Ladder to logic

hamg81

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Join Date
Jan 2012
Location
MEXICO CITY
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HI, I DON´T REALLY KNOW A LOT ABOUT PLC´S BUT I NEED TO TRANSLATE THIS LADDER DIAGRAM TO LOGICAL GATES.
I KNOW THAT TO PARALLEL CONTACTS MAKE OR GATES AND SERIAL CONTACTS MAKE AND GATES.
SO FAR SO GOOD :cool:, THE PROBLEM IS IN THE FIRST RUNG o_O. ?? (NOT SURE IF I´M USING THIS TERM CORRECTLY...)
THERE IS AN OUTPUT IN PARALLEL WITH A TON... SO HOW IS THAT POSSIBLE? I CAN´T USE THE ONLY OUTPUT I HAVE AS AN INPUT OF A GATE, CAN I??
I HAVE ATTATCHED THE ORIGINAL DIAGRAM AND MY BEST SHOT TO TRANSLATE IT, COULD PLEASE PLEASE ANYBODY HELP ME??

THANK YOU SO MUCH!!

12012012265.jpg
 

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example:

BS-3201-B = start
or
SW-3202 = motor

If you press the start-pusbutton and example the stop-pushbutton is still NC the output SW-3202 will turn on.

After you have pressed the start-pushbutton, it will open again. So the motor would turn off if it did not kept it self high because of the instruction "OR SW-3202"

If you want to stop the motor: you press the stop-button and e.g. BS-3201 will be a logical '0'.

Parallel with the start-button you wire a NO-contact of the output = OR-function

In series with this you wire the NC-contact of the stopbutton = AND-function
 
I don't have to much time at the moment to review the logic is this a working running program in the PLC. You can monitor the PLC IO in real time on most PLC's. Thats a good way to check what in programmers intention was.
 
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Hi, thanks for the reply. I know an output can be used as feed back, what i don´t really understand is how to interpret the output sv-3202 in series with the psl-3218 and te ton´s tt this in parallel with the ton itself and the bs-3201b and the psl-3218.
 
SV-3202 is energised if
- timer120ms (ton?) is 'true'
or
- PSL-3218 is 'true'

timer 120ms is 'active' if:
AND BS-3201
AND BS-3201A
AND PSL-3218
AND the OR-function
are active at the same moment

the OR-function is true if:
BS-3201B
or
SV-3202
are true
 
I CAN´T USE THE ONLY OUTPUT I HAVE AS AN INPUT OF A GATE, CAN I??
Yes, you can. That is a feature that makes logic gates more useful. The output can feed backwards to another device, or back to itself, as well as forward.

This same logic feature is implemented in nearly all PLC software programs. I have seen a few low-end PLCs (advanced programmable smart relays like the ZEN) that had limited feedback ability, or only one output allowed per rung.
 
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