Ladder Logic Help

[skelly]

Greetings,

This is my first posting. It looks like an awesome forum with many interesting topics.

I'm currently taking a "Introduction to PLC" course in hopes of learning more about this complex field.

I'm working on an application where I need to create a circuit that will work similiar to a rail road crossing signal (pilot lights flasing one at a time). I need to accomplish this by using solid state timers in my ladder. I'm struggling with a correct schematic. Could anyone give some help?

Thanks in advance,
Scot

 

[504bloke]

How far have you got ? Can you post what you have so far ?

Which brand of plc and software have you access to ?

 

[skelly]

Thanks for the reply.

I am using Autodesk Actrix to construct my circuit diagram.

We currently have Allen Bradley PlC controlls.

As of now, we haven't purchased a software, but I do have LogixPro PLC Simulator.

I am still in the beginning stages of constructing ladder schematic and then testing them in real wiring applications.
Thanks,
Scot

 

[geniusintraining]

Welcome to the forum

At the risk of being beat up....for posting some logic that may or may not be the correct way (but it works)

take a look at this its adjustable so you would be able to make your lights flash at whatever time interval you would like, the input is latching so you would need to (maybe) change it, this may get you started, what type AB processor are you using?

Edit:
Wanted to add your output/lights would be B3;0/5 and 0/6, I just made them bits for my program so I could see it work.

 

[Steve Bailey]

Are you working on the PLC program (ladder logic) or on the wiring of the input and output devices to the I/O modules?

On the assumption that you're writing the ladder logic, a straightforward method would be to use two timers. When the first timer is done, it enables the second timer. When the second timer is done, it resets both timers. The time when neither timer is done can be the off time. The time when the first timer is done but not the second can be the on time. The presets for the two timers determine the duration of the on and off times.

For two alternating lights, you can take advantage of the fact that you have both XIO and XIC instructions in your function set.

That's just one of many possible methods. Once you've figured out how to do it as I described, see if you can come up with a few variations.

 

[skelly]

Thank you for the replies.

I am writing the ladder logic for this application.

If I'm not mistaken, our processor is a 1755 L61, but I will have to double check.

Thanks for giving me the extra boost. I'm sure there are many ways to approach this application once I get my feet on the ground.

I'll try to scan my Actrix file for viewing. This may give you a better visual of my progress.

Thank You,
Scot

 

[504bloke]

If I'm not mistaken, our processor is a 1755 L61, but I will have to double check.

Do you mean a 1756-L61 ?