Practice missions
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Practice missions
Mission 02 · Free PLC permissive exercise

Permission to run

Run only when every condition is right.

Make the pump run only when it is allowed. PumpOn is ON only while Start is held, Permit is ON and Fault is OFF. In every other case, PumpOn stays OFF.

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The 3D pump skid this mission runs on
Test replay

Pump runs with Start, Permit and no Fault

Test 1 of 4
Set by the testChecked by the testStep 1 of 1 · 20 ms
Level
Foundation
Time
About 8 min
Reward
+100 XP
Rig
3D pump skid
Siemens editors
SCL, LAD
Rockwell editors
Structured Text, Ladder
Course stage
2. Only run when allowed
Automatic tests

What the tests check

  1. Holding Start with Permit ON and Fault OFF runs the pump.
  2. If Permit goes OFF or Fault comes ON, the pump stops, even while running.
  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 brewery pump draws hot water from a storage tank. A low-water switch says whether there is enough to pump.

Running the pump dry can ruin its seal. Losing the water supply must stop it, even after it has started.

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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