Calculation wizards

Basic principles regarding minimum distances (safety distances)

Electro-sensitive protective devices such as safety light curtains and safety laser scanners detect the approach of persons toward a point of operation. They do not prevent access to the point of operation, but from a sufficient distance from the point of operation they must cause the hazards to become ineffective in good time, e.g. cause movements to come to a standstill. The minimum distance is calculated in accordance with ISO 13855 as follows

S_RT [mm] = K [mm/ms] * T [ms] + C_RT [mm]

S_RT – minimum distance between the protective field and point of operation [mm]
K – approach speed: access by upper limbs: 2.0 mm/ms / entry: 1.6 mm/ms
T – stop time of the safety function after entry of the relevant part of the body into the protective field [ms]
C_RT – constant additional distance depending on the detection capability of the protective device [mm]

The minimum distance of electro-sensitive protective devices therefore consists of a constant (C) and a dynamic (K x T) component. As an electro-sensitive protective device too can be circumvented by reaching over, similar to guards the necessary height of the protective field must be determined from a table. The necessary distance to the point of operation therefore corresponds to the larger of the two values

S_RT (reach-through), calculated based on approach through the protective field
S_RO (reach-over), with CRO from the height of the top edge of the protective field and the height of the point of operation

The total stop time T can only be determined with sufficient accuracy by means of measurement. Special stopping time measuring devices are used for this purpose. Measurement of the stopping time is a service offered by Leuze. According to legal requirements, a safety inspection which also includes the stopping time measurement may be performed only by competent persons.

Stopping time measurement service

Wizards for calculating the minimum distance (safety distance) in accordance with ISO standards

The recommendations of this wizard do not lay any claim to being complete. To ensure correct safety-related use and mounting of the products, it is essential to observe the latest version of the respective standards and regulations. Leuze electronic GmbH + Co. KG assumes no liability for damage resulting from the use of this wizard or for the accuracy of the generally applicable standards and directives.

Calculation of the minimum distance (safety distance) with perpendicular approach and a resolution of ≤ 40 mm (ISO 13855)

The minimum distance S_RT is calculated using the following formula:

S_RT [mm] = (K[mm/ms] x T [ms]) + C_RT [mm]

S_RT: Minimum distance between the protective field and point of operation
K: Approach speed
T: Stopping time of the entire system
C_RT: Constant additional distance depending on the detection capability of the protective device: C_RT = 8 x (d[mm] – 14 mm)

Initially, the value of 2.0 mm/ms is used for K. If the calculation results in S_RT > 500 mm, the calculation may be repeated with K = 1.6 mm/ms. The result for S_RT must be at least 500 mm in the second step (if the calculated value is lower, S_RT is set to 500 mm).
Attention: The distance S to the point of operation must always be at least 100 mm, even if a lower value was calculated.

Calculation of the minimum distance (safety distance) with perpendicular approach and a resolution of > 40 mm (ISO 13855)

Note: This formula applies to multiple light beam safety devices, safety light curtains and safety laser scanners with corresponding resolution.

The minimum distance S_RT is calculated using the following formula:

S_RT [mm] = (K[mm/ms] x T [ms]) + 850 mm

S_RT: Minimum distance between the protective field and point of operation
K: Approach speed: 1.6 mm/ms
T: Stopping time of the entire system

S: Minimum distance
a: Height of the bottom beam above the reference plane
b: Height of the top beam above the reference plane

Note: The table value for C_RO (reach-over) must also be determined. This is usually greater than 850 mm!


Height of the danger zone	Height of top edge of protective field of electro-sensitive protective equipment
	900	1 000	1 100	1 200	1 300	1 400	1 600	1 800	2 000	2 200	2 400	2 600
	Additional distance to the danger zone C_RO
2 600	0	0	0	0	0	0	0	0	0	0	0	0
2 500	400	400	350	300	300	300	300	300	250	150	100	0
2 400	550	550	550	500	450	450	400	400	300	250	100	0
2 200	800	750	750	700	650	650	600	550	400	250	0	0
2 000	950	950	850	850	800	750	700	550	400	0	0	0
1 800	1 100	1 100	950	950	850	800	750	550	0	0	0	0
1 600	1 150	1 150	1 100	1 000	900	850	750	450	0	0	0	0
1 400	1 200	1 200	1 100	1 000	900	850	650	0	0	0	0	0
1 200	1 200	1 200	1 100	1 000	850	800	0	0	0	0	0	0
1 000	1 200	1 150	1 050	950	750	700	0	0	0	0	0	0
800	1 150	1 050	950	800	500	450	0	0	0	0	0	0
600	1 050	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

Calculation of the minimum distance (safety distance) for area guarding with parallel approach using a safety laser scanner (ISO 13855)

The minimum distance SRT is calculated using the following formula:

S [mm] = (K[mm/ms] x T [ms]) + C [mm] + Z [mm]

S: Minimum distance between the danger zone and detection point
K: Approach speed: 1.6 mm/ms
T_Scanner: Selectable response time of the RSL 400 safety laser scanner
T_Mach: Stopping time of the entire system

C: = 1200 mm - 0.4 * H
Safety-related constants for taking into account penetration into the danger zone before triggering the protective device. C_Min = 850 mm
H: Height of the protective field above the reference plane
H_Min = 15 * (d - 50), d = resolution of the protective device
H_Max = 1000

Z: Further additional distances with safety laser scanners

In the case of safety laser scanners, IEC 61496-3 states that additional distances have to be taken into account:

Z_SM for correction of the measurement error. This value is device-dependent and is given in the respective operating instructions. With the Leuze RSL 400 safety laser scanner, a Z_SM of 100 mm applies for a protective field radius ≤ 6.25 m and a Z_SM of 120 mm for a protective field radius > 6.25 m.
Z_REFL: Avoid using retro-reflectors in the beam plane beyond the protective field boundary. If this is not possible, an additional distance Z_REFL of 100 mm must be added.

Note regarding use on automated guided vehicles:
In accordance with ISO 3691-4 "Industrial trucks – Safety requirements and verification – Part 4: Driverless industrial trucks and their systems", testing of the protective device must also take into consideration the most unfavorable conditions (e.g. load, inclination of the transportation path) in combination with the parameters specified for the truck. The size of the protective field can increase as a result of these requirements.

Calculation of the minimum distance (safety distance) for area guarding with parallel approach using a safety light curtain (ISO 13855)

The minimum distance SRT is calculated using the following formula:

S [mm] = (K[mm/ms] x T [ms]) + C [mm]

S: Minimum distance between the danger zone and detection point
K: Approach speed: 1.6 mm/ms
T: Stopping time of the entire system

C: Safety-related constants for taking into account penetration into the danger zone before triggering the protective device.

C= 1200 mm - 0.4 * H, C_Min = 850 mm

H: Height of the protective field above the reference plane
Permissible mounting height:
H_Min = 15 * (d - 50), d = resolution of the protective device,
H_Max = 1000 mm

Required resolution d with mounting height H:
d [mm] ≤ (H/15) + 50 mm

Note: Heights > 300 mm are considered as possible for a person to crawl under.

The following table is used for determining the necessary height of a fixed guard for high-risk applications according to ISO13857.

Given are:

Height of danger zone (a)
Horizontal safety distance to danger zone (c)

To be determined:

The required height of the protective construction (b)
- Look for the line with the specification of the danger zone height in the left column.
- In this line, look for the column with the specification for horizontal safety distance to danger zone.
- The required height of the protective construction is up top in the column head. In case of interim values, the higher value of the protective construction must be used.


Height of the danger zone (a)	Height of the protective construction (b)
	1 000	1 200	1 400	1 600	1 800	2 000	2 200	2 400	2 500	2 700
	Horizontal safety distance to danger zone (c)
2 700	0	0	0	0	0	0	0	0	0	0
2 600	900	800	700	600	600	500	400	300	100	0
2 400	1 100	1 000	900	800	700	600	400	300	100	0
2 200	1 300	1 200	1 000	900	800	600	400	300	0	0
2 000	1 400	1 300	1 100	900	800	600	400	0	0	0
1 800	1 500	1 400	1 100	900	800	600	0	0	0	0
1 600	1 500	1 400	1 100	900	800	500	0	0	0	0
1 400	1 500	1 400	1 100	900	800	0	0	0	0	0
1 200	1 500	1 400	1 100	900	700	0	0	0	0	0
1 000	1 500	1 400	1 000	800	0	0	0	0	0	0
800	1 500	1 300	900	600	0	0	0	0	0	0
600	1 400	1 300	800	0	0	0	0	0	0	0
400	1 400	1 200	400	0	0	0	0	0	0	0
200	1 200	900	0	0	0	0	0	0	0	0
0	1 100	500	0	0	0	0	0	0	0	0

Obstacles with a height under 1000 mm are not included since they do not satisfactorily limit the movement.

Obstacles under 1400 mm should not be used without additional safety-related measures, since these obstacles are too easy to climb over.

ISO 13854 specifies – depending on the part of a person's body concerned – minimum distances between two moving machine parts or one moving and one fixed machine part which are not considered to pose a significant crushing risk. If these distances can be maintained during design of a machine, then no further protective measures are necessary here with respect to crushing risks, and openings of this size can be considered as inherently safe.

Required minimum distances for access with:

Finger	Hand	Arm	Toes	Foot	Leg	Head	Body
25 mm	100 mm	120 mm	50 mm	120 mm	180 mm	300 mm	500 mm

If for design reasons these distances cannot be observed, additional technical measures such as guards and electro-sensitive protective devices must be used to prevent access or to ensure prompt shutdown of the hazardous movements. They fulfill their protective function only if they are mounted at a minimum distance away from the point of operation to be guarded.

If guards are used in accordance with ISO 13857, the following aspects must be taken into consideration when determining the fixed value for the safety distance:

Opening sizes and penetration depths – safety distance depending on the part of the body concerned as given in a table
Reach-over – height of the protective device depending on the distance and height of the point of operation as given in a table
Crawl-under – gap below guards ≤ 180 mm