15 Appendix
15.4 Safety technology glossary
Term/abbreviation Description
CCF Common cause failure in accordance with EN ISO 13849-1.
DC avg Average diagnostic coverage in accordance with IEC 61508
and EN 61800-5-2.
HFT Hardware fault tolerance in accordance with IEC 61508.
Cat. Safety category in accordance with EN ISO 13849-1, level 1-
4.
MSC MetronixServoCommander
®
, software for configuration and
start-up.
MTTFd Mean time to dangerous failure. Time in years until the first
dangerous failure will have occurred with 100% probability, in
accordance with EN ISO 13849-1.
Emergency off In accordance with EN 60204-5-1 Electrical safety is
ensured in case of an emergency by switching off the
electrical energy supply to the entire installation or part of it.
An emergency off is to be used where a risk of electric shock
or other electrical risk exists.
Emergency stop In accordance with EN 60204-5-1 In an emergency,
functional safety is ensured by stopping a machine or
moving parts.
An emergency stop is used to stop a process or a movement
which has become hazardous.
OSSD Output signal switching device, output signals with 24 V
level cycle rates for error detection.
PFD Probability of failure on demand in accordance with IEC
61508.
PFH Probability of dangerous failures per hour in accordance with
IEC 61508.
PL Performance level in accordance with EN ISO 13849-1:
Levels a to e
PWM Pulse width modulation. Stands for the digital actuation of
the power semiconductors with a variable duty cycle in order
to adjust a voltage at the motor output.
SFF Safe failure fraction [%], ratio between the failure rates of
safe and dangerous (but recognisable) failures and the total
number failures in accordance with IEC 61508.
Safety relay Device for executing safety functions or for establishing a
safe state of the machine by switching off the energy supply
for dangerous machine functions. The desired safety
function can be achieved only in combination with other risk
reduction measures, e.g. by switching off a servo drive.
Product manual BL 4000-C Page 264 of 298
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