Did you know...? | FAQ & Interesting Facts

...and how the risk time affects the distance to the hazardous area?

Application: SAFIX, Safety Light Curtain, Safety Simplifier

The standard EN ISO 13855:2010 describes the arrangement of protective devices in relation to the approach speed of human bodies. This standard helps to define the minimum safety distance to a dangerous movement when a guard is used without guard locking. The distance is calculated as shown in the following diagram.

Example calculations of the risk time

S= K * T

S= Distance to danger point

K= Constant = 1600 mm/s

T= Total time to standstill

In the next section, we will compare the risk time of our SAFIX 3 RFID safety sensors and HOLDX R process guard locking systems with commonly used market-standard sensors and locking systems. This comparison will focus on how the reaction times influence the distance to the danger zone (without any series connection).

Example

RFID safety sensor SAFIX 3 or process guard locking HOLDX R
Switch-off delay (toff) actuator to OSSD output:
max. 75 ms

Example

Standard RFID safety sensor or process guard locking
Switch-off delay (toff) actuator to OSSD output:
max. 260 ms

S = 1600 mm/s * 75 ms S = 120 mm

S = 1600 mm/s * 260 ms S = 416 mm

By using a risk time of 75 ms, a safety distance of 120 mm is established. For precise calculations, the risk time of the evaluation unit (e.g. safety controller) and the after-run time until complete stop must also be added.

The calculation shows that by setting a risk time of 260 ms, a safety distance of 412 mm is maintained. This corresponds to an additional safety distance of 292 mm compared to the previous calculation. For machine construction, this can be a crucial factor.

When safety sensors are connected in series, the calculation must also include the risk time of the inputs shutdowns. In the following example, 24 sensors are connected in series.

Example

RFID safety sensor SAFIX 3 or process guard locking HOLDX R
1 x Switch-off delay (toff) actuator to OSSD output: max. 75 ms
23 x Switch-off delay (toff) inputs: max. 3ms

Example

Standard RFID safety sensors or process guard locking devices
1 x Switch-off delay (toff) actuator to OSSD output: max. 260 ms.
23 x switch-off delay (toff) inputs: max. 20 ms

T = 75 ms + 23 * 3 ms T = 144 ms
S = 1600 mm/s * 144 ms S = 230,4 mm

T = 260 ms + 23 * 20 ms T = 720 ms
S = 1600 mm/s * 720 ms S = 1152 mm

For correct calculation, you must also add the risk time of the evaluation unit (e.g. safety control) and the after-run time until the system stops.

Products

Safety Sensor SAFIX

Process Guard Lock with RFID - HOLDX R