PLC questions

nautica03 · Jun 29, 2005

Electronic programming gurus...

Given two single - pole switches, write a program that will turn on an output when both switch A and switch B are closed?

Given two single - pole switches, wirte a program that will turn on output when either switch A or switch B is closed?

Given four NO (Normally Open) pushbuttons (A-B-C-D), write a program that will turn a lamp on if pushbuttons A and B or C and D are closed.

I seem to be stuck. Help would be greatful.

randylud · Jun 29, 2005

AND for the first situation
OR for the second situation
AND+OR for the third situation.
IF all else fails, ask your instructor!

nautica03 · Jun 29, 2005

I'm new to this. Basically i was given a book called PLC and from reading chapter one it doesn't say anything about switches. all it provided was info on what are PLC .. so when doing the question 1. It doesn't make no sense. i'm new, it's like learning a new language with no where to start at. :|

bernie_carlton · Jun 29, 2005

Take your questions. Instead of "write a program" read it as "draw a circuit diagram". Make those drawings. That is your starting point.

randylud · Jun 29, 2005

Take Bernie's advice and then look back at my first post!

nautica03 · Jun 29, 2005

wow thanks you guys. I got it. It consist of and or gates. ^___^

student at itt-technicial institute of technology majoring in CEET .. computer electronic engineering technology. ^____^

rsdoran · Jun 29, 2005

Given two single - pole switches, write a program that will turn on an output when both switch A and switch B are closed?



      A       B      output

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

This is an AND..A and B...if A and B are TRUE then turn on ouptut.

Given two single - pole switches, wirte a program that will turn on output when either switch A or switch B is closed?



      A           ouptut

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

|     B      |

|----| |-----|

This is an OR...if A or B is TRUE then turn on output.
For the above outputs to stay on the inputs must stay on.

Given four NO (Normally Open) pushbuttons (A-B-C-D), write a program that will turn a lamp on if pushbuttons A and B or C and D are closed.

This is not defined properly, are the pushbuttons maintained or momentary?

bernie_carlton · Jun 29, 2005

Who cares what the external inputs are (maintained or momentary). The logic is the same for the question as written. Now if it had been written as "A THEN B or C THEN D" then it might be time to question.

rsdoran · Jun 29, 2005

bernie_carlton said:
Who cares what the external inputs are (maintained or momentary). The logic is the same for the question as written. Now if it had been written as "A THEN B or C THEN D" then it might be time to question.

You are probably right, all these are simplistic so its just A and B and C and D is true then turn on output.

I think I read more into because the original questions stated "switches" and this one did not. That left it open to a few things...ie WHO HAS 4 HANDS?

Using bernies asessment and the 4 pushbuttons are momentary then you have to keep them pushed down for the output to stay on. If they are maintained then you just have to push once to latch them into the maintained position.



     A     B     C     D   output

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

Terry Woods · Jun 29, 2005

Good Grief...

Switches A & B...



   A       B

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



   A

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

       |

   B   |

--| |--+





Push Buttons, A, B, C and D...



         Turn Off

          Output

   A      (N/C)

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

       |

   B   |

--| |--+

       |

   C   |

--| |--+

       |

   D   |

--| |--+

       |

Output |

--| |--+  <-- This is a Latch until Turn Off Output is pressed

Geez...

rsdoran · Jun 29, 2005

That is why I didnt think it was defined properly.
He stated A B OR C D are closed...wasnt sure how he actually meant it but had an old age moment after bernie's reply.

TECHNICALLY:



     A     B      output

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

|    A     B    |

|---| |---| |---|

If the buttons are maintained, if not then add:



   output

|---| |---------|

OR take your pick...
BUT
If momentary how do you turn the output off?

Terry Woods · Jun 29, 2005

Ooops...

Right you are Ron.

Eric Nelson · Jun 29, 2005

rsdoran said:

I realize it's a typo, but it's quite funny when pronounced... "Oop Tut"...

-Eric

sufi85 · Jul 9, 2012

boolean expression

hi all,

i am redzuan from malaysia and beginner to learn PLCs. can u help me to settle this problem?
the question is:-

write the Boolean expression and draw the gate logic diagram and typical PLC ladder logic diagram for a control system wherein a fan is to run only when all of the following conditions are met:

*input A is off
*input B is On or input C is On, or both B and C are on
*inputs D and E are both On
*One or more of inputs F,G or H are On.

hope u all can help me.

thanks,
redzuan.

bernie_carlton · Jul 9, 2012

Start small. Show all three methods of control for just the first condition:

input A is off

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