Introduction
Large open spaces like warehouses, gymnasiums, and open-plan offices present challenges for PIR sensors. The sheer size and often high ceilings make standard sensors ineffective.
Why Large Spaces Are Challenging
1. Limited Range
Most PIR sensors have a maximum range of 10-15 meters. In a large warehouse, this covers only a small fraction.
2. High Ceilings
Mounting sensors on high ceilings (10-20m) creates large blind spots directly below and reduces effective range.
3. Temperature Gradients
Large spaces often have temperature variations (near doors, skylights) that can cause false triggers.
4. Obstructions
Racking, machinery, and stored materials create shadows and blind spots.
Solutions
1. Multiple Sensors
The most straightforward solution: use multiple sensors with overlapping coverage. Calculate coverage areas and place sensors to eliminate blind spots.
2. Long-Range (Curtain) Lenses
Use sensors with curtain lenses designed for long distances (up to 30-40m). These have a narrow field but can cover long aisles.
3. Ceiling-Mount with Wide-Angle Lenses
For high ceilings, use sensors specifically designed for ceiling mounting with 360° coverage. These have patterns that cover a circular area below.
4. Sensor Fusion
Combine PIR with other technologies:
- Ultrasonic: Can detect motion in a wider area.
- Microwave: Longer range, penetrates some obstructions.
- Thermal arrays: Can cover large areas with people counting.
5. Zoned Detection
Divide the space into zones, each with its own sensor. This also helps identify where motion occurred.
Coverage Calculation Example
For a warehouse 50m × 30m with 10m ceilings:
- Standard PIR (10m range) would need ~15-20 sensors.
- Long-range curtain sensors (30m) along aisles could reduce this to 6-8 sensors.
Case Study: Warehouse Automation
A warehouse needed to detect personnel for safety lighting. Using 12 long-range PIR sensors with curtain lenses mounted along the ceiling, they achieved 95% coverage of the floor area. Sensors were zoned so lights turned on only in occupied zones.
Conclusion
Large spaces require careful planning and multiple sensors. Use the right lens for the application and consider combining technologies.