ladder diagram

[Anirban Hazra]

@Lancie
Sir mine was a general drawing and my mistake was that I had left it to the intelligence of the beginner to understand the logic and implement it correctly with appropriate modifications in his/her respective PLC rather than exactly reproducing my drawing without understanding the logic behind it because if the beginner is at a level such that he/she does not know that in his/her software every rung requires at least one output rung, then he/she wouldn't be at a level to understand this logic anyway.

Also maybe it is how I was trained because when we were being trained it was always stressed to understand the concepts behind the functions rather than just trying to mug how they were addressed or placed because those could be figured out in no time for each PLC/software and because the Logic behind the program remains the same and only the "syntax" changes.For example,the trainers would just use an NO symbol with upward arrow within it like in Mitsubishi to indicate Rising Trigger in his drawings and we would figure out the modifications. So, that corrected version is exactly what I had meant by my initial drawing because how could I have tested my Logic without using OSR correctly?

Sir,please do not see my replies as arguing but as only efforts to clear myself up to you because I believe it will be many years before I can even think about arguing with people a experienced as you.
​

 

[Lancie1]

Okay, good, everything is cleared up, everyone is happy, and we can go on our merry way.

 

[mag176]

Lancie 1


I am back
here is the image with this logic using only no nc contact and coil..
and it works...

hope you like it
and i think no nc contacts and coils are same for all plc so it will work on any plc


Push button is my input lamp is my output
and int_bit1 and int_bit2 are internal memory bit in plc...

now if you hit push button once lamp will on
if hit again lamp will off...

thanks

 

[daba]

I for one do NOT like it.

Certainly on ALL Allen-Bradley PLCs, SLCs, and Logix5000 systems, (and possibly many other manufacturers), this toggle DOES NOT retain its ON state if the processor is restarted e.g. following a power-cycle, or if the operating mode is changed to PROG and back to RUN.

i.e. the state of the toggle bit can be influenced by something other than the program code, and therefore it cannot be relied upon. In fact in many situations, this "external influence" could lead to dangerous conditions.

The program MUST have control of the state of the toggle bit. It cannot know that it was ON when the power went off, so it is up to the programmer (you) to program the code so that toggle bits are retained. Of course, having done that, it is up to the programmer to decide which toggle bits should be reset upon a processor restart. That is the only "safe" way to handle toggle functions.

Here's my favourite for a toggle. The Counter increments on each press of the button (it has its own "one-shot" on the Enable-In). The Accumulator value alternates between odd and even, so bit 0 alternates ON and OFF.

The counter is a "retentive" instruction, not affected by power-loss or mode-change, so the toggle always retains its state.

 

[Liam Moran]

What happens when the counter accumulated value reaches the maximum?

 

[Mickey]

What happens when the counter accumulated value reaches the maximum?

It rolls over to negative and counts back to zero and starts all over again.

http://en.wiktionary.org/wiki/take_a_licking_and_keep_on_ticking

 

[daba]

Allen-Bradley counters just roll over from 32767 to -32768 (PLC/SLC), or 2,147,483,647 to -2,147,483,648 (Logix5000), and continue counting in the positive direction, forever.... just ignore the OV (Overflow) bit. They never stop counting.

In other systems, it may be necessary to reset the counter when it reaches 2, so effectively counting 0,1,0,1, etc.

HTH

 

[daba]

0111_1111_1111_1110 = 32766
0111_1111_1111_1111 = 32767
1000_0000_0000_0000 = -32768
1000_0000_0000_0001 = -32767

bit 0 (in red), just keeps on flipping !

 

[mag176]

daba
you are right
there are lots of way to do this and it depands on process and requirements..
i made this because
i want to try it only with contacts and coils...

 

[Lancie1]

i want to try it only with contacts and coils...

Mag, I tried out your program on the LogixPro simulator. On the first press the output went on. On the second press it went off. On third press, it did not come back on. Maybe it only works on certain PLCs. The results are attached in 3 pictures.

Here are four additional methods using only contacts and coils, out of 11 that I have collected. The first method uses 1 rung, the next 2 methods require 2 rungs, and the last Method 11 really only needs two rung branches added to existing logic for two motors. You might call that two half-rungs. The timers are not used for the alternator but to stop the motors for testing purposes. These methods are not retentive through power outages (unless you use a PLC that has certain retentive memory areas), so they are safe for student use and training purposes.

 

[mag176]

Lancie

THanks for sending me other methods
its great

but when you tried my logic you forgot to put no contact for push button in rung 2, may be thats why it works only once..
if you make it exact same like i did it will work

please chk my logic again

 

[mag176]

Hats off lancie
you are damm good..
thanks
i will test all your logic

 

[Lancie1]

Mag, I tried to find a modified version of your program that works when tested. This tested versions seems to be the closest to your earlier program.

 

[Lancie1]

but when you tried my logic you forgot to put no contact for push button in rung 2, may be thats why it works only once..

Okay, I see my error now. I apologize. Yes, it does work just dandy.