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Mission 21 · Pro PLC alarm handling exercise

Acknowledge, then reset an alarm

Treat the high level, the alarm and the horn as three separate things.

If Level stays above 90% for two seconds, Alarm and Horn on. Latched means they stay on by themselves. Ack silences the Horn only. Alarm stays on until Reset is pressed with Level at or below 90%. A new alarm after Reset must sound the Horn again.

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The 3D process tank this mission runs on Pro mission
Test replay

The exact two-second boundary

Test 1 of 7
Set by the testChecked by the testStep 4 of 4 · 2.3 s
Level
Applied
Time
About 20 min
Reward
+250 XP
Rig
3D process tank
Siemens editors
SCL, LAD
Rockwell editors
Structured Text, Ladder
Course stage
10. Acknowledge is not reset
Automatic tests

What the tests check

  1. Level must stay high for 2 s without a break. One at a normal level restarts the wait.
  2. Ack never clears Alarm. Reset does nothing while Level is still high.
  3. Alarm and Horn stay on until someone deals with them. A new alarm sounds the Horn again.
  1. Try it Use the buttons below the model and watch the rig respond.
  2. Test solution Every check runs on your code in one press.
  3. Replay If one fails, step through it one scan at a time to see why.
Why it matters

Where you’d see this on site

A tank in the mixing room fills too high and a horn sounds. The operator presses Ack to silence it while checking the inlet valve.

Silencing the horn must not clear the high-level alarm. If the level goes too high again later, the horn must sound again.

Where you'd find thisMaking one batch of drink

At a drinks factory, valves let measured amounts of water and syrup into a mixing tank. An electric mixer blends them into one batch. An outlet valve then sends the drink to a holding tank. Filling machines bottle it from there.

  1. Ingredient tanksHold the water and syrup
  2. Mixing tankFill, mix and measure one batchYou are here
  3. Holding tankKeeps the finished drink ready
  4. Bottle fillerPuts the drink into bottles
On a real site: places, parts and safety
  • Drinks factory — blending water and syrup
  • Paint factory — mixing ingredients into a consistent colour
  • Water-treatment works — preparing a measured chemical mixture
  • Brewery — heating water for washing equipment

A full tank does not close its own inlet. Water keeps arriving until the valve closes, so an open inlet can flood the room.

A heater that is not covered by liquid can overheat. Real tanks have separate safety devices as well as the PLC programme.

The sizes, timings and cutaways are teaching choices, not a drawing of any one real installation.

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