
NotE
When calculating the safety distance, also consider installation tolerances, accuracy of the measured response time and possible decay of the brake system performance of the machine.
It is advisable to increase the calculated value by at least 10% in order to take into account installation tolerances, accuracy in response time and possible degradation of brake system performance.
As can be seen from the formulas, the total stopping time plays an important role in calculating the safety distance; When a deterioration in braking time is expected, a Stopping Time monitoring device (SPM) is required. Checking of the stopping time is not necessary when:
- The system is very reliable and not subject to deterioration
- The machine is only rarely stopped
- Effective preventive control of the braking systems of the machine is implemented.
The effectiveness of the protection depends mostly on the correct positioning of the light curtain with respect to the danger.
The light curtain must be located at a distance greater or equal to the minimum safety distance, S, so that reaching the dangerous point will be possible only when the dangerous action of the machine has been stopped.
The light curtain must be positioned so that:
European Standard EN SO 13855 provides the elements for the determination of the safety distance.
If the machine is governed by a specific C type Standard, the latter shall be taken into due account.
If the calculated distances proves excessive, it is necessary to: |
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GENERAL FORMULA FOR THE DETERMINATION OF THE MINIMUM SAFETY DISTANCE
S = K x T + C |
S | minimum safety distance between the protection and hazardous point, expressed in mm. |
K |
speed of approach of the body or parts of the body, expressed in mm / sec. |
T | total stopping time of the machine, consisting of: t1 reaction time of the protective device in seconds t2 reaction time of the machine in seconds, until it stops the hazardous action. |
C | additional distance in mm. |
DIRECTION OF APPROACH PERPENDICULAR TO THE PROTECTED PLANE WITH Α=90° (± 5°) | ||
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Light curtains with resolution for the detection of hands and fingers. Light curtains resolution (d): 14 - 20 - 30 - 40 mm |
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1. Hazardous point |
Determination of the minimum safety distance: S = K x T + C
S=2000xT+8x(d-14)
S=1600xT+8x(d-14) |
K = 2000 or 1600 (see following
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Light curtains with a resolution for detection of arms and legs. Light curtains resolution (d): 50 - 90 mm | |
1. Hazardous point |
Determination of the minimum safety distance: S = K x T + C
S= 1600xT + 850 |
K = 1600
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Possibility to reach the hazardous point by leaning over the edge of the sensitive area |
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1. Hazardous point |
Determination of the minimum safety distance: S = K x T + C
S= KxT + CR0
Note:
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In this case C, called “CRO” is obtained from the following Table 1 of ISO 13855:2010.
K = 2000 or 1600 (see following calculations)
T = t1 + t2 “General formula for the |
Height of |
Height “b” of upper edge of area protected by photoelectric light curtain | |||||||||||
900 | 1000 | 1100 | 1200 | 1300 | 1400 | 1600 | 1800 | 2000 | 2200 | 2400 | 2600 | |
Alternative distance CR0 | ||||||||||||
2600 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
2500 | 400 | 400 | 350 | 300 | 300 | 300 | 300 | 300 | 250 | 150 | 100 | 0 |
2400 | 550 | 550 | 550 | 500 | 450 | 450 | 400 | 400 | 300 | 250 | 100 | 0 |
2200 | 800 | 750 | 750 | 700 | 650 | 650 | 600 | 550 | 400 | 250 | 0 | 0 |
2000 | 950 | 950 | 850 | 850 | 800 | 750 | 700 | 550 | 400 | 0 | 0 | 0 |
1800 | 1100 | 1100 | 950 | 950 | 850 | 800 | 750 | 550 | 0 | 0 | 0 | 0 |
1600 | 1150 | 1150 | 1100 | 1000 | 900 | 800 | 750 | 450 | 0 | 0 | 0 | 0 |
1400 | 1200 | 1200 | 1100 | 1000 | 900 | 850 | 650 | 0 | 0 | 0 | 0 | 0 |
1200 | 1200 | 1200 | 1100 | 1000 | 850 | 800 | 0 | 0 | 0 | 0 | 0 | 0 |
1000 | 1200 | 1150 | 1050 | 950 | 750 | 700 | 0 | 0 | 0 | 0 | 0 | 0 |
800 | 1150 | 1050 | 950 | 800 | 500 | 450 | 0 | 0 | 0 | 0 | 0 | 0 |
600 | 1050 | 950 | 750 | 550 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
400 | 900 | 700 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
200 | 600 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
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For combined mechanical and electrosensitive protections (as shown), where it would be possible to lean against the mechanical protection and bypass the light curtain | |
1. Hazardous point |
For the calculation of the parameter C should use
of ISO 13857:2007 (formerly EN 294) in place of the table on the previous page.
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Light curtains for the detection of the presence of the body in a dangerous area. Light curtains with 2 - 3- 4 beams |
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1. Hazardous point |
Determination of the minimum safety distance: S = K x T + C
S= 1600xT + 850 Note for 2 beams light curtains:
Note for 3 beams light curtains:
Note for 4 beams light curtains:
Height of the beams from the reference plane (eg. floor). |
K = 1600
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DIRECTION OF APPROACH PARALLEL TO THE PROTECTED PLANE WITH Α=0° (± 5°) | ||
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Horizontal light curtains for presence control in a dangerous area | |
![]() 2. Sensitive area 3. Reference plane a. Height of the hazardous point x. Distance between end of the detection zone and machine edge S. Safety distance H. Height of the sensitive area |
Determination of the minimum safety distance: S = K x T + C
S= 1600xT + (1200-0,4xH)
Note:
When using the light curtain as a combination of trip and presence sensing device, the distance x must be less than or equal to the detection capability |
K = 1600
T = t1 + t2 “General formula for the
C = 1200 - (0,4 x H) |
DIRECTION OF APPROACH ANGLED TO THE PROTECTED PLANE WITH 5°< Α <85° | ||
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Slanted light curtains to detect hands and arms and for presence control in the dangerous area | |
1. Hazardous point |
With angle α >30° refer to the case of “APPROACH PERPENDICULAR TO THE PROTECTED PLANE”. Note:
With angle α <30° refer to the case of “APPROACH PARALLEL TO THE PROTECTED PLANE”.
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