Programmable Logic Controller (PLC) Questions and Answers – 5

Suppose we have a PLC connected to three process switches as shown in this illustration:

PLC Questions - 3In the above diagram :

  • X1 to X4 : Inputs
  • Y1 to Y4 : Outputs

Determine the switch actuation statuses (i.e. low versus high process stimulus) given the “live” display of the ladder logic program shown here:

PLC Ladder Logic for Lamp


Also, determine the status of the lamp connected to the PLC’s Y1 output.

Answer :

  • Low level and low flow and low temperature.
  • The lamp will be energized.

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Credits : Tony R. Kuphaldt – under CC BY 1.0

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