Siemens S7-200 PLC Questions and Answers
Suppose we have a Siemens S7-200 PLC connected to a pair of process switches and light bulbs as shown in this illustration:
Examine the following relay ladder logic (RLL) program for this Siemens PLC, determining the statuses of the two lamps provided the pressure switch sees a fluid pressure of 30 PSI and the level switch sees a liquid level of 4 feet:
Answer :
Green lamp is on, red lamp is off.
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In the Relay Ladder Logic program, you have to show the second line L2 of the power supply, or else both lamps will be off whatever the status of the inputs.