PLC Ladder Diagram

Re: PLC Ladder diagram for 4 floor elevator

The answer lies here.

There is an existing thread running on this topic.

This sort of problem is best solved using a clocked finite state machine (FSM). Most problems are. You define each possible state of the system and then define how and when the system moves between each state. This requires a bit of initial thought and understanding, but that's not necessarily a bad thing for a machine designer

Many PLC's have FSM's built in, but if not, then you can usually set one up (on any PLC) using a register with comparison and move instructions.

eg. At start up NUM = 10, IF NUM=10 and Level is LOW then NUM = 20, pump ON. IF NUM = 20 and Level is EMPTY then NUM = 10 pump OFF etc.

One advantage of state machines is that they are easy to fault find, only 1 rung is active at any time eg when NUM = 50, only the statement IF NUM=50 .. is going to be holding things up. (compare this to the boolean spaghetti in most programs).

The speed of modern PLC's means that most programs can be written as sequential operations and it still look like they're operating as parallel.

FSM - Not to be confused with his noodly goodness the "Flying Spaghetti Monster".

Smells like homework to me....... go to www.thelearningpit.com

or www.plcs.net

cheers

And http://program-plc.blogspot.com

As mentioned check out this site. http://thelearningpit.com/. They actually have a simulation using an elevator. Writing a PLC program is fairly easy but it also depends on whci PLC you are using. You might also be able to find a programmer through the web site. Good luck

link about elevator http://program-plc.blogspot.com/2010/03/elevator-plc-program.html