Flow Chart

Hi there,
I'm getting into PLC programing and I would like to know if there is any basic rules to apply while creating the flow chart, it seems that everytime I create a flow chart, it won't work the way I planed, so I have to perform several changes in the ladder logic, and I want to be able to create my flow charts very accurate on relation to my process, I know that this is part of practices, but if there is any book or any material that may help.

Regards
Erosas.

Figure out every step of your process, or even if it is a "step" process (Some continuous processes aren't easily modeled in a flow chart...)

1. How does the system start?
2. What next?
3. When is this step done?
4. More steps?? If yes, go back to step 2, else continue
5. How does the system know to stop?
6. What does the system do during the "idle" state?
7. How do you detect faults/alarms?
7a. How should the system respond to each fault/alarm?
7b. How does the fault/alarm get reset?



Perhaps if you have a specific example or question we could help better. I've just tried to outline a few of the questions that I go through when programming. Honestly, it's something that you have to learn and you keep improving.

A good flowchart, done and documented well, is not only your best tool when programming, but it's also invaluable when troubleshooting! But the secret is to document, document, document!!

Hi erosas.
I think you must visit the following site for solution of your query.
"http://www.edrawsoft.com/flow-chart-design.php"
Thanks.

If you use flow charts you have to be careful since inputs and outputs change with time, you can try state diagram that is better than flowcharts in PLC programming.

Unfortunately, there is no unified method availabe (UML Unified modelling language in IT programming) for automation in desgin and development. UML cannot be directly applied to automation. if you know about UML, you may document it on your own way with modifications.

To check your program one good way is to use a timing diagram after you program it. The other method is to conduct a simulation.

Regards

Palitha

I have found that by writing things out in sentences helps.

If you can first write out how you want it to work, as if you are explaining it to someone, then it will be an easier program to follow later.

I have heard the advise (on these forums) "write the comments first, then program the rung"

If you are just starting, you may want to investigate Boolean Logic. It is complicated at first but results in flawless efficient logic. (or as close to it as you can come on paper!)

Last bit of advise: Use the "Do > Done" idea.

Example: I want to open a door

Step 1) If door is ready to open then "DoOpenDoor"
Step 2) If DoOpenDoor then "trigger door actuator"
Step 3) When door is open then "DoneOpenDoor"
Step 4) use the DoneOpenDoor bit to turn off the DoOpenDoor bit

When the program stops for some unknown reason, you can look at the logic and easily figure out what went wrong.

Example: DoOpenDoor is on but we never got to DoneOpenDoor, must mean the problem is located in the door mechanisim.

Without the Do > Done, you will spend more time trying to figure out if the program even told the door to open.

Also read this: http://claymore.engineer.gvsu.edu/~jackh/books/plcs/pdf/plcbook5_1.pdf

Programming Sequences is a fairly regular topic. The search facility could provide plenty of material ro read but try this recent thread for starters.

http://www.plctalk.net/qanda/showthread.php?t=45009&highlight=state+diagram

Nick

here is what i do,

write down on a piece of paper the machine sequence i want(without stating any i/o).

then review the instructions, add to if you forgot a step.
then expand on what you wrote by adding i/o
review again.

start with the basics, then keep expanding from there.

regards,
james.