Ladder diagram problem...

[FONT=&quot]If anyone knows how to do this pls help, I have some idea, and done ladder diagram for this, but not sure if its correct. Thanks in advance.

-There is 3-floors building. On each floor there is push-button to turn on stair-lights, and push-button to turn off stair-lights. Lights will be turned on/off on all floors at same time, independently of floor where button is pressed. Light should lit only if there is no day light outside of building. Design small stair-light controller which will do this job. [/FONT]

Make a list of your inputs and outputs. Determine how they are wired. Take that information to the PLC simulator on this site and try to make something work. If at first you don't succeed, make any necessary modifications. Consider starting with a single On/Off pushbutton pair on one floor and get that to control the lights. Then expand to the On/Off pushbuttons on the additional floors. If tweaking your first attempt only seems to make things worse, try a different approach. Remember the the first law of holes; when you're in one, stop digging.

show us what you made and we will push your lightbutton.

You have the following:

1ST_FLOOR_ON_PB
2ND_FLOOR_ON_PB
3RD_FLOOR_ON_PB
1ST_FLOOR_OFF_PB
2ND_FLOOR_OFF_PB
3RD_FLOOR_OFF_PB
DAYLIGHT_SENSOR

So you want the light to turn on if
(1ST_FLOOR_ON_PB OR 2ND_FLOOR_ON_PB OR 3RD_FLOOR_ON_PB) AND NOT DAYLIGHT SENSOR.
And you want the light to turn off if
1ST_FLOOR_OFF_PB OR 2ND_FLOOR_OFF_PB OR 3RD_FLOOR_OFF_PB OR DAYLIGHT_SENSOR

You should be able to build a ladder from that.

Is this ok?

1. It looks like you need to latch an "on" signal to the lights - at the moment your lamps will light only when a button is pushed and held down. You can use either a latch instruction instead of the coil instruction, or add an extra rung to latch a memory bit until any off pushbutton turns it off (search this website for latches with reset).
2. Label your memory bits, otherwise we cannot know what your program is trying to do - without comments or bit names, working out what is wrong is much harder than it needs to be!

That's a good first try.

If you use latching output instructions you can do something like this

  ON_PB1         Daytime        Light

---] [----+-------]\[------------(L)---

          |        **

  ON_PB2  |

---] [----+

          |

   ON_PB3 |

---] [----+



  OFF_PB1                         Light

---] [----+-----------------------(U)---

          |

  OFF_PB2 |

---] [----+

          |

  OFF_PB3 |

---] [----+

          |

  DAYTIME |

---] [----+ 

**not really needed since the second rung will shut the light off in daytime but it makes the AND NOT DAYTIME condition obvious.




If you wanted to use a seal in circuit you could do something like this instead:

  ON_PB1    OFF_PB1 OFF_PB2  OFF_PB3 DAYLIGHT LIGHT

 ---] [----+---]\[-----]\[------]\[-----]\[-----( )---

           |

   ON_PB2  |

 ---] [----+

           |

   ON_PB3 |

 ---] [----+

          |

  LIGHT   |

---] [----+ 

If you have the lab time available try both. Whats important is to understand the difference between a latching instruction and a non-latching instruction.

Also, note that I have assumed that all push buttons have normally open contacts. If this isn't the case then invert the logic accordingly, and note that when inverting OR functions become AND functions.