Sample Applications to get started

[tcpdump]

Hi, Could anyone suggest some basic, simple examples of programs/applications I could develop to start learning about PLC programming? Thanks, tcpdump

[TimWilborne]

We joke about them when student come asking for us to do their homework, but stoplight, washing machine, and elevator programs are some of the best to start learning. Everyone is familiar with them and they teach you the basics of inputs, outputs and how to sequence them based on external conditions.

[Ken Moore]

My favorite is the washing machine. You can start simple, just a wash and rinse with a set time. Then once you get that, you can add soak, spin, etc.. variable water temp. and level. More and more complicated just like the latest models.

[Guest]

have you worked through the ones (or similar examples) at www.thelearningpit.com? ...

[tcpdump]

Umm, I meant a bit more low level than elevator, washing machine etc.. e.g. a timer that resets after 10secs a stopwatch, with start, stop, reset, dual time

[Ken Moore]

Okay here's a real world application, that's real easy. I normally do this with a PICO smart relay. You have a 20 HP 480VAC 3 phase, storage tank agitator that is started and stopped via a standard NEMA size 2 motor starter. Two normally open momentary push buttons, one named start, the other stop/reset. You have one indicator lamp. The agitator needs to run for 10 minutes, then be off for 50, run 10, off 50 etc... If the agitator is commanded to start and the aux. contact on the motor starter does not pull in within 5 seconds, then the indicator light flashes on and off to indicate a fault. If the aux. contact does pull in then the indicator light comes on steady, to indicate running. Anytime the "start" PB is depressed, the agitator will run for 30 minutes, then wait 50 minutes, and run 10, and continue the normal auto run time. If the agitator is faulted, depressing the stop button clears the fault. If the agitator is running, the stop button will stop it, and the 50 minute off time will begin. How's that? Real world. Simple. If I forgot a detail, just let me know.

[OZEE]

Those are great examples that you have suggested yourself. Try them -- if you need help, post what you have, ask specific questions, then we can help. We won't do it for you, but we'll help. The elevator, stop light, and washing machine applications are very typical samples that are used in training classes. They are very simple applications that we are all familiar with. Ken's agitator suggestion is also a very simple, real life application. The way to learn to program PLCs is to FIRST - before you do anything else - define what you want your system to do. This can be a flow chart, a sequence of operations, an outline... whatever it takes to define your system. Answer questions like "How does it start?" "How does it stop?" "What happens next?" "What if there is a fault?" "How does it restart?" "How does it reset?" Then -- AFTER you've defined your system -- you can start defining the hardware required to meet your requirements. PLC, I/O, communication networks, HMIs, etc. While you're doing this phase, make your system drawings and document all of your I/O. Then you can start programming. It doesn't matter what your system is -- it can be a stop watch, an elevator, a stop light, a blending system, an oil refinery.... The process is all the same. With practice, you might just do some of these steps in your head on a small project, but you still need to go through the process. I've been doing this for 20 years and still do it this way -- every time! So, for your stop watch: 1) How does it start? 2) How does it stop? 3) How many timers do you want/need? 3a) Do they need to run concurrently, independently, consecutively, whatever...?? 4) How do you reset the timer(s)? 5) What other information do you need to be able to completely define this application...???? See what I'm doing?? Try answering those questions here... we'll be glad to help you if you miss something or get something wrong. Then you can move on with the "How to do it" questions, then on to the actual code.