PLC exercise – Tank level monitoring

Work order: Tank level monitoring

The filling level of a container in a chemical plant is to be checked by means of 3 capacitive sensors. A PLC evaluates these signals and indicates the result by the signal lights H1 to H3, as shown in the technology diagram below.

Tank level monitoring

fig.: Tank level monitoring

When the system is in operation, the sensor signals are to be evaluated as follows:

  • If the filling level is correct, sensors B1 and B2 respond.
  • As soon as sensor B3 responds, overflow should be indicated.
  • A fill level that is too small is indicated as soon as B1 responds, but B2 not.
  • The tank is considered empty when the sensor B1 delivers a 0-signal.

In case a signal status which does not make sense due to a faulty sensor, the signal light H4 indicates an error. The case that all three sensors do not deliver a signal is not regarded as an error. For a better understanding, the signal states of the sensors and the signal lights are compiled in the following figure. Possible malfunctions are not shown!

Tank level monitoring - sensor signals and signal lights

fig.: Tank level monitoring - sensor signals and signal lights

Work steps:

  • Value table for the signal lights H1 to H4. You may specify a value table with 4 output columns.   (4 Points)
  • Logic equation for H1 to H4.   (4 Points)
  • Give the logic diagram.   (4Points)

=>  Get the solution