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Old August 12th, 2003, 06:16 PM   #1
sicminds
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CarWash Ladder Logic

Hello,

I am looking for help on the ladder logic of a automatic carwash.

I need to make a basic ladder logic program for the entire wash, and also need a complete ladder logic program for one of the processes like the "spin brushes"

I have to make the program work with an allen bradley 500

PLEASE HELP
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Old August 12th, 2003, 06:19 PM   #2
Tom Jenkins
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You're out of luck - we don't do your homework for you on this site.

Start by making a "Point List" of all the inputs and outputs, their descriptions and functions, and voltage level.

Create a text description of each step of the logic.

Create a text list of all the alarms and what triggers each.

Start writing your code, one step at a time. If you have problems with a specific step, post the logic you have written here and we will be happy to help with your specific questions.
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Old August 12th, 2003, 07:13 PM   #3
sicminds
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Last edited by sicminds; August 12th, 2003 at 07:21 PM.
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Old August 12th, 2003, 07:19 PM   #4
sicminds
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The single process Ladder Logic

A Input Sensor is needed to sense the vehicles presence, once the vehicle is detected to turn on a conveyor belt motor. The motor should stay on until input sensor 2 detects that the vehicle has made it to the pre-rinse location. After the conveyor motor is turned off, a water pump should be turned on for a certain time period of 30 seconds, once that 30 seconds has past it needs to be shut off.

|------| |-----------------------( )-----------|
|------| |------------------|-----( )----------|
|---------------------------|-----( )----------|
|---------------------------|____________|
|---------------------------|-timer------|
|---------------------------|-timebase 30|
|---------------------------|____________|
|---------------------------( )----------|

Is that even close to what it is supposed to look like? Once i understand this single process i will be able to do the complete
process. So please give me some help and point me in the right direction.........

thanks!
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Old August 12th, 2003, 07:37 PM   #5
panic mode
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nope but keep trying... The only way to learn is by
doing it yourself. If you have a question about particular
function or rung - that much can be answered.
The best you can try (unless you have access to real PLC)
is to work with ladder simulators. Some should be on this site
as well (I never tried any).

Short advice when posting program:
edit your logic in notepad (set font to courier for example).
once you paste it in the new message put LADDER tag before it and /LADDER after (tags shall be surounded by square brackets
such as [ and ]).
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Old August 13th, 2003, 01:02 AM   #6
Pierre
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Here is a starter for you:
============================
Point A : There is a car and it is detected.

I:0/0
----||--------(O:1/0)


Where I:0/0 is where you have connected your "Input sensor"
...and O:1/0 is the Output that drives whatever this conveyor is runnning from.

OOOOPPPSSSS !!!!!<Once the car is no more in front of the sensor, the conveyor will stop.

So I need to latch this output.

I:0/0
----||----+----(O:1/0)
O:1/0 |
----||----+


OOOOPPPSSSS !!!!!<This conveyor will never stop

So Sensor no 2 goes in...but just where?

OOOOPPPSSSS !!!!!<

What if the motor conveyor motor does not start?
What if I get a signal from the sensor in the wrong sequence?
What if its not a car but Terry's dog walking in while the doors are open?

You will not be able to write this code IF you do not use your head.

Write the INs and OUTs IN PLAIN TEXT
Write the sequence IN PLAIN TEXT
Write all the "What ifs" you can imagine IN PLAIN TEXT

THEN :

Structure your program : Give it a little logical order

How many sub-system will this system have, use one ladder file for each.

Within each ladder file plae the real outputs at the very bottom and the steps of logic starting in order from the top.

THEN :

Write the comments you would place on the first rung.

Example :

"This rung resets all counters and timers on initial power up of the PLC"

Then and only... write the code for this rung. Its should match the comments.

Of course you do not have to follow this procedure sooo strickly that you pass-out, blod flowing from your eyes, but it shows you that the most important thing about a program is:

STRUCTURE,STRUCTURE,STRUCTURE,STRUCTURE,STRUCTURE
COMMENTS
WHAT IF?
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If it looks like a Cat...
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Old August 13th, 2003, 01:57 AM   #7
Eric Nelson
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Thumbs up Well Done, Pierre...

Quote:
Originally posted by Pierre
Write the INs and OUTs IN PLAIN TEXT
Write the sequence IN PLAIN TEXT
Write all the "What ifs" you can imagine IN PLAIN TEXT
And be sure to keep a few spare reams of paper handy for the additional "What ifs" that you DIDN'T imagine...

Which, in turn, will require more paper to write down the additional I/O that you now realize you need... utoh

Which will require even more paper to re-write the original sequences (and add more sequences) to cover all these newly discovered "What ifs" and additional I/O points... banghead

Now you can start writing the program...

beerchug

-Eric

P.S. If you plan to generate a printout of your program, you'd better go get some more paper!...
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Old August 13th, 2003, 09:23 AM   #8
Tom Jenkins
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You've made a good start, sicminds. Elaborate a little more detail in your logic description, including specific inputs and outputs. For example:

Proximity switch 1 detects vehicle
Then conveyor motor starts
Conveyor runs until proximity switch 2 detects vehicle is at at pre-rinse station
If vehicle is not detected by proximity switch 2 within 15 seconds set an alarm
Conveyor stops if proximity switch 2 detects vehicle
If vehicle is at pre-rinse station and conveyor is stopped pre-rinse pump starts
Pre-Rinse pump runs for 30 seconds and stops

You have the right idea in your logic. Remember, contacts --| |-- represent the "if" portion of the description. Outputs or internal coils represent the "then" portion. Paralell contacts are "or" and series contacts are "and". Normally closed contacts are "not"

Code:
    Prox1           Prox2       RunConveyor
-----| |------+------|/|---------(O1)
              |
  RunConveyor |
     O1       |
-----| |------+
You read this in English as: (If Prox 1 is on OR the conveyor is running) AND Prox 2 is NOT on THEN Run the conveyor.

Incidentally, the paralell contact in my post and Pierre's is called a "holding contact" or a "latching contact". It is an incredibly useful little bit of logic that is used to keep something running once it starts, until another event occurs to make it stop. You will use this logic in one form or another a lot in your program.

Keep at it - you are doing OK for a beginner.

Last edited by Tom Jenkins; August 13th, 2003 at 09:31 AM.
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Old August 13th, 2003, 02:40 PM   #9
Pierre
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Why are they using mechanical limits switches?

Where:

I:0/0 detect the incoming car.
I:0/1 detects that the vehicle has made it to the pre-rinse location.
O:1/0 starts the conveyor

Is It going to be

This?
Code:
   I:0/0         I:0/1        O:1/0        
----| |-----+------|/|---------(  )
            |
  O:1/0     |                          
----| |-----+
OR

This?
Code:
   I:0/0         I:0/1        O:1/0        
----| |-----+------| |---------(  )
            |
  O:1/0     |                          
----| |-----+
Ask yourself:

Do I want the sensor signal to be normaly High or Low when NO CAR is in the system?

If this signal was to disapear, kaput, gone. What do I want my system to do?

See? Only one input and already many what-ifs.
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If it looks like a Cat...
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Old August 13th, 2003, 03:53 PM   #10
jthornton
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Re: CarWash Ladder Logic

Quote:
Originally posted by sicminds
Hello,

I am looking for help on the ladder logic of a automatic carwash.

I need to make a basic ladder logic program for the entire wash, and also need a complete ladder logic program for one of the processes like the "spin brushes"

I have to make the program work with an allen bradley 500

PLEASE HELP
Feel Free to contact us to do your programming for you. Programming is the reason my family eats under a roof at night. Of course you will have to pay us to do that...

John
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Old August 13th, 2003, 05:31 PM   #11
Terry Woods
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Everybody knows you need to... Be the Car!
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Old August 13th, 2003, 05:44 PM   #12
jthornton
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and bring lots of Beer for Terry and the rest of us...
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Old August 14th, 2003, 07:06 AM   #13
RSVIEWRULZ
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a t hought

There is one thing of understanding the code you need to write as well as understanding the software. This includes thinking logicly.

But it is another to understand the engineering of the process. Knowing the inputs required, inputs recieved, outputs etc...

Shouldn't this guy/gal start with writting a description of operation?

Is there a button to start the car on down the track, a LS to sence a rollar has been sent? How does the length of the car get sensed?

Is the hydraulic unit started with the sending of the car or is it all seperate functions...

It always makes it easier for me to know what the operation will be and all the functions... This way I can also do the What if senarios before I even start. Also reduced the amount of time to write code...

Knowing and understandint the process helps....
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Old August 14th, 2003, 02:54 PM   #14
Eric Nelson
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Re: a t hought

Quote:
Originally posted by RSVIEWRULZ
Shouldn't this guy/gal start with writting a description of operation?
Hence the need for a large supply of paper!...

beerchug

-Eric
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Old September 1st, 2005, 12:18 AM   #15
gb_patel2003
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How do i connect computer monitor and keyboard to PLC for changing parameters?
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