A Comprehensive Guide to Photobeam Sensors for Perimeter Security

A photobeam sensor is a security device that detects the passage of people or objects using active infrared beams. Commonly installed along outdoor perimeters or building boundaries, it enables early detection of intruders and facilitates prompt response by integrating with alarm systems and surveillance cameras.

Photobeam sensors come in various models, including short-range and long-range types, as well as versions designed to operate reliably under harsh weather conditions. This allows users to select the most suitable sensor based on the specific application and site requirements.

In this article, OPTEX provides a clear and detailed explanation of how photobeam sensors work, the different types available, and how to choose the right model depending on your environment and needs.

In a typical opposing-type photobeam sensor system, the transmitter emits an infrared beam that is received by the receiver. When a person or object physically interrupts this beam, the system instantly detects the intrusion and triggers an alarm.

• Long-range detection capability (models available for up to 200 meters)
• Available in both wired and wireless versions
• Proprietary technology to minimize false alarms caused by environmental factors, small animals, and weather conditions
• Easy optical axis alignment functions for reduced installation time (SL Series)
• High-sensitivity design ensures stable detection even in extreme weather conditions such as severe cold or intense heat
• Immediate notification of reduced detection performance due to fog or rain (trouble signal output via D.Q. circuit)
• Flexible installation options for various environments (walls, fences, poles, etc.)

Photobeam sensors play a vital role in protecting premises by enabling early detection of intruders. When installed along the perimeter or boundary of a building, Photobeam sensors can detect the moment an intruder crosses the protected area and immediately trigger an alarm.

These sensors serve as a critical component in security systems, allowing for rapid detection and seamless integration with alarms and surveillance cameras to ensure immediate response.

OPTEX offers a wide range of products tailored to various applications and installation environments, and has earned the trust of customers around the world through its proven performance and reliability.

The optimal photobeam sensor varies depending on the installation site and intended purpose. Use the following criteria to help select the most suitable model for your needs.
OPTEX offers a comprehensive lineup designed to meet a wide range of environments and requirements.

• Perimeter Protection
  For monitoring large premises or boundary lines, long-range opposing-type photobeam sensors are ideal.
  OPTEX provides models with detection ranges up to 200 meters (e.g., SL-650 Series), allowing wide-area coverage with fewer units.

• Narrow Pathways and Entrances
  In areas where reliable detection is needed over short distances, mid-to-short-range models are effective.
  These sensors are also suitable for locations with limited installation space, offering flexible deployment options.

Choosing a product suited to the installation environment ensures long-term stable operation and high reliability.

• Areas with Frequent Fog or Rain
  To maintain stable detection even in low-visibility conditions, models equipped with high-sensitivity design and D.Q. circuits are highly effective.
  OPTEX’s SL-200/350/650QDM models feature A.T.P.C. (Automatic Transmitter Power Control), which automatically adjusts and optimizes the infrared beam output based on surrounding environmental conditions.
  This function helps reduce false alarms and missed detections caused by fog, frost, crosstalk, or light saturation.

• Locations with Strong Direct Sunlight or Ambient Light
  Models equipped with Sunshine Protection technology suppress false alarms caused by sunlight or reflected light.
  OPTEX’s SL-QDP and SL-QDM series use triple-layer optical filters to prevent false alarms even under intense direct sunlight, ensuring high reliability in outdoor environments.

• Regions with Frequent Lightning Strikes
  In areas prone to lightning, models with lightning-resistant design are recommended.
  Some OPTEX products include lightning protection features that reduce the risk of malfunction or damage caused by electrical surges.
  Wireless models are also effective, as they are less susceptible to lightning-related issues due to the absence of wired connections.
  ▶ Wireless models: SL-350QFR/SL-350QNR, SL-100TNR/SL-200TNR

• Locations concerned False Alarms from Birds or Falling Leaves
  Using quad-beam sensors instead of twin-beam sensors can significantly reduce false alarms caused by birds or falling leaves.
  Quad-beam sensors trigger an alarm only when all four beams are interrupted simultaneously, resulting in higher detection accuracy.

• When Installation Time Needs to Be Minimized
  Models equipped with features that support optical alignment can significantly improve installation efficiency.
  OPTEX’s SL Series includes helpful tools such as LED indicators that display alignment levels and the Sniper Viewfinder, which assists with precise optical alignment.
  In particular, the SL-200/350/650QDM models allow alignment level checks on the transmitter side, enabling one-person installation.
  • Sniper Viewfinder:
    This viewfinder features a lens with twice the magnification compared to conventional models, greatly enhancing visibility during optical alignment.
    Even in long-range installations, it enables quick and accurate setup while maintaining stable performance.

• When Want to Minimize False Alarms
  Products that incorporate quad-beam structures and Double Modulation technology help reduce false detections caused by small animals, sunlight, and ambient light interference.

• When Expanding Vertical Detection Coverage to Prevent Missed Intrusions
  In high-security areas or critical facilities, it is essential to enhance vertical surveillance to avoid blind spots and missed detections.
  By stacking multiple sensors vertically (stacking installation), the detection area can be extended upward and downward, eliminating gaps in coverage.
  OPTEX’s SL-QDP and SL-QDM series support four-channel frequency switching for infrared beams, which prevents interference between sensors during stacking installations.