i need help like asap

[iamtheville]

this is what i have from class today

 

[iamtheville]

heres a better pic

 

[iamtheville]

well all im asking for is help. @firejo

 

[Firejo]

I can’t really see the image very well but here are a couple of comments from what I can see.
Rung 0: you have inputs (Red_light, Green_light) on the output side of the rung. You can’t have an input after an output (sump_pump).
Rungs 002 and 003: There aren’t any inputs so the green light and red light will be on all the time (if the PLC will even accept the rungs that way).

 

[iamtheville]

for the life of me i cant figure out how it would make sense if i put an e stop in front to kill all the outputs but a stop is nc would you use a relay with no contacts to keep the light green if its not going? i want to learn and im going to ask a lot of questions if youre willing to read. as long as you can put it into laymen terms. and thank yall for letting me know i have to learn it. so teach my fearless leaders.

 

[iamtheville]

I can’t really see the image very well but here are a couple of comments from what I can see.
Rung 0: you have inputs (Red_light, Green_light) on the output side of the rung. You can’t have an input after an output (sump_pump).
Rungs 002 and 003: There aren’t any inputs so the green light and red light will be on all the time (if the PLC will even accept the rungs that way).

i didnt finish those two rungs in question but i posted a question cause im trying to figure this out

 

[Ken Roach]

At least you've got the basic components and instructions down on the page. That's a start.

FTTH gave you a good explanation of how the functions of a basic relay-ladder logic rung are developed, and how branches and boolean instructions perform if/then/else functions.

Firejo gave good advice about how RSLogix 500 (the editor for the MicroLogix "brick" controllers) requires you to place input and output instructions. Outputs have to be on the right side, and nothing can come to the right of them.

I will add a couple more:

The E-Stop is, as you said, hard-wired. While you can use a status contact as a PLC input to unlatch and reset your program, the actual source wire to the output terminals of the PLC has to pass through an e-stop button (more commonly a safety relay). That's a basic truth of automation: general-purpose software should never be used for safety purposes.

The function to sound a horn if the wire to the high-high level sensor is broken is another basic principle in automation: sometimes a broken wire needs to be detected, and the simplest way to do so is to use a normally-closed sensor.

Under ordinary circumstances, the High-High switch has a normally-closed contact that supplies voltage to a PLC input, so the PLC input data table point for that sensor is True (we also call that logic state High, or 1).

If the wire breaks, the input point goes False.

So how do you tell the difference between a broken wire and the actual High-High float switch being triggered ?

In your case, the easy way would be to check the status of the High and Low level switches. If water is floating both of them and they are both normally-open sensors, then you can deduce that the water level is over the High limit and the High-High switch is probably being triggered.

If either the High or Low switch is False, when the High-High input goes False, then you've probably detected a broken wire.

In real life there are complementary contacts (1 N.O, 1 N.C.) and pulse-test circuits that fulfill this function. But you're in class, so a discussion of likely failure modes and the limitations of simple sensors is appropriate.

 

[Ken Roach]

I take back my comments about deduction of the failed High-High switch. Put in a 'complementary' set of contacts and take advantage of the Timer features of the PLC to "debounce" the switch.

 

[jrwb4gbm]

One way to "Monitor" the E-Stop hardwired circuit is to make the 1st rung of your program like the following.
Use only 1 input with a N.O. instruction and the output MCR instruction.
This does not exclude what Ken Roach said, only to add to it.

Edit:
Another member objected to me posting a sample program in the files section. I will honor the request.
See post#25. Link to post: http://www.plctalk.net/qanda/showpost.php?p=678152&postcount=25

 

[iamtheville]

Thanks fellas. Im going to do most of this saturday cause I don't have work So ill draw out my logic ladder to see if im close but I will have a lot of questions cause I want it to work and moreover I want to understand plc's

 

[xC0MMAND0x]

Its no certificate. Hell I don't even know why they want us to learn this Considering we Don't program plc's in the field. And I can't show nothing cause its on the computer at school. Im just trying to figure What do I put on each line to make this scenario work

What school learned you to talk cause talk like no grammar and punctuation get you nowhere.

</sarcasm>

 

[Lovell]

Who says PLC forums are boring? This is entertainment!​

 

[Drives_Guy_NS]

Funny, as a VFD guy, I see this as more a drive solution than a PLC. But, hey I like to use the K.I.S.S. principle.

Level switch 1 closes, drive starts at one speed.
Level switch 2 closes, drive speeds up.

The complicated part is with the broken wire, but I think I have that figured out too, sorry PLC guys, I don't need you for this one.... ;-)

 

[Manglemender]

Thanks fellas. Im going to do most of this saturday cause I don't have work So ill draw out my logic ladder to see if im close but I will have a lot of questions cause I want it to work and moreover I want to understand plc's

Well done for persevering. You will find much help here so long as you are prepared to make some effort yourself.

Nick

 

[GlenGineer]

I for one feel sorry for iamtheville . From my limited understanding the (US) Federal Governmant has started the STEMS program. PLC programming and automation is part of this. I decided to take a few months off late in 2015 to learn a new PLC programming language and how to program robots. I learned a lot and respected the PLC programming professor but....he was a computer programming professor with no PLC programming experience and only a little PLC programming knowledge. I found the robotics program useful but the professor to be similarly insufficient. As a result the students, myself included, were figuring out how to do things like communicating between PLCs. I expect that in the years to come it will become easier on everybody - both student and teacher. However it might be worse at some colleges. I remember some of the math professors I had at the University of Alabama at Huntsville ( a respected Research University) Some were great teachers however some were so bad that most of the class failed. Hopefully the teaching will meet up with the need for students.

Like many of you I would love to help somebody to learn the concepts but I hate the idea of helping somebody cheat (meaning repeat without learning or asking other people to do your assignments).

I'm both a teacher and a student but if you have questions on concepts feel free to ask me.