hnc student needs help!!!!

hi i am hnc student in electrical engineering, i was off with 6 broken ribs due to accident, anyway i have to design a ladder diagram, with three conveyor belts that start 20 seconds after the first. i also have to include 3 safety features. i have never done plc nor do i know were to start. please help i promise to buy you lots of beer n pub grub :nodi:

What inputs will you use? Pushbuttons, switches, auxillary-contacts, sensors; are they NO of NC.

What outputs will you use: 3 converyorbelt = 3 3Ph-motors = 3 contactors

Define 'safety feature' better:

emergency-pushbutton > normally a saftey-relay must switch off the power of the converyorbelt > a normal plc must also know the fact that the emergency pushbutton is pressed in combination with the according action inside the program

motor-breaker with aux-contact?

....


Ladder:
Ask yourself: when does a motor needs to start and when to stop?
What is the status of the inputs at the moment of 'start'?

standard start-stop-logic for the first motor
Use timers for the 2 motor who start delayed

...with three conveyor belts that start 20 seconds after the first.

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Do you mean that the first conveyor starts, then the second conveyor is delayed 20 seconds before starting, and the third conveyor is delayed 20 seconds after the second? If so, use 1 ON DELAY timer, and comparison instructions in the starting routine for each conveyor.

Which brand and model of PLC are you using to write the program? They are not all the same.

it should be last conveyor first, now the second conveyor will overflow.

FIRST you must understand what the machine does and what happens when there are screwups.

Draw a sketch of what this thing may look like.


DEFINITIONS last conveyer is 3 middle is 2 and first is 1

EXAMPLES What happens when a conveyer belt or drive component fails? Would it matter if 1 or 2 or 3 and if so why? How would you sense / detect this?

Do you need a trip wire to prevent people from being conveyed if they fall in YES it happens.

After they run do you need to shut them down in a sequence - if so why?

Is it possible you may need to run each one at different speed -- why?

How do you sense overload and what does that mean for the other conveyers?

That should do for starters.

No I am not doing your homework for you -

Now that you have answered the above
Make a list of the functions ie start which conveyer first etc etc etc.

Once you have a good written sequence of functions / tasks -- call em what you will -- you can start doing ladder.

Dan Bentler

hi, thankyou so much to the people that have replied i have completed a ladder diagram to the best of my ability, the programme does not work, i am not asking for anyone to do my homework for me i am keen to learn. if i upload the ladder diagram, can someone please point out any mistakes and guide me, that is all i ask. i have completed 11 units out of 12, i have written the report for this diagram, the report must be submitted tomorrow. 12.00 deadline please can some one educate and guide me. thankyou please reply.

the software i am using is mitsubishi fx. i do not have access to this software at home, only in college. i have attempted to down load software though i am not able to install the package, i must confess to being rubbish with computers maths yeah i seem to have masterd that, power tools love those but computers aaaggghhhh no!!!!!!!

hi, thankyou so much to the people that have replied i have completed a ladder diagram to the best of my ability, the programme does not work, i am not asking for anyone to do my homework for me i am keen to learn. if i upload the ladder diagram, can someone please point out any mistakes and guide me, that is all i ask. i have completed 11 units out of 12, i have written the report for this diagram, the report must be submitted tomorrow. 12.00 deadline please can some one educate and guide me. thankyou please reply.

You will have to ZIP your program, then attach it to your next post. Otherwise we can't help you because we don't know what is in your program. For that matter, you never really stated HOW the conveyors (3, or more than 3) are supposed to run, and how they are interlocked with each other (or not).

First, KNOW the problem. That is the only way you will ever arrive at the correct solution. Right now, I don't think you understand WHAT is the problem. I sure do not.

The software I am using is mitsubishi fx. i do not have access to this software at home, only in college.

Click to expand...

I have a free copy of Mitsubishi GX Developer- FX Version 8. Is that what you are using?

Oh, I see it was due yesterday. Too bad you didn't come here in time.