Programmable Logic Controller (PLC) Questions and Answers – 3

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

PLC Programming Questions

In 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:

Switch ladder logic program

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

Answer :

  • High pressure and low flow and high temperature.
  • The lamp will be de-energized.

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Credits :  Tony R. Kuphaldt – under CC BY 1.0

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