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Rockwell Automation Publication 440L-IN012A-EN-P - November 2017
GuardShield Type 4 and GuardShield Remote Teach
Response Time
The response time of the GuardShield safety light curtain depends on
the height of the protective field, the resolution, and the coding of the
system.
The response time of a cascading system is the response time of the
interrupted individual segment-pair response time.
Table 9 - Response Time for Finger Resolution (14 mm) [mm (in.)]
Table 10 - Response Time for Hand Resolution (30 mm) [mm (in.)]
Determine the Safety Distance
The light curtain must be mounted with proper safety distance
• From the point of danger
• From reflective surfaces
US Safety Distance Formula
This distance, referred to as the safety distance, must be properly
calculated before determining the safety light-curtain protective-height
and mounting the light curtains on the machine. Failure to calculate this
safety distance accurately results in operator injury.
In the United States, there are two formulas that are used to calculate
the safety distance. The first, the OSHA formula, is the minimum
requirement for the calculation of the safety distance. The second
formula, the one we recommend, is the ANSI formula, which
incorporates additional factors to be considered when calculating the
safety distance.
OSHA Safety Distance Calculation Formula
The OSHA safety distance formula as specified in CFR Subpart O
1910.217 is as follows:
D
s
= 63 X T
D
s
Safety Distance
63
Is the OSHA recommended hand speed constant in inches
per second
T
Is the total stop time of all devices in the safety circuit, which
is measured in seconds. This value must include all
components that are involved to stop the hazardous motion
of the machinery. For a mechanical power press, it is the stop
time that is measured at approximately the 90º position of the
crankshaft rotation.
Resolution
Protective
Height
Number of
Beams
Response Time
w/o Coding
Response Time
w/Coding
14 (0.55)
160 (6.3)
16
20 ms
30 ms
14 (0.55)
320 (12.5)
32
20 ms
30 ms
14 (0.55)
480 (18.8)
48
20 ms
30 ms
14 (0.55)
640 (25.1)
64
20 ms
30 ms
14 (0.55)
800 (31.4)
80
20 ms
30 ms
14 (0.55)
960 (37.7)
96
20 ms
30 ms
14 (0.55)
1120 (44.0)
112
20 ms
30 ms
14 (0.55)
1280 (50.3)
128
20 ms
30 ms
14 (0.55)
1440 (56.6)
144
20 ms
30 ms
14 (0.55)
1600 (62.9)
160
25 ms
35 ms
14 (0.55)
1760 (69.2)
176
25 ms
35 ms
Resolution
Protective
Height
Number of
Beams
Response Time
w/o Coding
Response Time
w/Coding
30 (1.18)
160 (6.3)
8
20 ms
30 ms
30 (1.18)
320 (12.5)
16
20 ms
30 ms
30 (1.18)
480 (18.8)
24
20 ms
30 ms
30 (1.18)
640 (25.1)
32
20 ms
30 ms
30 (1.18)
800 (31.4)
40
20 ms
30 ms
30 (1.18)
960 (37.7)
48
20 ms
30 ms
30 (1.18)
1120 (44.0)
56
20 ms
30 ms
30 (1.18)
1280 (50.3)
64
20 ms
30 ms
30 (1.18)
1440 (56.6)
72
20 ms
30 ms
30 (1.18)
1600 (62.9)
80
20 ms
30 ms
30 (1.18)
1760 (69.2)
88
20 ms
30 ms
IMPORTANT
Determining Stop Time: The measurement of stopping time
(T
s
) must include the stopping times of all devices in the stop
circuit. Not including all device and control system elements
when calculating T
s
results in an inaccurate safety distance
calculation.
ATTENTION:
The GuardShield Type 4 safety light curtains must be
mounted at a sufficient distance from the pinch point or point of
operation hazard. A sufficient distance helps confirm that the
machine stops before a finger, hand, arm, or body reaches the hazard.
IMPORTANT
According to EN ISO 13855, regardless of the calculated safety
distance, never mount GuardShield Type 4 safety light curtains
closer than 100 mm (4 in.) from the point of operation or pinch
point hazard.
IMPORTANT
The T number must include the response times of all
devices,
including:
• Response time of the safety light curtain
• Safety light curtain controller (if used)
• Control circuit of the machine, and
• Any other devices that react to stop the hazardous motion
of the machinery.
