Version 10.12.2019
page 10
WERAC Elektronik GmbH
Note: When using an access protection with two to four single beams the entry of a body or
body parts can not be detected absolutely.
Note: Multibeam light barriers are possible with other light barrier distances (e.g. 100 mm
resolution) for access protection by means of horizontally arranged light grids (see ISO 13855
Section), provided that they are permitted in type C standards of machines.
6.4
Height of guarded area
The height of guarded area SH is indicated on each product label and in the selection tables.
The guarded area stretches slightly beyond the ends of the light grid modules.
6.5
Response time of the light grids
The response time t
R
results from a basic time t
RG
(relay release time and self-checking) of
16 ms and a time t
RL
which is dependent on the number of lines = 0.16 ms per line.
When using a single, non-cascaded light grid the valid response time can be found on the
product label on the emitters and receivers.
In the case of cascades, the response time is dependent on the total number of lines in all light
grids. The following applies: t
R cascade
= t
RG
+ t
RL (total)
It is not valid to add the response times that are given on the product label. It is necessary to
use the above-quoted formula.
Example: Two light grids with 30 lines and 48 lines are required for the protection of an
automatic warehouse system. The response time is calculated as follows:
t
R cascade
= t
RG
+ t
RL(total)
= 16 ms + (30 + 48) · 0.16 ms = 16 ms + 12.48 ms = 28.5 ms
SH = Height of guarded area
N
= Number of lines
A
= Resolution (14, 30 or 40 mm)
LD
= Light beam diameter
4 mm at 14 mm resolution,
5 mm at 30 and 40 mm resolution
SH = (N + 1) x (A - LD) + LD
For a light grid with 14 mm resolution:
SH = (N + 1) x (14 - 4) mm + 4 mm
= (N + 1) x 11 mm + 4 mm
For a light grid with 30 mm resolution:
SH = (N + 1) x (30 - 5) mm + 5 mm
= (N + 1) x 25 mm + 5 mm
For a light grid with 40 mm resolution:
SH = (N + 1) x (40 - 5) mm + 5 mm
= (N + 1) x 35 mm + 5 mm
Fig. 7:
Beam geometry for
resolution 14, 30 and 40 mm
H
e
ig
h
t o
f
g
ua
rd
e
d
a
re
a
30 mm
5 mm
25 mm
30 mm
H
e
ig
h
t o
f
g
ua
rd
e
d
a
re
a
14 mm
4 mm
10 mm
14 mm
10 mm
40 mm
40 mm
H
e
ig
h
t o
f
g
ua
rd
e
d
a
re
a
35 mm
5 mm
