I need the answer for this plc question

It is about a car park elevator

http://postimg.org/image/vqshxtw6t/

That is a hard one, to draw the state diagram of a Car Park Elevator control system, and then make a ladder diagram for an unknown brand and model of Programmable Logic Controller.

I have not seen anyone here successfuly do this one yet, or at least they didn't say if they got it done. Maybe you will be the first to post your solution?

A guess from reading between the lines is that it is for some model of Siemens PLC, and you should then use some version of Siemens programing software to write the ladder logic.

A place to start is with the given 6 States in the problem:

1st: Waiting State, the most important and the FIRST ONE, not the 6th one as listed. The Elevator PLC will spend most of its time doing this, until someone somewhere (on floor or in car) presses a button.

2nd: Moving UP or Moving Down?
_ 2a: Moving UP
_ 2b: Moving DOWN

3rd: Car Gate Closing

4th: Car Stop

5th: Car Gate Opening

Repeat: Car Gate Closing
Repeat: Moving UP or DOWN
Repeat: Car Gate Opening

Thanks>>>
I'm not wise in plc
of course it is siemens step7
I need the full answer

Alwalid,

I cannot give you the full answer because I don't have it. I can help you to develop the full answer, then you will know how to do it, and I will learn how to do it using Siemens Step 7, instead of Rockwell.

The S6 Waiting State is mis-named. It should be called "Catch Floor Requests". That is what the elevaor is Waiting for: Floor Request pushbuttons being pressed. That would be a good place to start.

Your State "S6" (should be "S1") ladder logic would be similar to this LogixPro Simulator version (simulating Rockwell RSLogix), except your version should be written in the Siemens S7 language.

Hello

hello everyone I'm new here that really good challenging topic for new Plc user .

Thanks Lancie
I know that waiting state is the most important but wwhy chang it to S1 ?
I think it will be the same
Is the program you have written in s6?

Is the program you have written in s6?

Click to expand...

The program I have written is in LogixPro for all elevator states. The part I posted is for your State S6, (my State S1 "Catch Floor Requests and Wait"). It is Subroutine 4, because in RSLogix, File 2 is the Main prgram that calls the other Subroutines, and my File 3 is Initialization where I reset all the memory variables to 0 and set the simulated elevator car to be on the ground floor. That makes File 4 the first subroutine, the first logic that has to be done before the elevator can move: Catch (read and store) the Floor and Car Request Pushbuttons.

Yes, you can call it S6, but that implies that it is the LAST thing that your program does. But it has to be the FIRST thing that your program does, otherwise it will not work very well. Think about it: the elevator cannot move or do anything until it has instuctions: a request to go somewhere. That should be the FIRST state. Logically it has to be first, regardless of what you number it.

Why number it "6" if it has to be done 1st? This type of thing just adds unneeded confusion for me. I like to see 1st things put 1st, and last things put last.

Much of successful programming is about successful organization of the steps or states. I can say this about State Diagrams: 99% of the ones I have seen do not include ALL necessary logic states, therefore the user has problems in completing the ladder logic because of the missing states.

Yes, you are right about waiting state it should be the normal and first state.
What about the state diagram?

What about the state diagram?

Click to expand...

I never made one. I wanted as few steps as possible, so skipped the state diagrams, which normally result in many unneeded rungs being added to the ladder logic. Now would be a good time for me to go back and make State Diagrams to match my ladder logic! To me, that is the best way to make State Diagrams: write the logic, then build State Diagrams that seem to mimic the logic.

Otherwise, your program will be a maze of going here and going there, trying to follow a diagram that poorly mimics what the powerful PLC instructions really can do.

Thank you for your great help
I will try to solve the state diagram although i hate it!

Yes, state diagrams are supposed to help you write the laddder logic, but in most cases are actually very little help. I am writing one for MY elevator program, which is for a passenger elevator, so it is different from yours. I have the state diagram about 1/2 finished now.

It turned out to be more of an overall state subroutine diagram rather than a more-detailed complete State Diagram. Each Subroutine would then have its own State diagram, which would shows each decision or state that must be used.

Here is a slightly better diagram.

Thanks Lancie
Is this state diagram gives the same ladder diagram?

Yes, the state diagram is for the only elevator program that I have written. Well, not exactly. I once did one in a spreadsheet for troubleshooting an old obsolete 1950's relay-controlled Otis Elevator. I have that program if you are interested.