Notes:
1. The OSHA-recommended hand speed constant
K
has been determined by various studies and, although
these studies indicate speeds of 1600 mm/sec. (63 in/sec.) to more than 2500 mm/sec. (100 in/sec.), they
are not conclusive determinations. Consider all factors, including the physical ability of the operator, when
determining the value of
K
to be used.
2. The recommended hand speed constant
K
, derived from data on approach speeds of the body or parts of
the body as stated in ISO 13855.
3.
T
s
is usually measured by a stop-time measuring device. If the machine manufacturer's specified stop time is
used, at least 20% should be added to allow for possible clutch/ brake system deterioration. This
measurement must take into account the slower of the two MPCE channels, and the response time of all
devices or controls that react to stop the machine.
WARNING:
•
Stop time (Ts) must include the response time of all devices or controls that react to stop
the machine
•
If all devices are not included, the calculated safety distance (Ds or S) will be too short, which can
lead to serious injury or death.
•
Include the stop time of all relevant devices and controls in your calculations.
•
If required, each of the two machine primary control elements (MPCE1 and MPCE2) must be
capable of immediately stopping the dangerous machine motion, regardless of the state of the
other. These two channels of machine control need not be identical, but the stop time performance
of the machine (Ts, used to calculate the safety distance) must take into account the slower of the
two channels.
5.2.2 Examples
U.S. Applications, Model S4BR30-600-S
K
= 63 inches per second (the hand speed constant set by OSHA)
T
s
= 0.31 (0.250 second is specified by the machine manufacturer; plus 20% safety factor; plus 13 ms for XS26-2
Safety Controller response time)
T
r
= 0.010 seconds (the specified response time of a S4BR30-600-S System)
D
pf
= 3.1 inches (30 mm resolution)
Substitute the numbers into the formula as follows:
D
s
= K × ( T
s
+ T
r
) + D
pf
D
s
= 63 × (0.31 + 0.010) + 3.1 = 23.3 in
Mount the S4B emitter and receiver so that no part of the defined area will be closer than 23.3 inches to the closest
reachable hazard point on the guarded machine.
European Applications, Model S4BR30-600-S
K
= 1600 mm per second
T
= 0.32 (0.250 second specified by machine manufacturer; plus 20% safety factor; plus 13 ms XS26-2 Safety
Controller response time), plus 0.010 seconds (the specified response time of a S4BR30-600-S System)
C
= 8 × (30 – 14) = 128 mm (30 mm resolution)
Substitute the numbers into the formula as follows:
S = (K × T ) + C
S = (1600 × 0.32) + 128 = 640 mm
Mount the S4B emitter and receiver so that no part of the defined area will be closer than 640 mm to the closest reachable
hazard point on the guarded machine.
S4B Safety Light Curtain
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