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4-4 Minimum Safe Mounting Distance and Mounting Height
4-4 Minimum Safe Mounting Distance and Mounting Height
The proper calculation of the safe mounting distance is an important installation step. Never just install a
F3SS at any convenient location without regard to the safety distance. If the emitter and receiver are
mounted too close to the point of operation hazard, the machine may not stop in time to prevent operator
injury.
The best information available on safe mounting distance and mounting height comes from the preliminary Eu-
ropean standard EN999:1998 sections 6.1.4 and 6.1.5.
Section 6.1.5 suggests that single height beams should only be considered where they are parallel to the ground
and the beam is broken by a person's body in the upright position.
Where the risk assessment allows a single height beam to be used alone then the minimum distance shall be
calculated using the following formula:
S = (K x T) + C
Where:
S = the minimum distance from the danger zone to the detection point, line, plane or zone;
K = a parameter in mm(inches) per second, derived from data on approach speeds of the body or parts of the
body. It is recommended that a minimum value of 1600mm/sec(63 in/sec) be used. Faster speeds may be war-
ranted. To quote from ANSI standard B11.19-1990, "The value of the hand speed constant, K, has been deter-
mined by various studies and although these studies indicate speed of 1600mm/sec(63 in/sec) to over 2450mm/
sec(100 in/sec), they are not considered conclusive determinations. The user should consider all factors, includ-
ing the physical ability of the operator, when determining the value of K to be used."
T = the overall system stopping performance(second). T must include the response time of controls, clutches,
braking systems and the F3SS (35 mS) and the time for the machine to cease hazardous motion. Add a per-
centage increase factor as recommended by the machine manufacturer, to allow for deterioration of the clutch
and braking system.
C = an additional distance in mm(inches), based on intrusion towards the danger zone prior to the actuation of
the protective equipment. In the case of the F3SS, 1200mm(48 inches)
Example:
S = (1600mm/sec x 0.250sec) + 1200mm
= 400mm + 1200mm
= 1600mm(63.75in)
When using a single beam, a mounting height of 750mm(29 inches) from the ground or reference plane has
been found in industry to be a practical solution to the problems of inadvertent access from stepping over or
bending under the beam.
When multiple single beams are employed, the following table presents beam mounting heights which have
been found to be practical in application:
Number of Beams
2
3
4
WARNING
Table 4-1 Practical Beam Mounting Heights
Heights above reference plane, such as floor: mm(inches)
300, 700, 1100(12, 28, 43 )
300, 600, 900, 1200(12, 24, 36, 48 )
400, 900(16, 36 )
4 Installation
7
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