Calculation of the minimum distance according to ISO 13855
T
he calculation of the minimum distance is based on international or national stan‐
dards and statutory requirements applicable at the place of installation of the machine.
If the minimum distance is calculated according to ISO 13855, then it depends on the
following points:
•
Machine stopping time (time interval between triggering the sensor function and
the end of the machine’s dangerous state)
•
Response time of the protective device
•
Reach or approach speed of the person
•
Resolution (detection capability) of the safety light curtain
•
Type of approach: orthogonal (at right angles) or parallel
•
Parameters specified based on the application
For the USA (scope of OSHA and ANSI), different regulations may apply, e.g.:
a) Laws: Code of Federal Regulations, Title 29 (CFR 29), Part 1910.217
b) Standards: ANSI B11.19
Complementary information
Mor
e information is available in the ISO 13855 standard and in the Guide for Safe
Machinery.
SICK offers a stopping/run-down time measurement service in many countries.
Further topics
•
"R
esponse time", page 56
4.3.2.1 Calculating minimum distance from the hazardous point
Important information
DANGER
Minimum dis
tance from the hazardous point is too small
The dangerous state of the machine may not be stopped or not be stopped in a timely
manner due to a minimum distance that is too small.
b
Calculate the minimum distances for the machine in which the safety light curtain
is integrated.
b
When mounting the safety light curtain, observe the minimum distance.
Approach
The example shows the calculation of the minimum distance in accordance with ISO
13855 for an orthogonal (right-angled) approach to the protective field. A different cal‐
culation may be required depending on the application and the ambient conditions
(e.g., for a protective field parallel to or at any angle to the direction of approach or an
indirect approach).
1. First, calculate S using the following formula:
S = 2,000 mm/s × T + 8 ×(d – 14 mm)
Where:
°
S = minimum dis
tance in millimeters (mm)
°
T = machine stopping time + response time of the protective device after
interruption in the light path in seconds (s)
°
d = resolution of the safety light curtain in millimeters (mm)
The reach or approach speed is already included in the formula.
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