Practice missions
Practise in
0 XP
Practice missions
Mission 16 · Pro analogue level control exercise

Stop the short cycling

Two switch points. A calmer pump.

Turn PumpOn ON when Level falls below 30%. Keep filling past 30%, and stop at 70%. Then stay OFF until Level drops below 30% again. This stops short cycling, where the pump flicks on and off and wears out. PumpOn runs only while Permit is ON; losing Permit stops it at once.

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

Fills from below 30% up to 70%, then waits

Test 1 of 4
Set by the testChecked by the testStep 5 of 5 · 100 ms
Level
Applied
Time
About 12 min
Reward
+200 XP
Rig
3D process tank
Siemens editors
FBD
Rockwell editors
FBD
Course stage
7. Keep control steady
Automatic tests

What the tests check

  1. Level below 30% turns PumpOn ON.
  2. Rising past 30% does not stop it.
  3. At 70% PumpOn turns OFF and stays OFF until Level is below 30% again.
  4. Turning Permit OFF stops PumpOn at once, even mid-fill.
  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 building storage tank fills when its level is low. The pump should keep going until the tank reaches the upper limit.

Starting and stopping around one level wears out the motor and pump. Two limits, one to start and one to stop, let each fill finish.

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

Next in the course