to a relays own N.O. contact used to keep coil energized.

    I generally call it a latching or holding contact. May not be correct."

    Exactly. Latching is another term for the same thing. Not to be confused with a seal in circus! lol

    Would representing the same output device in more than one place on the ladder diagram be called "detached symbology"?

    If not how about this revised diagram? Not so pretty but out of space. If it is more appropriate I'll redraw it properly.
     
    Last edited: May 4, 2014
  14. MaxHeadRoom

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    Jul 18, 2013
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    I would call it very confusing? :p
    Max.
     
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