DEVICE TYPES, PL/CAT REQUIREMENTS, AND INSTALLATION (Q&A)

Light Curtains (Optoelectronic Safety Grids):
Used for finger, hand, or body detection based on resolution:

• 14 mm – finger detection
   
• 30 mm – hand detection
   
• 70–90 mm – body access
  Common at conveyor openings, robotic cell entry points, and manual load stations.
   

Safety Multi-Beam / Access Curtains:
2–4 beam systems for body detection at perimeter openings or materials flow points.

Safety Laser Scanners:
Used where presence detection must cover a floor area or zone.
Essential for:

• AMRs/AGVs
   
• Pallet stations
   
• Perimeter protection where fixed guarding isn’t feasible
   

Pressure Mats / Edge Devices:
Used as secondary protective measures or for large perimeter zones.

Performance Level (PL) – Reliability Rating (a–e):
A measure of how reliably the safety function prevents dangerous failure.

• PL a/b: Low-risk applications
   
• PL c: Moderate
   
• PL d/e: High-risk applications (most robotics and automated lines fall here)
   

Safety Category (CAT 1–4):
Describes the architecture and fault tolerance of the circuit:

• CAT 1: Basic circuitry
   
• CAT 2: Periodic testing, limited fault detection
   
• CAT 3: Single-fault tolerance with diagnostics
   
• CAT 4: Highest fault tolerance and diagnostic coverage
   

Most robotic/automated systems require CAT 3 or CAT 4 to achieve PL d or PL e.

1. Safety Distance Calculation (Mandatory)
The device must be placed far enough from the hazard to allow the machine to stop before contact.

This requires:

• Human approach speed
   
• Full machine stop time (not just the curtain’s response time)
   
• Intrusion depth based on resolution
   

If the device is too close, the operator can reach the hazard before the machine stops.

2. Correct Mounting Height and Orientation

• Avoid reach-over, reach-under, and reach-around conditions
   
• Ensure vertical alignment and stability
   
• Maintain proper separation from reflective surfaces
   
• Use correct height for the protection objective (finger, hand, or body)
   

3. Safety-Rated Wiring Architecture

Light curtains must connect to:

• A safety relay, or
   
• A safety PLC with the required CAT/PL rating
   

Never to standard control I/O.

4. Stop-Time Measurement and Validation
A physical test using a calibrated stop-time meter is required to confirm the machine stops fast enough to meet the safety distance.

5. Functional Testing and Documentation
Testing includes:

• Beam alignment
   
• Muting logic
   
• Blanking
   
• Perimeter reflection checks
   
• Device response
  Followed by documentation of:
   
• PL validation
   
• CAT architecture
   
• Calculations and RA
   
• Routine test schedules
   

Muting:
Allows material (like pallets) to pass without stopping the machine.
Must use safety-rated logic and can never permit a person to bypass protection.

Static or Floating Blanking:
Permits fixed obstructions but must be engineered so the blanked beams cannot be used as a path to reach the hazard.

Mirrors:
Used to extend coverage around corners but must account for signal loss, alignment, and reflection angles.
 

Industrial & Collaborative Robots:

Light curtains guard access points to industrial cells.
Cobots may require light curtains or scanners depending on force/speed monitoring and task layout.

AMRs/AGVs:

Use safety laser scanners for dynamic zones, but fixed load/unload stations often rely on light curtains or multi-beam devices to detect human presence at transfer points.
 

• Risk assessment identifying required PL
   
• Light curtain selection justification
   
• Safety distance calculations
   
• Stop-time test results
   
• CAT/PL validation documents
   
• Wiring diagrams
   
• Routine inspection and test records
   
• Maintenance and failure logs