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Sizing Your System
The following formula is an international draft guideline for the proper positioning and application of safety mats for machine guarding. This formula must be followed for all safety mat applications supplied to the European Community (CE) member nations. CEN is the European Committee for Standardization. Final draft #prEN999
The minimum distance from the danger zone shall be calculated by using the general formula: S=(K x T) +C where:
S is the safety mat minimum distance in inches/millimeters in a horizontal plane, from the danger zone to the detecting edge of the safety mat furthest from the danger zone.
K is a parameter in inches/millimeters per second, derived from data on approach speeds of the body or parts of the body. K=63 inches/second or 1600mm/second.
T is the total system stopping time performance in seconds, which includes activating the safety mat, the mat controller output signal switching device and the time required to stop the machine and remove risk. The activation time of the STTS Safety Mat System including controller is 35 msec (.035 seconds). This amount must be added to the machine stopping time to fulfill the "T" requirements.
C is an additional distance in inches/millimeters, based on intrusion towards the danger zone prior to actuation of the protective safety mat equipment. C=48 inches or 1219mm.
Walking speeds and stride lengths.
The positioning of equipment which is activated by a person walking into the detection zone by stepping onto a pressure sensitive mat is affected by speed of approach and stride length. The walking speed and stride length depend on the physical and anthropometric data of the population.
This standard assumes the approach of persons towards the danger zone will be at walking speed.
Available research data has shown the 95th percentile of two steps (i.e., starting and finishing with the same foot) measured from heel contact at walking speed is approximately 75 inches/1900 mm. By dividing by 2 and subtracting the 5th percentile shoe length, this gives a stride length of 28 inches/700 mm. If it is assumed that an allowance has to be made, for example, between the detection zone and the stride length of 2 inches/50 mm, this gives a minimum width of 30 inches/750 mm for the detection zone.