One method of the PLC programming is using ladder
diagram method. Ladder diagram consists of a descending line on the left, with
lines branching to the right. This line is the line branching instructions.
Throughout this instruction line consists a combination of logic that states
when and how the existing instructions on the right side are done.
Ladder Diagram Example
The logic
combination of ladder diagram as following:
A. Instruction
LOAD (LD) and LOAD NOT (LD NOT)
The
first condition that starts any logic block in the ladder diagram associated
with LOAD instruction (LD) or LOAD NOT (LD NOT). Each of these instructions
requires one line of mnemonic code.
B. Instruction
AND and AND NOT
If
two or more conditions that are connected in series on the same instruction
line, then the first condition using LD or LD instruction and the remainder NOT
use the instructions AND or AND NOT.
AND
instruction can be imagined to produce ON if both conditions are linked with
this instruction in all ON conditions, if any one in the OFF state, let alone
both OFF, the instruction will always result AND OFF too.
If two or more conditions connected in
parallel, meaning in a different line of instructions and then joined again in
the same instruction line, then the first condition associated with LD or LD
instruction and the rest is NOT related to the instructions OR or OR NOT.
In
this case imaginable OR instruction will always result in ON execution
condition when any one of two or more conditions connected with this
instruction in the ON condition.
