Tutorials of PLC traffic lights

sebulani95

Member
S
Join Date
Oct 2018
Location
Uk
Posts
5
Good afternoon,

I am studying my HNC and we have PLC classes. I am a beginner, the course has started in August and we are going to have an assessment next week. There is part of a practical exam and I am looking for PLC tutorials, actually questions and preferably with answers.

I want to try to draw ladder diagrams on a sheet of paper and then put it into Mitsubishi FX14 programme. I need to practice a bit, the basic ladder diagrams I know and I am okay with that. I am looking for someone who could create/find out any questions with traffic lights/car park system etc. There should be required to use timers, counters, NO, NC, OR and AND gates and RST and basically I think that's all. If possible with answers then I could check it.

Thank you. I hope it is the right place to ask for it.

Regards.
 
The professionals on this site will help you in the following way:


You post what you are trying to accomplish and what you have written so far. Note what does not work and what you are confused by.


They will respond with questions which will lead you to discovering what you need to do. This is called learning.


Awaiting your post with you current attempts.
 
I was absent as I have some health progm. No it’s not what I mean, I just looking for someone to develop a questions for me/maybe someone have already any questions similar to this? and then I can try myself. I just do not have access to any proper questions and couldn’t find out anything similar in web.

What I mean for example is:
Develop ladder diagram for traffic lights where red last for 50s after this yellow and green for seconds, sentence repeat or sth like that. But to be written in PLC way.
 
I don't understand why you would need questions with answers unless your homework assignment is to ask a question that other students have to answer.
 
Hi, and welcome to the forum!!
If you think a little about traffic control, you'll come to the conclusion that you will need as you said timers, inputs, outputs, etc. You could also run the lights off a combination of vehicle counts and cycle time. I have been working on a traffic light program in my spare time basically just to keep sharp. I created so far a routine for the crosswalks, which is somewhat challenging. Imagine yourself or better yet go to a major intersection and observe what's going on and you'll be able to write your logic. Good luck!!!
 
Hello, thank you very much for your answers it helps me a lot. I have done some basics traffic lights programme but now I am struggling with a bit more advanced conveyer system. I need help, could anyone check my PLC programme? In yellow we can see the exercise that I have to do. In second picture is ladder diagram made by myself however I think there might be some bugs but don’t know where, it doesn’t work in Mitsubishi Fx13 plc programme. And I would like to ask about final part of there is only contact T0 active RST the whole process will start again? Or I have to put another T0 to activate Conveyer Y0?

Thank you.

I am not sure if photos on forum works so putting my photos on photo hosting, links below:
Www.zapodaj.net/4a0ac27acc478.jpg.html
https://zapodaj.net/89491feefcbc3.jpg.html
 
Last edited:
Take another look at rung 001. What is supposed to trigger the counter?

A PLC program should loop back from the end to the beginning in an endless cycle. There is nothing you have to do to make that happen. In order to get the conveyor motor to start again after the product has dropped you may want to take a step back and get a better look at the big picture. Getting the whole system to start and stop is not the same as getting each individual part of the system to start and stop.


Bubba.
 
Last edited:
Hmm I was looking on ring 001 and there is no necessity to start counter as once the Motor(conveyer starts running) it activate immediately counter ( counter is attached to Y1 N.O contact in ring 002. Is there anything wrong with that?
 
sebulani95 said:
Hmm I was looking on ring 001 and there is no necessity to start counter as once the Motor(conveyer starts running) it activate immediately counter ( counter is attached to Y1 N.O contact in ring 002. Is there anything wrong with that?
Click to expand...

Nothing, if you're only interested in the number of times the motor gets started. But since you seem to be using the counter to open a door and turn on a lamp, that probably isn't going to be very helpful. Unless you want to start and stop the motor 12 times (?) before opening the door and turning on the light?!?

Take a step back. Describe what you're trying to accomplish WITHOUT the code.

Your first rung (0) is pretty clear: You want to turn on the motor when the START button is pressed, and once running it stays running until the STOP button is pressed.

So when do you open and close the door? Turn on the light? Etc.?
 
Hmm I thought that the counter work like that: if set to count 12 he is just counting that’s it and once it reach 12 it will result that the C0 contact will be activated, am I wrong? 🤔
 
Yes, you are wrong, and that is not how a counter works. A PLC counter will increment once each time the it sees the preceding condition(s) change from false to true. So in your case, the counter will increment once when the motor is started the first time, but will not increment again until the motor has been stopped, and then started again.

When I have to write a program from scratch I usually fall back to my early training in relay logic. In your case it would go something like this. IF the system is running, AND the motor start button is pressed THEN start the motor. IF, AND, OR and other such terms are the inputs that will lead you to the THEN which is the output for the rung.
This is the simplest way I know to get simple digital logic from paper to PLC program.
 

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