Flow diagram -> ladder diagram HELP

alehander

Member
Join Date
Jul 2003
Posts
16
Hello. I am attemping to convert the following flow/process diagram into a ladder diagram for use with a PLC. The entire process is fairly simple - only 9 distinct steps. I am also posting the process as an ordered list. Each step is accompanied by the associated physical device as well as an I/O designation (does the step involve input or output). While I can probably derive a crude ladder diagram, I would appreciate some help getting it up to industry standards in terms of safety and efficiency. Thanks in advance,

-Alex Bugrov
R.R. Lochhead Manufacturing

Flow Diagram:

Flow%20Diagram.GIF


Ordered List:

http://www.c-5.org/Temp/List 1.GIF

Device List:

PB1 = Push Button 1
V1 = valve 1
C1 = switch 1
V2 = valve 2
T1 = timer contact 1
T2 = timer contact 2
C2 = switch 2

flow diagram.gif
 
First, whose PLC are you using? How much have you converted so far?

Second, if you don't have a PLC vendor chosen, why do you want "ladder logic"? This is an ideal situation for a sequential function program (some vendors call this method: Step, SFC, Grafcet etc.)
 
Flow/Ladder conversion

Hello. I've got an Automation Direction DL05. The (cheap) software is not SFC-enabled, as far as I can tell. I have approximately 1/2 of the ladder diagram completed and would prefer to finish it in ladder logic. Thanks for the reply,

-Alex
 
I took a quick shot at it

It seemed like a fairly simple process so I spent about 30 minutes and came up with this...not knowing the exact system this may not work. It may not work at all, I will wait to see what the others say. I did one strange thing at the end of the program, I added a timer to reset the last counter because I didnt trust that counter resetting itself. I have done this for practice, in most situations like this the guys prefer that you post what you have done.

bottle.jpg
 
Last edited:
Ron, I noticed you used comparison instructions as 'Counter Done' bits. That's fine, but in case you didn't know, you could just use the CTn bit instead.

IOW:

| CT0
|-----] [----


is the same as:

| CTA0 Kn
|-----]=[----


if 'n' is the counter's preset value.

By the way, your ladder seems correct!... (y)

beerchug

-Eric
 
Like I said, I did it kinda fast...I did know that and dont know why I didnt use it. I did with the timer. Was hoping you would comment on it tho
 
Thanks

Hey, thanks a lot... My diagram looks fairly similar so far, except for the "counter done" bit.


-Alex
 
My version

Hello again... here is a simplified version of the above process. I am posting both the new flow diagram and the ladder logic I have developed. I would apprecuiate any advice regarding the integrity of my ladder diagram (that is, will the steps execute in order, etc.) as well as safety (how fast system will react to STOP button). Note that the timer is EXTERNAL. Thanks again,

-Alex B.

ladder_2_flow_2.gif
 
I noticed a few things:
1. How will outgoing ram retract?
2. Where is the timer?
3. What exactly is X4? If timer is T0 then the done bit is T0 XIC.

I think Y1 is or should be the incoming ram, was in old scenario.
THIS is a biggie...YOU should never use the same coil twice in a program...ie you Y0 shown in 2 separate rungs, in this case the first run will always keep the ram extended as long as C0 is true.

I did NOT use the CT1 done bit to reset CT1 because I was worried that it would scan that rung and reset the count before it reset the other rungs. I used a timer to delay the reset.

Maybe Eric or someone will clarify if that is actually needed.
BTW I placed C0 in front of everything so I was positive that if the machine was stopped everything would reset. This was a basic move but means that ANY time the machine is stopped you would have to start over from beginning....ie clear bottles off and start over.
 
Last edited:
What the...

I spent about 10 minutes creating a ladder for this problem and 30 minutes trying to figure out how to post it. I'm trying to help, can someone help me help someone else?

AJ
 
Actually I did the same, making the picture fit was the hard part. Make sure the picture is either jpg or gif and is small, I am not sure of exact size limit but I try to stay under 50kb. Then in the reply section where it says Attachment browse to your folder where the file is..hilite it then click open, the file should be listed now, click submit.
 
;)

Rsdoran...

The outging ram should be disabled in rung 5: when timer expires and X4 becomes logic 1, Y0 should become logic 0 (am I wrong?). The timer itself is an EXTERNAL device - I am simplifying it as 2 "leads": Y1, which starts the timer, and X4, which reports timer expiration. As far as the incoming ram - I have removed it (sorry for the confusion). That is, all incoming-ram related rungs are now removed. The double reference to Y0 is w/regard to the outgoing ram only - to extend and retract it. As far as machine safety goes - the C0 is fine. If you have any idea how to make the machine assume a FAULT state when STOP is pushed (retract outgoing ram, go to top of ladder) please let me know. Thank you for all the help, -Alex


AJ...

The easiest way I can see is to screen capture the ladder diagram (push PrtScrn or Shift-PrtScrn) and then open MS Paint or other graphics application, Paste the image and trim it. Then save as a .GIF and post the picture, as we've done here. I look forward to seeing another version of the problem. Thanks, -Alex
 
Ok I didnt realize it was an external timer...why use that if using a plc, better to use all the plc has to offer. The internal timers usually can offer better precision.

Anyway dont use rung 5, put your X4 contact in rung 2 after C0.
 
rsdoran said:
I noticed a few things:
1. How will outgoing ram retract?
2. Where is the timer?
3. What exactly is X4? If timer is T0 then the done bit is T0 XIC.

I think Y1 is or should be the incoming ram, was in old scenario.
alehandler will have to answer these... Looks like he's doing just that as I type this post... :D

THIS is a biggie...YOU should never use the same coil twice in a program...ie you Y0 shown in 2 separate rungs, in this case the first run will always keep the ram extended as long as C0 is true.
Heed Ron's double coil advice, but it's the second rung that will override the first rung. Notice, Ron, that if the timer is expired, Y0 will be OFF when the outputs get updated. alehandler's program may actually work, but the first rung becomes basically useless.

I did NOT use the CT1 done bit to reset CT1 because I was worried that it would scan that rung and reset the count before it reset the other rungs. I used a timer to delay the reset.

Maybe Eric or someone will clarify if that is actually needed.
I think you can safely use the 'done' bit to reset the counter in this scenario. I'm pretty sure the 'done' bit will wind up resetting the counter on the following scan. As far as I know, the counter looks at the state of it's inputs (increment and reset), and the 'done' bit goes on AFTER the counter's rung is finished (so the reset WAS off when the counter got scanned).

BTW I placed C0 in front of everything so I was positive that if the machine was stopped everything would reset. This was a basic move but means that ANY time the machine is stopped you would have to start over from beginning....ie clear bottles off and start over.

More good advice from Ron. It can't hurt to add an extra contact even if it works without it. You never know what changes a future programmer might make.

beerchug

-Eric
 

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