More Safety in the Door Entry Area
The fully automatic safety light curtain "SITRANS alpha S1-Rail" from Sitron Sensor sets new standards in door monitoring for buses and trains. With up to 194 infrared beams, the system detects even the smallest objects without contact and reliably prevents accidents. TÜV-tested to EN 50126/50128/50129, SIL2-certified, and already in use on more than 150,000 vehicle doors worldwide.
Invisible Safety: Using infrared-based grid technology, the “SITRANS alpha S1-Rail” detects even the smallest objects in the door’s path. Interrupting a single light beam is enough to prevent the door from closing (Images: Sitron Sensor).
The boarding and alighting phase on buses and trains is a safety-critical moment in daily operations. Door malfunctions can lead to injuries or operational delays. The fully automatic light curtain „SITRANS alpha S1-Rail“ from Sitron Sensor delivers maximum safety and efficiency here — contactless, precise, and low-maintenance. More than 150,000 vehicle doors worldwide are now equipped with the system — a clear sign of its strong market acceptance.
High protection rating, high impact: the rugged aluminum housing (shown here in D-profile form) protects the light curtain strips even under the harshest operating conditions.
The Heart of the System
The system uses up to 194 infrared beams arranged in parallel and crossed patterns. This structure enables detection of even the smallest objects, such as dog leashes, bag straps, or children’s hands. Interrupting just a single beam immediately triggers a switching action and prevents the door from closing. The system is available in various lengths up to 2000 mm and detection heights up to 1794 mm, with a range of up to 2.5 m.
The pulsed infrared light ensures very high ambient light immunity. The parallel and crossed light beams form a fine-meshed grid. Even the smallest objects are reliably detected.
Safety and Robustness
The S1-Rail series, developed specifically for rail applications, has been tested by TÜV Nord and meets the strict EN 50126, EN 50128, and EN 50129 standards. Field data analysis based on real-world operation confirms compliance with Safety Integrity Level SIL2, meaning the system qualifies not merely as a convenience feature but as an approved safety-relevant device in rail vehicles.
In daily bus and rail operation, dirt, vandalism, mechanical stress, and changing light conditions are constant challenges. The „SITRANS alpha S1-Rail“ addresses these through:
• Dimensionally stable aluminum housings with IP54/IP67 protection – optionally up to IP69K
• Fully integrated, partially potted electronics, resistant to shock and vibration
• Pulsed infrared light that operates reliably even under strong sunlight (> 100 kLux)
These features ensure reliability — even in subway stations, under fluctuating outdoor temperatures, or in poor air quality conditions.
Easy to install and adaptable: the sensor strips can be mounted either fixed in the door frame or on the moving door leaves — ideal for both new vehicles and retrofit projects.
Maintenance-Free Thanks to AST Technology
The system features AST (Automatic Signal Tracking) functionality. This automatically compensates for misalignment and contamination — without the need for manual readjustment. Light intensity is continuously readjusted, resulting in consistently stable sensor performance — both when the vehicle is stationary and in motion. This makes the system maintenance-free in operation.
Flexible and Retrofit-Friendly
In addition to standard models, Sitron also offers custom configurations tailored specifically to vehicle type, installation space, and wiring. Retrofit projects particularly benefit from the modular design, which enables cost-efficient retrofits.
Sitron: Market Leader with a System
With the „SITRANS alpha“ series, Sitron positions itself, according to its own statements, as the market leader in safety light curtains for passenger access. The widespread use in rail and bus vehicles underscores not only the technology’s reliability but also its economic significance for modern public transit.
Conclusion: Technology That Takes Responsibility
The „SITRANS alpha S1-Rail“ impresses with technological precision, practical robustness, and certified safety. Operators get a system that protects people, reduces costs, and performs reliably — not just today, but over the long term under demanding conditions.
