72 Rockwell Automation Publication 450L-UM001D-EN-P - December 2019
Chapter 6 Installation and Wiring
How to calculate the Safety Distance (S) according to EN ISO 13855 and EN
ISO 13857:
• First, calculate S use the following formula:
S = 2000 [mm/s] × T + 8 × (d – 14) [mm]
Where:
The reach/approach speed is already included in the formula.
• If the result S is ≤ 500 mm (19.6 in.), then use the determined value as the
safety distance.
• If the result S is > 500 mm (19.6 in.), then recalculate S as follows: S =
1600 × T + 8 × (d – 14) [mm]
• If the new value S is > 500 mm (19.6 in.), then use the newly determined
value as the minimum safety distance.
• If the new value S is ≤ 500 mm (19.6 in.), then use 500 mm (19.6 in.) as
the safety distance.
Example:
Stopping/run-down time of the machine = 290 ms
Response time safety-light curtain Tt < 20 ms
Response time of the control circuit = 10 [ms]
T = 290 [ms] + 20 [ms] + 10 [ms] = 320 [ms] = 0.32 [s]
Resolution of the light curtain = 14 mm (0.56 in.)
S = 2000 × 0.32 + 8 × (14 – 14) = 640 mm (25.1 in.) S > 500 mm, therefore:
S = 1600 × 0.32 + 8 × (14 – 14) = 512 mm (20.1 in.)
Figure 33 on page 71
also indicates the distance to avoid standing behind the
safety light curtain. If the light curtain is installed more than 75 mm (2.95 in.)
from the machine:
•With auto restart
• Where the dangerous area is not visible from the Reset button more
protective measures must be considered (for example, an additional
horizontal installed light curtain).
T = Stopping/run-down time of the machine [s]+ response time Tt of the
safety light curtain [s] + response time of the control circuit [s]
d = Resolution of the light curtain [mm]
S=Safety distance [mm]
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