Machine Safety
Light Curtain / AOPD Safe Distance (ISO 13855)
Calculate the minimum safe distance for installing an Active Opto-electronic Protective Device (AOPD), such as a light curtain or safety laser scanner.
Units:
The hand speed constant K = 2000 mm/s is the minimum per ISO 13855. Some standards specify 1600 mm/s. Always use 2000 mm/s unless your risk assessment justifies a lower value. Never install a light curtain within the calculated minimum distance.
Ds = K × (T_s + T_r + T_c) + C | C = 8 × (d − 14) [detection zone addition]
Input
Machine stopping time T_s iTime for the machine to reach a safe state after the safety signal is issued, in milliseconds. Measure with a stop-time measurement device.
ms
AOPD response time T_r iResponse time of the light curtain/AOPD from detection to output signal, in milliseconds. From manufacturer datasheet.
ms
AOPD resolution d iMinimum detectable object diameter of the AOPD in mm. Finger detection: 14–20mm. Hand detection: 30–40mm. Body detection: >70mm.
mm
Hand speed constant K iApproach speed of the human body. ISO 13855 minimum: 2000 mm/s. Use 2000 mm/s for industrial machinery.
mm/s
Result
Total reaction time T_s + T_r [ms]
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Detection zone addition C [mm]
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Minimum safe distance Ds [mm]
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Design distance (rounded up) [mm]
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Detection capability
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