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Mission 19 · Pro PLC fault-finding exercise

Nuisance alarm

A valve takes a moment to open. Give it time.

Keep the check that the valve did what it was told. ValveOpen is the switch that confirms the valve is open. Raise Alarm only when it has been missing for 200 ms in a row. ValveCmd follows Start AND Permit. Feedback arriving, the command ending, or Permit going off must clear the wait and Alarm.

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

Operator report: a healthy valve travels

Test 1 of 7
Set by the testChecked by the testStep 3 of 3 · 980 ms
Level
Applied
Time
About 12 min
Reward
+200 XP
Rig
3D process tank
Siemens editors
FBD
Rockwell editors
FBD
Course stage
8. Ask for evidence
The operator’s report · process tank
Every time I start XV-101, the alarm flashes up for a second. The valve opens fine and the alarm clears itself. If the valve really does stick, the alarm stays on, which is right.
Automatic tests

What the tests check

  1. A healthy valve opening does not raise the alarm.
  2. Feedback missing for 200 ms in a row raises the alarm, never earlier.
  3. Ending the request, or feedback arriving, restarts the 200 ms wait.
  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 drinks operator gets an alarm whenever the ingredient valve starts to open. The valve then opens fully and the alarm clears.

Too many false alarms teach people to ignore alarms. Removing the alarm completely would hide a valve that really sticks.

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.

Keep going

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