Siemens NAN 67 Series Manual de Serviço descarregar pdf (Página 84)

6-10

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

C79000-G7076-C504-02

Figure 6-4 shows a logic string of Ladder instructions that represent two

normally open contacts connected in parallel 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 either one contact in the

logic string (I 1.1) or the other contact in the logic string (I 1.0) is activated

(that is, closed), power can flow from the power rail to energize the coil

(Q 4.0) at the end of the circuit. If both contacts in the logic string are

activated, power can flow from the power rail to energize the coil.

In Diagrams 1 and 2, one contact is activated and the other is not. Activating

a normally open contact closes the contact. Power can flow from the power

rail across the closed contact and continue to the coil at the end of the circuit.

Because the two contacts are connected in parallel, only one of the two

contacts need be closed for the power flow to continue to the coil at the end

of the circuit to energize the coil.

In Diagram 3, both contacts are activated, enabling the power to flow across

the two closed contacts to the end of the circuit to energize the coil.

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

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

I 1.1

Diagram 1 Diagram 2

Diagram 3 Diagram 4

= activated = energized

I 1.0 Q 4.0

I 1.1

Q 4.0

I 1.0

Q 4.0

I 1.1

I 1.0

Q 4.0

I 1.0

Figure 6-4 Using Normally Open Contact to Program Contacts in Parallel

Programming

Contacts in

Parallel

Configuration and Elements of Ladder Logic

1 2 ... 79 80 81 82 83 84 85 86 87 88 89 ... 317 318

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