8
Recommended Fc factors are listed in the table below:
ENVIRONMENTAL CONDITION CORRECTION FACTOR Fc
Mist 0,25
Vapours 0,50
Dust 0,50
Dense fumes 0,25
SAFETY DISTANCE AND POSITIONING
The photocell must be installed at a distance greater than or equal to the minimum
safety distance, S, so that no hazardous point can be reached until the hazardous action
of the machine has stopped (fig. 2).
Figure 2
With reference to European standard prEN999, the minimum safety distance, S, must be
calculated through the following formula:
S = K(tb + tu + t1 ) + C
where:
S is the minimum safety distance expressed in mm.
K is the speed of approach of the body to the hazardous zone in mm/sec.
tb is the reaction time of the barrier (≤ 7ms, single beam; ≤ 14ms, double beam).
tu is the reaction time of the control unit (≤ 15ms).
t1 is the reaction time of the machine in seconds, i.e., the time it takes the machine to
stop the hazardous action from the time the control unit transmits the stop signal
through the opening of its output circuit.
C is an additional distance in mm.
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