NORSTAT Safety Relays - Handbuch (Seite 7)

application guide safety relays from riese electronic page 7
indicator against penetration of water. The higher the number is the higher is the
respective protection. Protection classes from IP65 became accepted as standard
in industrial environments.
Light curtain A light curtain consists of a multiple number of lined up light barriers, so that the
danger zone can be supervised consistently. If the light curtain is mounted near the
danger zone, a lower resolution, viz. less light barriers per unit of length, is required
than with bigger distances. There are several types: Light curtains for finger guard
(14 mm of resolution) or hand guard (30 mm of resolution) as well as for body
protection (2 - 4 beams).
Light grid Multibeam configuration of one way light barriers in one housing.
Light barrier, oneway A light barrier with which the light of the light transmitter is leaded to an optical and
special separated light receiver.
λ (Failure Rate) Probability of a failure
λ avg (Failure
Rate,average) Average probability of a failure per hour
λ DD (Failure
Rate,dangerous,
detected) Dangerous, detected failure
λ DU (Failure Rate,
dangerous undetected) Dangerous undetected failure
λ SD (Failure Rate,safe,
detected) Safe detected failure
λ SU (Failure Rate,safe,
undetected) Safe undetected failure
Machinery safety After done risk analysis by implemented action achieved minimization
of risk on an accepted remaining risk
MTBF (Mean Time
Between Failures) Mean time between two failures
MTTF (Mean Time To
Failure) Mean time to failure
MTTFd (Mean Time To
Dangerous Failure) Mean time to dangerous failure
Muting Bypass function: A time limited automatic bypass function of the safety function
with additional sensor technology, to differ persons from objects
OR operation Connects two or more units. Start-up occurs when at least one of the start-up
conditions is met.
OSSD (Output Signal
Switching Device) Output circuit of an ESPE, which is connected to the machine control and switches
in den off-state, as soon as the sensor function acts during the intended operation.
Performance Level Ability of safety related parts to run a safety function under predictable conditions to
achieve the expected reduction of risk.
PFD Probability of Failure on Demand
PFDavg Average Probability of Failure on Demand
PFH Probability Of Failure Per Hour
PFHd Probability Of Dangerous Failure Per Hour
Readiness delay time Readiness delay time is the time, between applying the supply voltage and the
output of the right switching signal.
Redundancy The application of more than one identical element, in order to ensure that if one
element malfunctions, a second element is available to guarantee that the safety
function is maintained.
Reaction time After supply voltage is applied, the period that elapses before the unit is ready for
operation.
Safety Integrity Average probability, that a safety related system executes the required safety
related functions among all specified conditions within an agreed period of time.
Safety Integrity Level One out of 4 discrete steps for the specification of the requirements for the safety
integrity of the safety function, which are assigned to a safety-related system.
Safety integrity level 4 represents the highest and safety integrity level 1 the lowest
safety level.
Safe output see OSSD
SFF (Safe Failure
Fraction) The part of safe failures, viz. the rate of failures which direct into the fail safe
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