Reverse Engineering

[GlenGineer]

To write the functional design specs. I would start by getting a copy of the specs for another machine. This will give you a format to use. Next I would get a copy of the electrical schematics. The electrical ladder gives you a ton of information.

If you were designing this program from scratch you would start with the customer specs, a drawing, electrical ladder, IO list, and then you start programing. So that be a fair place to start for reverse engineering the design.

The first piece of equipment I designed was an elevator. I wasn't super disciplined when I designed it so instead I wrote a story. The story of how the machine will work. Perhaps a good starting point is to figure out the story of how it does work. Ask the operator about the machine cycle. "It does this then it does that. Unless you are doing this other thing." Next sit down with your story and your electrical schematic and figure out how the story is written in ladder. (I hope it is ladder anyway). As Ron said once you get into the program often you start with outputs and then figure what triggers that output.

Good luck. Have fun!

 

[papejo]

from my little experience:

first thing is to talk to the operator, the operator boss, ask about the machine.

second is look for what brand is the plc., how many inputs and how many outputs.

third is to look for a similar machine and see how it works, to identify sensors and actuators.

then start making your own diagrams, notes if possible , start following cables to make the diagram of the panel, stating from ac source , protections , contactors, sensors etc.



it looks scary but once you have the diagram is all good

 

[cardosocea]

In a few months there will be few who know that machine better....Except the dude who coded it!! Good Luck

Unless the dude that wrote the program is still doing the same thing, or upgrading that same program he may be just a little ahead of where you were when you started. Hence why comments are a necessity... I put comments in whatever I do because I want to know why I did it, not whoever is going to look at it after me.

 

[PLC Apprentice]

Thank you for all the responses guys really helping with the forums and im getting on better understanding how it works. slowly getting the hang of it and understanding the Chronological order the PLC works I have until October to complete so plenty of time to perfect it

 

[cardosocea]

Thank you for all the responses guys really helping with the forums and im getting on better understanding how it works. slowly getting the hang of it and understanding the Chronological order the PLC works I have until October to complete so plenty of time to perfect it

Do give us some feedback on how you get on. It's nice to help, but it's much nicer to know we made an actual difference to the end result.
In this case it is particularly satisfying to see two people that I assume are of a similar age taking a similar challenge completely differently in the forum and the difference in treatment received too.