NORSTAT Safety Relays - Handbuch (Seite 12)

application guide safety relays from riese electronic page 12
2 The replacement of EN 954-1
Previously, the machine constructing engineer had, according to the EN 954-1 (safety-related parts of
control systems, part 1: General design principles) to proof the compliance of the general safety
requirements according to the European machinery directive.
This standard demanded a risk analysis with the resulting safety categories (B, 1, 2, 3, 4). B stands for
low and almost no safety respectively, 4 stands for high safety. The safety devices for a system were
chosen with the safety category.
The EN 954-1 was replaced because programmable electronic systems were considered insufficiently
and the time response (e.g. testing intervals, life cycles) and the failure probability of components were
not considered. The following
standards EN 13849-1 (safety of machines – safety-related parts of control
systems, part 1: General design principles) and EN 62061 (safety of machines – functional safety of
electrical, electronic and programmable electronic control systems) create remedy and consider the
above approaches.
3 Definition of the safety requirements
It is divided into two parts: Safety of machines and the functional safety.
Safety of machines
Functional safety
3.1 Safety of machines
After finished risk evaluation according to EN ISO 14121-1, measures for reducing of the
detected risks will be defined. Afterwards, the risks will be reduced up to an acceptable residual
risk.
3.2 Functional safety
The functional safety follows from the results of the machinery safety. The functional safety is
divided into 6 steps:
NORSTAT INC. 300 Roundhill Dr. Rockaway, NJ 07866 Tel: 973-586-2500 Fax: 973-586-1590 www.norstat.com