Practice missions
Practise in
0 XP
Practice missions
Mission 65 · Pro PLC programming exercise

Both hands, checked twice

Add checked palm buttons, an emergency stop and a reset to the two-hand press.

Keep every two-hand rule from “Both hands, every time”, read both contacts of each palm button and lock the press out if a pair stops making sense. Add an emergency stop that needs a Reset.

Training only. This is not a certified safety system. On a real machine these rules run in a safety relay or a safety PLC, designed and validated to ISO 13849-1 or IEC 62061.

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

Reset, then two hands

Test 1 of 5
Set by the testChecked by the testStep 12 of 12 · 940 ms
Level
Advanced
Time
About 45 min
Reward
+500 XP
Rig
3D two-hand control press
Siemens editors
Ladder (LAD), SCL
Rockwell editors
Ladder, Structured Text
Beckhoff editors
Structured Text
Course stage
33. Safety lab 2: trust nothing single
Automatic tests

What the tests check

  1. A button with one contact stuck never counts as pressed.
  2. Contacts that agree for 0.2 s a fault: FaultLamp ON and the ram returns.
  3. The E-stop sets RamDown OFF at once and needs a fresh Reset.
  4. Reset needs the E-stop out and both buttons properly released.
  5. The “Both hands, every time” rules still hold: together, held, guard shut, released between strokes.
  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

Two-hand stations use buttons with a normally open and a normally closed contact. The safety relay checks each pair, as EN ISO 13851 describes.

A button whose contact welds shut looks pressed for ever. The release rule would then never be met, or worse, the press could stroke with one hand. Reading both contacts catches it at once.

Where you'd find thisKeep both hands on the buttons, and out of the tools

Presses are among the most dangerous machines in any factory. Two-hand control keeps the operator's hands on the console while the tools close, and an interlocked guard stops anyone reaching in.

  1. LoadGuard open, blank in
  2. Close guardInterlock made
  3. Two handsStroke downYou are here
  4. UnloadDrawn cup out
On a real site: places, parts and safety
  • Metal pressing and deep drawing
  • Riveting, staking and crimping stations
  • Assembly presses in electronics and automotive

In real machines these rules are enforced by safety relays or a safety PLC, so a programming mistake cannot defeat them. Here you write them to understand why they exist.

Tying one button down to run with one hand is the classic way operators are hurt: that is why both must be released before the next stroke.

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

Keep going

Next in the course