Programmable Logic Controller (PLC) Questions and Answers – 13

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:

Siemens S7-200 PLC

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:

Siemens S7-200 PLC Logic

Answer :

Green lamp is on, red lamp is off.

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Credits :  Tony R. Kuphaldt – under CC BY 1.0

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1 thought on “Programmable Logic Controller (PLC) Questions and Answers – 13”

  1. 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.


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