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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