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Practice missions
Mission 27 · Pro PLC fault-finding exercise

Complete, but still pumping

Find the command that stays on after its step ends.

Add the missing end-of-cycle action. Start begins recirculation, and the pump keeps running after the chart leaves the starting step. Stop finishes the cycle and turns PumpOn off. Reset goes back to Ready with PumpOn and Done off.

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The 3D pump skid this mission runs on Pro mission
Test replay

Operator report: Complete with pump still on

Test 1 of 5
Set by the testChecked by the testStep 5 of 5 · 500 ms
Level
Applied
Time
About 12 min
Reward
+200 XP
Rig
3D pump skid
Siemens editors
GRAPH
Rockwell editors
SFC
Course stage
14. Give commands an end
The operator’s report · pump skid
I pressed Stop and the recirculation chart went to Complete. Done is on, but P-101 is still turning. The only thing that stops it is resetting the whole chart.
Automatic tests

What the tests check

  1. The pump stays on in the Recirculating step.
  2. Within two of Stop, Done is on and PumpOn is off.
  3. The pump stays off once the cycle is complete. Reset clears both .
  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 blending operator sees Batch complete, but the transfer pump is still running. The sequence has already left the step that started it.

A stored command stays on after its step ends. The pump keeps moving liquid until another instruction clears it.

Where you'd find thisWater for the top floors

In a block of flats, a basement tank holds water from the mains. Two pumps push it up to the taps above. One runs while the other waits as a spare. A low-water switch stops the pumps before the tank runs dry.

  1. Street mainsWater enters the building
  2. Storage tankHolds a supply for the pumps
  3. Water pumpsPush water to the floors aboveYou are here
  4. Taps upstairsResidents use the water they need
On a real site: places, parts and safety
  • Block of flats — pushing water up to the top floors
  • Brewery — sending hot water to a brewing tank
  • Water-treatment works — moving water between filter tanks
  • Office building — pumping water round the heating pipes

A low-water switch can take away permission to run. The pump must stop before it runs dry and damages its seal.

The PLC can say ON even when a pump has failed. Check the measured flow as well as the command.

The Stop input in these exercises is not an emergency stop. Real machines also need guards, emergency stops and a safe way to cut the power.

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

Keep going

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