RS logix Ladder Logic question AB1500

Hi everyone, I want to thank the kind folks who have been helping me so far.

I am working on a practice lab, I'll post the picture of my ladder logic first then explain where I am stuck.



I am supposed to have one start button
one stop button.
holding circuit
one motor comes on 10 seconds after PB is pushed and remains on for 7 seconds.
1 green pilot for the motor on and only when it is on.
1 red pilot light always on when the motor and/or the GPL is not on.
if the inputs to the timer go false or if there is a loss of power the timer must keeps it's accumulated value.
once a full cycle is complete the timer must reset automatically.
Cycle stops automatically after the motor stops.

On my simulator I have satisfied all the requirements except after the second Timer starts when I push the stop button the process stops but only if I keep the button pushed in, I need the process to stop and stay false until the start button begins the cycle.

Any sugestions are appreciated.
Thanks again.

I didn't test it but you might try reseting the RES (rungs 4 & 5) with the stop pb also.

Or, you could try separating your holding circuit from the time-on delay. Such as programming the start and stop input to a bit address and turning on the output when the "run" bit is true and the first timer is done.
Also, in many real world applications, the stop button input is wired normally-closed so the output "fails-safe" if a wire is cut.

What you are describing sounds logical but I am trying to picture adressing it by Bit address. A snapshot would help me out alot. This is very new to me and I am learning as I go along.

You can do it with one timer, as mentioned have a holding circuit that enables the cycle that enables the timer. Take a look at the attached pdf and see if it works in your simulator.

ktm said:

What you are describing sounds logical but I am trying to picture adressing it by Bit address. A snapshot would help me out alot. This is very new to me and I am learning as I go along.

Click to expand...

By bit address he means a memory area that is not a physical input or output. By default with an AB PLC there is a B3 data table (you can create more). For a contact or a coil you can use B3:0/0 for example.

N tables are for integers, F for floats, T for timer, C for counter etc....

If you are taking a course your instructor really should have explained this to you before expecting you to write a program?

it's a workbook I am studying at home, self learning.
I understand the table of different default bit files.
I guess I meant to be more specific I am trying to learn to use a status bit file?

Greetins KTM.

Lets have you answer some questions in the hope that answering them will help you make sense of what your program is doing.

Starting with rung 0: When does the bit T4:0/TT become true? How long does it stay true? When the T5:0/DN bit is set, what is the state of the /TT bit? How long does the T5:0/DN bit remain set on a retentive timer?

Rungs 1: There is an unnecessary bit on this rung that might be obfuscating part of the problem in your program. Hopefully you will see it as we move on. More on that in a minute.

Rungs 0,3,4,5: If the timer T4:0 has not timed out, what does pressing the stop button do? What happens to the TT bit? What happens when the stop button is released.

If T4:0 has timed out, then what does pressing the stop button do? What does it do to timer T4:1? When you release the stop button, then what happens? See how the bit T4:0/DN is still set, so what does the output at O:2/0 then do? And how does that affect timer T4:1? How does pressing the stop button affect rung 1? If you understand what is happening now, can you see how it makes the lights turn off, making you think you have stopped the process, when in fact, you have only interrupted it?

Hopefully if you answer those questions you will see why your program doesn't work.

By now you are probably wondering how to make it work. Lets
start with a basic seal in using an internal bit from the B file.

     I:1/0      I:2/0       B3/0

-+---} [----+---]\[---------( )---

 |          |

 | B3/0     |

 +---] [----+

 

Now you can take this bit, B3/0 and use it in your program

to trigger other things, such as timers, outputs, etc.

 

eg:

   B3/0

---] [--------------------?????

 

Now see if you can construct a working ladder that uses only the timer DN bits to drive outputs and resets. Place the output bits as the last rungs in your program.

my second attempt proved to be an improvement in logically continuity. I have satisfied all of the requirements involving the stopping/ interupting and restarting the process.

My final step is the cycle must stop automatically when the motor stops after the 7 seconds.

in my program after the final rung the cycle begins and starts the first timer again.
I would like to figure out a way to make sure the cycle only starts again when I manually start it.

Rung 000 add NOT T4:1/DN

TY that satisfied all the requirements. I was still thinking electrically not logically.
Ya'll are the best for helping out a fng.

No problem, now explain what you are doing, especially with the resets before the timer.

While at it explain fng.

rsdoran said:

No problem, now explain what you are doing, especially with the resets before the timer.

While at it explain fng.

Click to expand...

Flippin new guy?

allscott said:

Flippin new guy?

Click to expand...

Thought something along those lines, just checking.

After sleeping on it I decided to rewrite this a little.
The problem I think I wasn't comprhending was the proper use of the TT/EN/DN bits.