load cement truck program has now been edited

I HAVE HAD TO ADD BETTER LADDER DIAGRAM AS THE ONE ALREADY ON THIS POST IS JUST TOO HARD TO LOOK AT, SO I HAVE REDRAWN IT. IT IS THE ATTACHMENT KNOWN AS "CEMENT TRUCK PROJECT"


I have to design a program to load a cement truck via a conveyor belt and load a chute when truck is in position and signal the truck to stop and go by indicator lamps.

i have attached the information given (pages 1 & 2).

the working diagram is no 7 hopefully, but it didn't come out very clearly.

do you think this will work ?

i am a electrician and tafe student, studying plc's without practical experience or no exposure other than in tafe college laboratory where we write to plc via pc into a mitsubishi fx2n plc.

please help

1. Write out the process (If PB Start is pressed then turn on motor. If the Stop PB is pressed turn off motor) The example shown will help you to define the process of what you actually want to happen. This will also assist and figuring out the what if this happens part.

2. You need to make descriptions in your logic. This lets you know whats going on, and the people who try to help you.

3. Print the actual program to a PDF. Primo PDF is free, just google it. Then go to your program and print it to the PDF printer.

Hope this gets you on track!

did you look at the bottom attachment ?

Since original posting, i have entered and scanned a hand drawn diagram, called CEMENT TRUCK PROGRAM. Have you looked at this ?

I have done what you said to a lesser degree, but not sure what you mean when you say descrptions in your logic.

ROD MORONEY said:

Since original posting, i have entered and scanned a hand drawn diagram, called CEMENT TRUCK PROGRAM. Have you looked at this ?

I have done what you said to a lesser degree, but not sure what you mean when you say descrptions in your logic.

Click to expand...

Write a descriptive name above the contact i.e. X2-4 would be labeled STOP, X5 Start, etc. This allows anyone to follow the logic without having to refer to other documentation.

First off, do not overcomplicate it, think and write out what has to happen in your application. If this is a learning exercise start with the simplest scenario, making it harder is easy.

People in this forum seem to take umbrage with those who want their homework done for them, so beware. On the other hand, they seem to enjoy actually helping other's learn, which is of course different.

What you are doing here is called boolean algebra. Whether you are using actual gates on chips, a plc or another programing lanquage, it all boils down to the same thing. So, the same tools will work for all.

I do not think your logic will work. For example, it looks to me like your conveyor is going to run even if the chute is open, truck or no truck. That might put a lot of grain on the ground. Not to mention, that even if you had the chute working, which I don't think you do, you would fill the chute with the same amount of grain as the last truck to load before the next truck even parked. Don't start your conveyor until you know how much grain you need to fill the silo with, unless you want to automaticly fill it to ten tons in it's default state, since in all cases you will need at least that much for a truck. Then just add more grain if a twenty ton truck needs it. But I am getting ahead of myself.

First get a piece of graph paper or open excel. Make a truth table, each row will represent an output, the colums will represent the inputs. Then consider what your are trying to accomplish. Then mark each field as a 1 if the input condition should be true to energize the output, zero if it should be false, and put an x for "don't cares". This will force you to actually consider all the potential conditions. As another poster pointed out, writing down the rung in english will help alot.

If you want to blow your instructor away learn to use karnaugh maps and the quine mccluskey algorithm. I haven't used them in a decade, the last time I built logic with actual chips, but they are awsome if you want peak efficiency in your logic. Karnaugh maps will eliminate logic races as well, though you will usually have to combine inputs in order to limit the variables to four.

I just realized I said "grain" instead of "cement", ha, I saw silo and thought grain automaticly.

I wanted to add one more thing. You said you were an electrician, I assume that this means the type who wire houses and buildings. If you are taking a plc class, you are getting into automation and/or machines. If this is the case, you cannot spend too much time learning about ladder logic. almost every industrial machine or production line uses ladder logic in one form or another, it is everywhere. Whether as actual relays or as a plc of some sort. In fact, consider that almost every motor or valve has the potential to kill or main a person, not to mention that you can really screw up a machine, if it runs or actuates at the wrong time. In short, if you are going to actually write logic in an industrial setting, learn this stuff well don't just knock it out for the credit.

ROD MORONEY,

Here is an example of what Rsdoran is talking about

Note that the descriptons are at each address and that you don't have to refer to the descrition list. There is also an example of rung comments so others know what you are trying to do. The rung comments are invaluable for figuring out what the original programmer was thinking. Even if you were the original programmer the help especially when you havent visited this code in a while.

ROD MORONEY,

I purposely put some errors in the example so you couldn't just copy it for your homework. See if you can spot them.

thank you for your input, i think that the errors are the rung for the 20 ton selector. should be n/c x7 instead of x10. and n/c x6 instead of x7 on 10 ton selector rung. also, the output coils on these rungs should be Mo and M1 not C0 and C1 ?

ROD MORONEY,

If I'm understanding your response correctly you are right about the selection of addresses. But you are wrong about the state (you indicated NC). I don't have any mitsubishi experence or software so I used the closest match I could find (automation direct). This is why the internal relays are "C" instead of "M"

I believe you started this topic on another thread. If you want to respond please do so, but use this thread. As you might be aware of now We don't like to do students homework. But we will try to help you help yourself or give you hints. Below are some examples of threads where students were helped by this forum.
http://www.plctalk.net/qanda/showthread.php?t=18352&page=1&highlight=traffic
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