Pull cord logic

[sean90a]

Hello everyone,
I am new and this is my first time and I am in the process of learning PLC ladder logic.
2 pull cords and a stack light.
cars moving and 2 pull cords are placed to hold the vehicles at a point and a stack light is there to show signs.
Stack Light always red indicating do not cross.
When PC1 or PC2 is pulled, show amber when vehicle is held and the another vehicle is moving.
PC1 or PC2 can be pulled again if you want to reset because you don't want the vehicle to stop.

My logic:


-||PC1---|/|L2-----[SET L1]--
-||PC2-------------[RST L1]--
-||PC2---|/|L1-----[SET L2]--
-||PC1-------------[RST L2]
---|/|L1---|/|----(Red)--

---||L1--------||Carry out--(Yellow)--
|
|
---||L2--------|/|Carry out-----(Green)---

Carry is a point when the vehicle passes through and hits a limit

I am having trouble when PC1 is pulled it sets L1 as well RST's L2. how do alter the logic so that can be fixed.

 

[James Mcquade]

first off,
welcome to the forum.

if this is an automotive application, i must state the following:
most auto plants i have been in have a specific way of getting the job done, and you must follow that format.

you must discuss with the engineers, then safety, then union,
then get crafts to modify the program. if this is your first program i would definitely get others involved with more experience. you don't want a lot of downtime while you try to program / fix the problem. your entire plant will shut down when things gets out of time.
Is this a plc or a safety plc?
And if you are a supplier to the auto industry, you pay a huge fine for being late and can risk your contract.

Don't want to scare you, but that's what i faced on one of the jobs i did long ago.

things to consider.

regards,
james

 

[Lancie1]

Sean,

To help you solve this problem, some questions need answered.

1. A block diagram of the situation would help tremendously.

2. Explain how PC1 and PC2 work. Does each switch perform the same function (stop cars while one car moves), or are they for two directions of travel (say an intersection), or what?

3. When a car triggers the "Carry Out" limit, does the limit stay on until the car is completely clear (another car can be started), or should there be a time delay to allow moving vehicle time to clear the intersection?

 

[Lancie1]

Left to my own imagination, I imagined this setup, and solution. I am sorry if it is not the real problem.