Safety Light Curtain
An optical safety device forming a grid of infrared beams — breaking any beam immediately stops hazardous machine motion.
01 / Recognize it
What this sensor looks like
Learn the housing, active face, mounting, and connector before you meet it on a machine.
Hardware recognition
Know what to look for
Use the silhouette, active face, and connection style to identify the device before checking its part number and datasheet.
- Body and mounting
- Two tall narrow extrusions mount opposite each other across an access opening.
- Active face
- A vertical window contains the infrared transmitter or receiver optics.
- Cable and terminals
- Separate bottom connectors carry power, OSSD outputs, sync, and reset wiring.
02 / Understand the principle
Watch cause become a PLC signal
Follow the physical event through the sensing element and into the exact controller value.
Signal story / live loop
Safety Light Curtain: cause to controller
Now showingPhysical event
A hand enters the field → Both OSSDs drop → %I0.6–0.7 = 0
03 / Test and commission it
Commission it on the bench
Move the process, adjust the setpoint, invert the logic and inject faults. Watch the PLC value respond immediately.
Commissioning bench
Safety Light Curtain
PLC channel
%I0.6–0.7
RAW 1
Engineering value
35 %
OSSD A/B
Channel healthy
Hazard detected: both safety outputs must drop
Commissioning note: Measure stopping time and safety distance; a clear beam is not proof of a safe stop.
Field guide
A safety light curtain consists of two columns: an emitter containing a vertical array of infrared LEDs and a receiver containing a matching array of photodetectors. Beams scan across the protected area sequentially — typically thousands of times per second. If any beam is interrupted, both output signal switching devices (OSSDs) drop to 0 V within one scan cycle.
The OSSD (Output Signal Switching Device) is a dual-channel safety output — two independent transistors that drive the safety relay or safety PLC simultaneously. The safety controller verifies both channels agree; if they disagree (one stuck high), it detects a fault and requires a manual reset. This dual-channel architecture achieves Performance Level d (PLd) or Safety Integrity Level 2 (SIL2) under EN ISO 13849 and IEC 62061.
Resolution is the diameter of the smallest object the curtain will reliably detect. Finger-resolution curtains detect objects ≥ 14 mm in diameter (a finger). Hand-resolution curtains detect objects ≥ 30 mm. Body-resolution curtains (≥ 70 mm) guard larger openings where only whole-body intrusion matters.
Muting — temporarily suspending the curtain — allows material (pallets, parts) to pass through while keeping it active against personnel. Muting requires two independent muting sensors whose activation sequence and timing are verified by the safety controller.
Light curtains require commissioning by a qualified safety engineer and must be integrated with the machine's safety-rated control circuit, not standard PLC I/O.
Use this when…
- Guarding the point-of-operation on a press or stamping machine
- Creating a safe zone around a robot arm or collaborative robot
- Protecting an access opening on a packaging or assembly machine
Where you will see it
Sheet metal stamping
Light curtains on the front and sides of a power press stop the press ram instantly if an operator's hand enters the danger zone during the downstroke.
Palletiser
Finger-resolution curtains on pallet infeed openings allow pallets to pass uninterrupted while detecting any person attempting to enter the cell.
Next skill
Connect it to PLC logic
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