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Practice missions
Mission 41 · Pro PLC fault-finding exercise

It started on its own

After a drive reset the pump restarted. Find the memory that survived the trip.

Find why P-101 restarts by itself after a fault reset, and fix it. A trip must turn DriveRun OFF and cancel the run request. After a reset, the pump stays OFF until someone presses Start. Keep the rest: Stop wins, FaultLamp shows DriveFault, and DriveReset follows FaultReset only while DriveRun is OFF.

This mission is part of ProTry the full course, every mission and the expert challenges free for 7 days. No card needed.
The 3D pump skid this mission runs on Pro mission
Test replay

Operator report: restart after a reset

Test 1 of 5
Set by the testChecked by the testStep 12 of 12 · 2.7 s
Level
Advanced
Time
About 15 min
Reward
+250 XP
Rig
3D pump skid
Siemens editors
SCL, LAD, FBD, GRAPH
Rockwell editors
Structured Text, Ladder, FBD, SFC
Course stage
25. Trip, reset, restart on purpose
The operator’s report · pump skid
P-101’s drive tripped on overload. The fitter cleared the blockage, switched the overload off and pressed Fault reset. The pump started straight back up. Nobody pressed Start, and the fitter’s hand was still near the coupling.
Automatic tests

What the tests check

  1. After a trip and a reset, DriveRun stays OFF until a new Start.
  2. A trip still turns DriveRun OFF at once.
  3. Start, Stop, FaultLamp and DriveReset still work as before.
  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

After a drive trip and reset, a pump started again with nobody pressing Start. The fitter was still beside it.

Old run memory survived the trip. Finding and removing it stops a surprise restart, one of the classic causes of injury.

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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