Beginner 04 — Stop button (NC contact)
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Briefing
The light is on by default. Pressing STOP_BUTTON should turn it OFF. That's a normally-closed (NC) contact — current passes through it until the input is true, then it breaks. Here “NC” describes the ladder instruction: it is true when its tag is false. The simulator uses an active-high button tag (FALSE released, TRUE pressed). Do not infer physical E-stop wiring from this model; real safety functions use de-energise-to-trip field circuits, monitored safety equipment, and validation.
Objectives
- When STOP_BUTTON is false (released), LIGHT is on
- When STOP_BUTTON is true (pressed), LIGHT is off
Hints
- Use a normally-closed contact, not a normally-open one.
- In IEC, the slash prefix marks an NC contact: | /STOP_BUTTON |.
I/O Table
Inputs
STOP_BUTTONSimulated stop command (TRUE when pressed)
BOOL · %I0.0
Outputs
LIGHTIndicator lamp
BOOL · %Q0.0
Your program will be tested against:
All test cases run automatically when you submit. Assertions are hidden until you pass.
- #1STOP released → LIGHT on
NC contact lets current through when input is false
- #2STOP pressed → LIGHT off
NC contact breaks the rung when input goes true
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