Banner EZ-SCREEN Instruction manual - page 12
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. Ts 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: Determine Correct Stop Time
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. This
can lead to serious bodily injury or death. Be sure to 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.
Examples
Example: U.S. Applications, Model
K
= 63 in. per second (the hand speed constant set by OSHA)
Ts
= 0.32 (0.250 second is specified by the machine
manufacturer; plus 20% safety factor; plus 20 ms for
interface module IM-T-9A response time)
Tr
= 0.0105 seconds (the specified response time of an
SLPP14-270 EZ-SCREEN LP)
Dpf
= 0.94 in (14 mm resolution)
Substitute the numbers into the formula as follows:
Ds = K × ( Ts + Tr ) + Dpf
Mount the EZ-SCREEN LP emitter and receiver so that no part of the
defined area will be closer than 21.8 inches to the closest reachable hazard
point on the guarded machine.
Example: European Applications, Model
K
= 1600 mm per second
T
= 0.33 (0.250 second specified by machine manufacturer;
plus 20% safety factor; plus 20 ms interface module
response time), plus 0.0105 seconds (the specified
SLPP14-270 response time)
C
= 8 × (14 – 14) = 0 mm (14 mm resolution)
Substitute the numbers into the formula as follows:
S = (K × T ) + C
Mount the EZ-SCREEN LP emitter and receiver so that no part of the
defined area will be closer than 528 mm to the closest reachable
hazard point on the guarded machine.
3.1.2 Reducing or Eliminating Pass-Through Hazards
A pass-through hazard is associated with applications where personnel may pass through a safeguard (which issues a stop
command to remove the hazard), and then continues into the guarded area, such as in perimeter guarding. Subsequently,
their presence is no longer detected, and the related danger becomes the unexpected start or restart of the machine while
personnel are within the guarded area.
In the use of light screens, a pass-through hazard typically results from large safety distances calculated from long
stopping times, large minimum object sensitivities, reach-over, reach-through, or other installation considerations. A pass-
through hazard can be generated with as little as 75 mm (3 in) between the defined area and the machine frame or hard
(fixed) guarding.
Eliminate or reduce pass-through hazards whenever possible. While it is recommended to eliminate the pass-through
hazard altogether, this may not be possible due to machine layout, machine capabilities, or other application
considerations.
One solution is to ensure that personnel are continually sensed while within the hazardous area. This can be accomplished
by using supplemental safeguarding, such as described by the safety requirements in ANSI B11.19 or other appropriate
standards.
An alternative method is to ensure that once the safeguarding device is tripped it will latch and will require a deliberate
manual action to reset. This method of safeguarding relies upon the location of the reset switch as well as safe work
practices and procedures to prevent an unexpected start or restart of the guarded machine.
EZ-SCREEN
®
LP Limited Function Safety Light Screen
12
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