10.4 LADDER DIAGRAMS

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These diagrams are read from left to right, top to bottom.

For the ladder logic below the sequence of operations would be B1, B2 on the top first, then the bottom. This would be followed by T1, then F1.

Power flow can be used to consider how ladder diagrams work. Power must be able to flow from the left to the right.

10.4.1 Ladder Logic Design

eg. Burglar Alarm

1. If alarm is on, check sensors.

2. If window/door sensor is broken (turns off), sound alarm and turn on lights.

3. If motion sensor goes on (detects thief), sound alarm and turn on lights.

A = Alarm and lights switch (1 = on)

W = Window/Door sensor (1 = OK)

M = Motion Sensor (0 = OK)

S = Alarm Active switch (1 = on)

10.4.2 A More Complicated Example of Design