Help on ladder diagrams

A temperature control system consists of four thermostats controlling heating units. The thermostat contacts are set to close at 50,60,70, 80 degrees F respectively. The PLC ladder logic program is to be designed so that at a temperature below 50 degrees F, three heaters are to be ON. Between 50 to 60, two heaters are to be ON. For 60 to 70, one heater has to be ON. Above 80, there is a safety shut-off for all three heaters in case one stays on due to malfunction. A master switch is to be used to turn the system ON and OFF. Prepare a typical PLC program for this control process.

A pump is to be used to fill two storage tanks. The operator from start/stop station manually starts pump. When the first tank is full, the control logic must be able to automatically stop flow to the first tank and direct flow to the second tank through the use of sensors and electric solenoid valves. When the second tank is full, the pump must shut down automatically. Indicator lamps are to be included to signal when each tank is full. Prepare a typical PLC ladder diagram and program for this control.

Help is greatly appreciated.

How LAZY do they get?

For Question One:

- What should happen between 70 and 80 degrees?
- The number of heaters is specified. Does it which heater is on (i.e., when there is only one on, should that one be different every time?)

I'm done with Question Two. Where should I email the solution to get it graded?

Received via Private Message

sandya_116 wrote on Today 04:25 PM:
Can you please email me at sandya_116@yah**.*** Thanks.

Click to expand...

(email addressed edited for privacy)

I'm sorry, Sandya, but you must have misunderstood me. I want to have MY work graded and count for ME. I don't want to have YOU turn in MY work and receive credit for it. I was looking for the email address of your prof/tutor.

---

Now, if you are really interested in HELP, your first task:
POST THE I/O LIST FOR EACH PROBLEM

Is it just me and my evil ways or does anyone else feel like reply posting the incorrect answers / homework to some of these???????????????????????


bonkhead

I guess it's my turn to bemoan the State of the Student

I tried it once (CLICK HERE ). It doesn't help. (although it sure felt good at the time)

I had a professor in college who would sometimes give out the wrong answer to students, just so that they would take that answer, continue on with the derivation, and come to such a rediculous conclusion that they KNEW that it was wrong.

He was pretty much universally reviled by students. The students didn't learn the right answer, they just learned not to ask him any questions.

That's not what we want. Whatever else this site might be, it is first and foremost "Your Personal PLC Tutor". We want, or at least should want, students to feel free to post questions here, especially ones that the tutorial and Phil's book don't answer.

But students being who they are, they usually just post their homework and then say "Help me". The problems are usually trivial for those of us with more than a few years of experience, and can be done in our heads in minutes.

It becomes tempting to simply post the answer (especially since, as Terry so rightly put it in the New Here?, we usually have starving egos which need to be fed) and let it go at that.

But posting the answer is wrong too. Sure, when they see how it's done, a light bulb will go off in their head. But the light will be relatively short-lived. They need to be guided into "How to Think like a PLC Programmer", which requires a very specific, very exacting mindset.

The only way is to guide them through it, step by step.

But what normally happens is that the student doesn't wait for each step. They usually either A) Never follow up with even a second post; or B) Solve it themselves without our help. It's a rare student who comes back, and really listens to what we have to say.

Which is too bad. When they do listen, they get so much more than what's in their text book or lectures. But that's the way it is. If you don't like it, you don't have to be here.

I can't stop you from posting bogus code. Nor will I spoil your fun if you do. With Sandya, here, I was deliberately trying to hook her(?) with the promise of done code. And I do have a working solution, to both problems (The first problem is 5 rungs long, the second is 3 rungs). But I'm not emailing them anywhere (I don't need the 'A'). But I'm willing to guide her to them, step by step, until she not only has the solution, but can do it on her own, by herself.

If she wants it.

Students will try your patience!

Since I left the work-a-day world of industrial controls and such, I have been impressed with some students and appalled at others. My methods in class are not always orthodox but one thing I strive for is that sense of guiding someone through a concept and not simply doing an example and then saying "do it like I showed you and shut up". I do not want my students to be like me, for that would indeed hinder their future. I want all of them to be what they are and take what skills they can learn in my classes to their respective careers as their own knowledge. As in the case here, if we simply give someone the code, we are letting him or her off to easy plus doing them a disservice.

Without one of us around all the time, they will never be successful at their craft. However, as Allen suggests, if we guide them, then the process may not be pleasant, but it will be more helpful. The unfortunate thing here is that some just want an answer and do not want to work for it. That is sad and I can tell them all that another line of work is in their future, because programming PLCs is not going to be it. You just have to be willing to work at it and become good later if you are lucky. Just like most of us have already done.

Fair play,,


I Mylo promise never to post bogus code for any homework solution however I am not promising anything for my alter ego "Guest" for his demise.


Only joking,
I will endeveour to uphold the good deeds of this site for all my worth,, but it is tempting isn't it!!!!!!!

Knowing my code anyway I would probably have the correct answer wrong...

Cheers,

Mylo

Can someone tell me where I can download a free PLC simulator? I'm not looking for pirated software, and it seems like something likely to be available as shareware of one sort or another. I'd be interesting in trying these problems, as a fun exercise kind of thing..
Also, and I hope this turns out correct, is this possible?

-----[a]-----------------------------(o1)--------

                    |

                    |

                    -------[c]-----------(o2)--------

What I'm trying to do is turn either (o1) or (o2) on, but only if [a] is closed?

[EDIT]
And lo, I look further down the topic page, and the software question is answered.