PLC Rookie

[Stationmaster]

The 'no longer present' part got me too. But it's just another bit of logic to add to the latch or seal-in part. PLC tutorials are to be found by the bucket-load over the net. All of my problems I've solved by 1) RTFM, 2) scour the net and 3) post it up. Very rarely have I needed 3), since most of the time somebody else has already had the same issue and I can read the tips he got.

Agreed. I just thought it was ironic that everyone was lamenting how SIMPLE the circuit was, while at the same time failing to mention the unusual condition of not having the lamp light until the momentary signal was removed.

Kind of like saying "du-UH-uh" when you aren't giving the correct answer. Ironic.

Clay, a motor start circuit starts the motor when you PRESS the start button, not when you release it.

 

[Clay B.]

Agreed. I just thought it was ironic that everyone was lamenting how SIMPLE the circuit was, while at the same time failing to mention the unusual condition of not having the lamp light until the momentary signal was removed.

Kind of like saying "du-UH-uh" when you aren't giving the correct answer. Ironic.

Clay, a motor start circuit starts the motor when you PRESS the start button, not when you release it.

Yea I saw that but I figured he might need to understand exactly what a latch does and to me a basic motor circuit is a good example and there are lots of examples on the internet.

 

[Liam 28]

heres a circuit i have drawn of what you are asked to hope fully this will help to visulaize what you are asked to do see can you convert this to ladder logic i presume its ladder logic your asked to program it in.Hope it helps

Liam

 

[Paul B]

The intent of the members here is to encourage people to learn, and not just give out the answers. This poster is having trouble "seeing" so I will try to help.

Take it one step at a time. With word problems it helps to break it down

"a momentary input signal existed at one time"
The definition of momentary means came and went. A latch has already been mentioned to store this state.

"turn on a light"
So turn the light on.

"a momentary input signal existed at one time, but is no longer present"
Don't turn light on unless the momentary input is gone

"An acknowledgement, a momentary pushbutton will turn the light off"
Something has to reset that latch.

 

[PhilipD]

No textbooks? No instructors? No resources? Then you can't learn it. Poking around is not the way to go.

Wrong! Someone had to invent this stuff and they did it without textbooks, instructors or a structured course. Da Vinci was a great artist and inventor with no formal education. Charles Babbage is credited with inventing the computer (differential engine) in the early 1800's. Again no books were available on this subject for him to reference. There are many, many more examples we could all think of.

Now, I don't propose that learning without any help is the best way at all. I would really like to be able to go to school for this or to shell out a few hundred dollars for a course but that is not to be at this point so I am doing what I can. I search for examples, I ask questions in forums like this one and I read the RSLogix manual. I welcome comments and advice from anyone who is willing to offer CONSTRUCTIVE help. If all someone can contribute is to suggest looking (searching) elsewhere then they are no help at all. Look at it like this, if everyone searched the internet and found an answer on another site then there would be no reason for this one to exist. Soon no one would come to this site because they are told to go look somewhere else then the only ones left here would be you and Shoelesscraig.

My point is either help or don't reply. And please don't ask folks to look somewhere else.

 

[TimWilborne]

No textbooks? No instructors? No resources? Then you can't learn it. Poking around is not the way to go.

I'll have to agree with Phillip here. Some people learn well by textbooks, instructors, and resources, others don't. I pretty much learned by poking around

 

[Paul B]

I'm completely self-taught. I worked in a plant and built my own relay logic controls for five years and when PLC's began to come in I followed other people's code and saw how they did things and it took off from there. Now its what I do to provide for my family.

The thing about word problems - what was originally posted - is not everyone can read words and see the picture they represent. Hands on training and some tidbits of example code (even if it means giving away the answers) will do a lot to help new people come into the field.

heres a circuit i have drawn of what you are asked to hope fully this will help to visulaize what you are asked to do see can you convert this to ladder logic i presume its ladder logic your asked to program it in.Hope it helps

Liam

Liam, thanks for posting that... it was a different way to solve the problem and I appreciated seeing it.

 

[Paul B]

Self motivation is paramount to learning on your own. If you are interested and want to figure it out, you will.

 

[KP_EENG]

I am all for helping people to learn to program, but the problem arises when students come to this website asking for answers to homework problems without trying or barely trying to figure it out. If we just give them the answers then we are perpetuating their inability to solve problems, laziness or whatever there issue is and we are not helping them learn to solve problems, just regurgitate another person's work. Furthermore, what about the students in the class who do the work on their own? It certainly isn't fair to them.

Regards

 

[TimWilborne]

I am all for helping people to learn to program, but the problem arises when students come to this website asking for answers to homework problems without trying or barely trying to figure it out. If we just give them the answers then we are perpetuating their inability to solve problems, laziness or whatever there issue is and we are not helping them learn to solve problems, just regurgitate another person's work. Furthermore, what about the students in the class who do the work on their own? It certainly isn't fair to them.

Regards

Agreed, but I think Mickey's response was all that was needed then wait to see what he came back with. You know he's probably not coming back now

 

[Stationmaster]

The intent of the members here is to encourage people to learn, and not just give out the answers. This poster is having trouble "seeing" so I will try to help.

Take it one step at a time. With word problems it helps to break it down

"a momentary input signal existed at one time"
The definition of momentary means came and went. A latch has already been mentioned to store this state.

"turn on a light"
So turn the light on.

"a momentary input signal existed at one time, but is no longer present"
Don't turn light on unless the momentary input is gone

"An acknowledgement, a momentary pushbutton will turn the light off"
Something has to reset that latch.

TAA-DAAAAA....

The circuit must FIRST be understood....... verbally ...... before you can start to program. This is PROBABLY the most important lesson we could hope to teach the OP at this point.

Stationmaster

 

[Mbeavers34]

Some great thoughts. I have really enjoyed this thread. My normal gig is a college instructor, electronics, PLC and HMI programming. I do consulting on the side and took a sabbatical this year to do the automation programming for a plant that is just starting up. I too, am pretty much self taught. Did do an allen bradley training, but pretty much that was just how to operate their software. I've seen students do everything under the sun in order to not spend any time in order to get a grade. So, I can understand those who want to see them do some homework before before they post some basic questions. I also agree that this forum 'IS' research for some students as well.
A little while back someone suggested that this forum have a special 'student section' .
Can you image how helpful that could be? Imagine having some of the basic concepts being explained by several of the great minds and personalities that post here.

Michael

 

[Mickey]

A little while back someone suggested that this forum have a special 'student section' .
Can you image how helpful that could be? Imagine having some of the basic concepts being explained by several of the great minds and personalities that post here.

Michael

That is the whole premise of this site. You just posted in the student section.
As said in another thread "we are all students".
Look at the top of this page. See picture below.

 

[TimWilborne]

Can you image how helpful that could be? Imagine having some of the basic concepts being explained by several of the great minds and personalities that post here.

That was pretty much the premises behind Ron's Patchn. While it's forums are all but dead, it's article section is tremendously popular, especially among students. Feel free to submit articles to it that you feel students would like
http://www.patchn.com/index.php?option=com_content&task=section&id=4&Itemid=74

 

[PhilipD]

OK, I tried this exercise. First I used two NO MOM PB. One PB would latch an output on. The second PB would unlatch the same ouput. Easy Peasy! Then I figured the original problem was to use only one PB. So I had one rung use the PB (I:1/0) to latch an output. Then the second rung used the same input to unlatch the output. Didn't work.

Then I had one of those A-ha moments: if the light is on turn it off, if the light is off turn it on. So I had a rung with a PB, then I used XIO to see if the output was off, if so latch it in. Below that I added a branch using the XIC instruction. If it was on unlatch the light.

It didn't work. I thought the PLC would scan the program, find one true condition (light on or off) and take that branch while ignoring the other branch. I guess that is not right. I think it still scans both branches even through there is only one rung.

More thinking to do.