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6-8

Ladder Logic (LAD) for S7-300 and S7-400

C79000-G7076-C504-02

Figure 6-3 shows a logic string of Ladder instructions that represents two

normally open contacts connected in series to a coil. The contacts are

labelled “I” for “input” and the coil is labelled “Q” for “output.” Activating a

normally open contact closes the contact. When both contacts in the logic

string are activated (that is, closed), power can flow from the power rail

across each contact to energize the coil at the end of the circuit. That is,

when both contact I 1.0 and I 1.1 are activated, power can flow to the coil.

In Diagram 1, both contacts are activated. Activating a normally open

contact closes the contact. Power can flow from the power rail across each

closed contact to energize the coil at the end of the circuit.

In Diagrams 2 and 3, because one of the two contacts is not activated, power

cannot flow all the way to the coil. The coil is not energized.

In Diagram 4, neither contact is activated. Both contacts remain open. Power

cannot flow to the coil. The coil is not energized.

I 1.0 I 1.1 Q 4.0

Diagram 1 Diagram 2

Diagram 3 Diagram 4

= activated = energized

I 1.0 I 1.1 Q 4.0

Figure 6-3 Using Normally Open Contact to Program Contacts in a Series

Programming

Contacts in Series

Configuration and Elements of Ladder Logic

1 2 ... 77 78 79 80 81 82 83 84 85 86 87 ... 317 318

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Siemens NAN 67 Series Manual de servicio Pagina 82