A few questions

Hey all, I'v got a few queries. hopefully they can be resolved. In our notes we are given a memory latch facility example as follows:
Q.1

      X1         M0     

------| |--|-----( )-------

           |

      M0   |

------| |--|



      M0         Y0

------| |--|-----( )-------



      X0         M500

------| |--|-----( )-------

           |

      M500 |

------| |--|     



      M500        Y1

------| |--|-----( )-------



----------------------[END]--

What is confusing me is how can an input and an output have the same name? In the first line there are two. Also in the 3rd line there are two M500. How can M0 turn on M0 or is this just associated with a memory latch?

----------------------------------------------------------------------
Q.2: In our exam there is the possibility that we might be given a ladder diagram and solution but asked to phrase a question or make up an example where the problem might be used in industry.

      X0

------| |------[SET][M0]------



      M0        K5

------| |------(T0 )----------



      T0        K5

------| |------(T1 )----------

          |

          |    Y0

          |____( )------------



       T1       K5

------| |------(T2 )----------

          |

          |    Y1

          |____( )------------





      T2       K5

------| |------(T3 )----------

          |

          |    Y2

          |____( )------------





  T3            

------| |------[RST][M0]------



---------------------[END]----

When X0 is turned on M0 is SET to on. M0 then drives Timer T0. Once Timer T0 times out, Timer T1 is activated and output Y0 is turned on. Timer T1 times out allowing Timer T2 and output Y1 to be driven on. When Timer T2 has timed out, Timer T3 and output Y2 are activated and Timer T3 times out and resets M0. This resets all of the outputs and Timers, until Xo is remade.
So just a quick recap. What kind of question could be posed to come up with that answe. Its like working backwards but Im finding it difficult. Given an answer but have to make up a question.

You don`t need all that code, just be happy with the code you have. What is important is health and happiness

Format C
When you located in Rittal cabinet what left?
Just health and happiness.
And e-bay of course.

smart arse.

What is confusing me is how can an input and an output have the same name? In the first line there are two. Also in the 3rd line there are two M500. How can M0 turn on M0 or is this just associated with a memory latch?

Click to expand...

You have answered that question yourself, M0 (output or coil if you like) is turned on and is then latched on by it's own contact. The -| |- and -|/|- are not just inputs, they can be a contact associated with an output or a memory bit. In the example you posted M0 and M500 can be turned on and latched but not unlatched, lucky this is just an example and not a real world application.

Your question 2 could be something like:-

Draw a ladder diagram, that when a push button is pressed, 3 lights light one at a time, 5 seconds after each other and when all three lights are lit, turn them all off after 5 seconds until the button is pressed again.

Or something like that.

Paul

so the example makes no sense?

UL Student said:

so the example makes no sense?

Click to expand...

I wouldn't say it makes no sense, it certainly shows you the way to not program, being able to turn something on, but not able to turn it off is not a good idea.

If you had put that code into a PLC and run it, you would see what I mean, what you would have to do then is edit your code to allow you to turn the outputs back off. That might have proved to be a useful learning exercise. You also didn't need to use the M bits to turn the outputs on, your code could have looked something like this:-

   X1        Y0

--| |--+----( )

       |

  Y0   |

--| |--+

Or with a means of turning the output off:-

   X1      STOP    Y0

--| |--+----|/|---( )

       |

  Y0   |

--| |--+

If you click the 'learn PLC's' link at the top of the page you can then go through Phil's excellent tutorial.

Paul

ArikBY said:

Format C
When you located in Rittal cabinet what left?
Just health and happiness.
And e-bay of course.

Click to expand...

beerchug to health & happiness !!!

I will beerchug for that