Practice missions
Practise in
0 XP
Practice missions
Mission 04 · Free ladder logic exercise

Make it stay running

Press Start once. It runs until Stop.

Press Start once and the pump keeps running after you let go. This needs a , where PumpOn remembers it was started. Pressing Stop or losing Permit turns PumpOn OFF. Stop always wins, even with Start held.

Free, with no sign-up. Create a free account to keep your progress on every computer.

The 3D pump skid this mission runs on
Test replay

Pump keeps running after a short Start press

Test 1 of 6
Set by the testChecked by the testStep 2 of 2 · 120 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
3. Remember a Start request
Automatic tests

What the tests check

  1. A short press of Start keeps PumpOn ON after you let go.
  2. Stop turns PumpOn OFF, even while Start is held.
  3. Turning Permit OFF stops the pump. With Start released, turning Permit back ON does not restart it.
  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

In a building's pump room, an operator presses Start once and walks away. The pump should keep running until someone presses Stop.

Without a seal-in, where the pump remembers it was started, it stops as soon as Start is let go. If that memory ignores Stop, water keeps pumping.

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

Next in the course