Timers, Counters, Comparing, a simple program_need advice

[neokeelo]

Hi. I am working on my 6th assignment. I have a better understanding of timers, counters, compare and the limit command but I am having trouble getting them to talk to each other.

Here is my program
-------------------------
Basically there are 3 process that need to run for a specified time, turn off and the next one start, repeat 4 times and stop and reset everything at the end.

Button one ( I:1/0) starts the process.
Filling = 3 secs O:2/0
Heating = 5 secs O:2/1
Draining = 4 secs O:2/2

Rules
I can use the comparison instructions and only one timer in the program. Also Only one counter can be used but not the counter DN bit.

Here is what I have so far. I know I need something on RUNG 6 but i dont know what. What am I missing to complete the program? Any advice is appreciated!

[Longhorn]

First of all, remove the counter and the counter reset on rungs 1 and 6. Before youre timer reset put a compare >= 1201 with T4:1.acc, this will reset the timer once draining is complete. Last of all, increase your timer value to 1250 or summit.
Just a tip, i would use a retentive timer for T4:1 so that if the PLC is put into stop or in the real world an error occurs, then ot wont start trying to fill if it failed in the draining stage.

Hope this help.

[bernie_carlton]

1. Rung 0 - place a NC (XIO) of C5:0/DN on the rung to reset it once the counter is done.

2. Rung 1 - Place a NO (XIC) of I:1/0 on the rung to reset the counter while the button is being pressed.

3. Rung 2 - Place a NC (XIO) of I:1/0 in the rung to prevent the timer starting until the button is released

4. Rung 6 - Place a NO (XIC) of T4:1/DN on the rung to trigger the counter as the timer finishes

[Mfleming]

1)Need NO operands before CTU and RES in order for them to work properly. Wthout operands the count will count once and reset once per scan thus not retaining a value.

2)Add a NC CTU.dn to the start rung to stop operation when count is done.

[neokeelo]

thanks, ill make some changes and do some testing and post something later.

[leitmotif]

It is somewhat unrelated to your assignment I admit
BUT
Since I forgot to design how to stop a machine and embarassed myself (only once I think ??)
I believe it is a good part of design to have a stop function.
Since you say
Button one ( I:1/0) starts the process.
and appears to be a momentary I would add a NC stop button in the start circuit.
As another post points out how is the process going to know where to restart if it is interrupted? This is a real world concern and may be beyond the intent of the lesson but you will need to think about this stuff in the future so you may as well start now. Maybe you will even get extra credit.
Dan Bentler

[ATU]

In my opinion, you are not really helping this guy out, by just telling him what to change. He needs to figure it out for himself. What would be better is to tell him that a specific rung is wrong and let him find the mistake or if he has a specific question about how something works. After all, he might be working for you someday.

[neokeelo]

I understand your point, but with all due respect, I am spending hours trying to write these programs. In our class and in the book there are NO examples problems we can look at and study to better understand the commands and how to use them. In this particular problem I understand the logic ( what needs to be done and where to put it) I just don't have any experience with these new commands yet and know how to get them to talk to one another. Looking at other people's programs seems to help the most I think.
thanks

[Tharon]

Well, since you are not allowed to use the DN bit of the Counter, you need to understand what the DN bit is.

The DN bit is true if the Accumulator (ACC) is greater than or equal to the Preset (PRE). Using this you can rig yourself up a Bit that does the exact same thing as the DN bit.

[zankorel]

Originally Posted by ATU

In my opinion, you are not really helping this guy out, by just telling him what to change. He needs to figure it out for himself. What would be better is to tell him that a specific rung is wrong and let him find the mistake or if he has a specific question about how something works. After all, he might be working for you someday.

I think it is fine for people to give their opinions on how he could improve it as it is obvious that the OP has attempted it to start with. Any feedback is only going to improve his understanding of PLC's because he has done the groundwork already.

If the OP had just asked for information on how to do it without trying it himself, I would agree with you.

[milldrone]

Originally Posted by neokeelo

Looking at other people's programs seems to help the most I think.
thanks

Ahh!!

How about this then?
http://www.plctalk.net/qanda/showthr...beginner+cycle
Or this one?
http://www.plctalk.net/qanda/showthr...beginner+cycle
This does not match you specs but there is some good stuff here.
http://www.plctalk.net/qanda/showthread.php?t=25856

[ATU]

In our class and in the book there are NO examples problems we can look at and study to better understand the commands and how to use them

If you don't understand something, post a question and I am pretty sure you'll get 10 answers within a few hours with examples.

[leitmotif]

Originally Posted by neokeelo

I understand your point, but with all due respect, I am spending hours trying to write these programs.
REPLY So did we. So do we -- still.

In our class and in the book there are NO examples problems we can look at and study to better understand the commands and how to use them.
REPLY That is going to be an ongoing problem. Therein lies the challenge.

In this particular problem I understand the logic ( what needs to be done and where to put it) I just don't have any experience with these new commands yet and know how to get them to talk to one another.
REPLY Again there is the challenge. There are numerous posts in this site on just this issue.

Looking at other people's programs seems to help the most I think.
REPLY Well it is the quickest I agree. But will you remember it next week if it is handed to you?

thanks

REPLY You are welcome.