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Indra Nisja
Typical PLC Input Scheme
Typical PLC Output Scheme
Rule 1. Input devices are placed on the left corner of the rung.
Rule 2. One (and only one) output is placed in the right corner
of the rung.
Rule 3. Input devices can be connected in either series, parallel,
or combination series/parallel forms.
Rule 4. Only parallel output devices can be placed in a rung.
incorrectcorrect
Rule 5. While input devices can be represented multiple times in
the relay logic diagram, each output device can only be
represented once in the diagram.
Rule 6. All the input and output devices must be placed
horizontally.
Rule 7. Current in the relay logic diagram must flow from left to right.
Rule 8. Diagrams must be numbered and commented correctly.
Rule 9. The location of each contact associated with a coil can
be specified.
Contact and Coil I/O Programming Examples
If one input is on, nothing happens
If any two input are on, a red pilot light goes on
If any three input are on, an alarm siren sounds
If all four input are on, the fire department is notified
Instruments Mitsubishi A series
STR Store (start a new rung of a ladder
diagram)
LD Start rung with an open contact
OUT Output OUT output
AND Series components AND Series elements
OR Parallel components OR Parallel elements
NOT Inverse action (used in conjunction
with other instructions to invert
their function, e.g. ANDNOT
=NAND function.
..I As for NOT, e.g; ORI meaning
NOR function
ORB Or together parallel branches
AND And together series circuit blocks
Some typical instruction sets for Texas Instrument and
Mitsubishi are given in Table
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