Practice missions
Practise in
0 XP
Practice missions
Mission 13 · Free PLC fault-finding exercise

It never reaches three

Something keeps clearing the count. Find it.

Count three separate bottles arriving at BottlePresent, one for each OFF-to-ON change. Then turn Done ON and ConveyorOn OFF. A bottle sitting on the counts once. Only the Reset may clear the count and start a new group of three.

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

The 3D filling line this mission runs on
Test replay

Operator report: three arrivals, no completion

Test 1 of 5
Set by the testChecked by the testStep 6 of 6 · 800 ms
Level
Applied
Time
About 12 min
Reward
+200 XP
Rig
3D filling line
Siemens editors
SCL, LAD
Rockwell editors
Structured Text, Ladder
Course stage
5. Count an event once
The operator’s report · filling line
Three bottles went past PE-101 and the conveyor just kept going. Done never came on. I watched the count: every time a bottle sits on the sensor, it drops back to zero. Nobody touched Reset.
Automatic tests

What the tests check

  1. A bottle that sits on the sensor counts once.
  2. The third bottle to arrive stops the conveyor.
  3. Reset clears Done and starts a fresh group of three.
  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 packing operator watches bottles pass the sensor, but the count never reaches three. It seems to drop back after each bottle.

A reset in the wrong place wipes out real bottles. The batch never completes, so finished bottles wait on the line.

Where you'd find thisPutting drinks into bottles

At a soft-drinks factory, empty bottles arrive on a moving belt. A sensor tells the controller when a bottle is under the filling nozzle. The valve opens, fills the bottle, then closes before the belt moves again. Caps and labels go on before the bottles are packed.

  1. Empty bottlesThe belt brings them to the nozzle
  2. Fill each bottleStop it, fill it, then let it moveYou are here
  3. Add caps and labelsSeal the drink and name the product
  4. Pack the bottlesPut finished bottles into boxes
On a real site: places, parts and safety
  • Soft-drinks factory — filling bottles without spills
  • Dairy — putting milk into bottles
  • Cleaning-products factory — measuring liquid into containers
  • Food packaging line — counting bottles before packing

If the filling valve opens without a bottle under it, liquid spills onto the belt. If the line jams, the valve must not keep filling.

Real conveyors need guards. The power must be safely locked off before anyone clears a blockage. The Stop input here is not an emergency stop.

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

Keep going

Next in the course