Help!!!

[atifplus]

I have about 50+ pages of ladder logic and i am trying to understand what is going on. Any tips how I should translate it into some sort of flowchat.

I dont wanan post it here and get people help because than i wont learn .. but i just need some suggestions ..


Tough part the operation is unclear as lots of changes has been done to the old logic with no documentation + comments on the tags are not there anymore.

All i could think of tracking Inputs and outputs related in the operation then organize them in some sort of sequence ..


any tips would be helpful

thanks

 

[Steve Bailey]

Do you know anything about the machine the program is controlling? People tend to write the ladder logic in the same order as the product passes through the machine. If the program follows that model, then the logic controlling the infeed will be earlier in the program than the logic controlling the discharge.

Figure out which addresses represent physical inputs and outputs and which addresses are internals.

Internals that are used repeatedly on many rungs probably represent global permissives while internals used on one or only a few rungs probably represent conditions specific to a single output or sequence step.

 

[atifplus]

it is kind of strange maybe i am not use to this programming style

The output status is stored in internal coil then there and bunch of conditions bla bla

then there are those push buttons and other controls at the very end that activate those outputs ..

i like inputs first then condtion then output .. wonder why they do that this way..

& yeap i am going to talk to operator about how he operates those machines then i wil track down the inputs maybe that would be faster then i will chekc with the logic + ( I will figured out how well operators knows) maybe that is the way to go

 

[davev]

Do you have an electrical drawing? Or some other way to identify the inputs and outputs. Start by documenting the inputs and outputs before making any atttempt to understand the internal bits and timers ectera.

Did you say just modifications were not documented (labled, descriptions, comments) or that nothing at all was documented in the program?

Another usefull tool is to be online and monitor things while system is in operation.

If somethings are documented in program (or on electrical drawings) and then you talk to operators: be prepaired for the operators (or any/everyone else) to call the devices by different names than what was on the documentation.

About the output status (as you called it) and then the other logic before making actaull output - - maybe that is all related to the auto mode logic and the hand mode button/switches. Just a quess. Again, start by documenting/labling/commenting the inputs and the outputs before trying to understand any of it.

 

[atifplus]

Thanks guys

Seems like it is not going to be easy there is some hardwire stuff linked to PLC though relays. Must find those electrical drawings.

Wish me luck

 

[BobB]

The output status is stored in internal coil then there and bunch of conditions bla bla

then there are those push buttons and other controls at the very end that activate those outputs ..

That is quite common.

Get the drawings and tehn type in the tags for the inputs and outputs. That is a good place to start.

 

[milldrone]

Tough part the operation is unclear as lots of changes has been done to the old logic with no documentation

If you were an integrator, this is when you would start swearing. But because I think you are a inhouse programmer/end user, this is when you get to "look over someone's shoulder". This can be a great opportunity to see how someone else would solve a problem. It is also a yard stick to measure yourself against someone else. When you are done figureing this machine you will be in a good position to make changes or improvements.

wonder why they do that this way..

Ahhh! Grasshopper! When you know the answer to this question you are well on your way.

 

[atifplus]

haha thanks for motivation

 

[Eric Nelson]

After you have all the I/O filled in, the next step would be to look for any 'special purpose' bits unique to the processor. Things like 'always on' or 'always off' bits, clock bits, etc., etc...

Good luck!



-Eric