KROHNE H250 M40 Safety V1 EN - Manual (Page 4)

2
TERMS AND DEFINITIONS
4
H250 M40
www.krohne.com 02/2012 - 4000904201 MA H250 M40 SIL R01 en
Terms and definitions
Terms and definitions
2.1 Description of the considered profiles
Mechanical database
Electronic database
DC
D
Diagnostic Coverage of dangerous failures
FIT Failure In Time (1x10 -9 failures per hour)
FMEDA Failure Modes, Effects and Diagnostic Analysis
HFT Hardware Fault Tolerance
Low demand mode Mode, where the frequency of demand for operation made on a safety-related
system is not greater than one per year and not greater than twice in the proof test
frequency.
PFD
AVG
Average Probability of Failure on Demand
SFF Safe Failure Fraction summarizes the fraction of failure, which lead to a safe state
and the fraction of failures which will be detected by diagnostic measures and lead
to a defined safety action.
SIF Safety Instrumented Function
SIL Safety Integrity Level
Type A component "Non-complex" subsystem (all failure modes are well defined); for details see
7.4.3.1.2 of IEC 61508-2.
Type B component "Complex" subsystem (all failure modes are well defined); for details see 7.4.3.1.2
of IEC 61508-2.
T[Proof] Proof Test Interval
Profile Profile according to
IEC 60654-1 Ambient temperature [°C] Temperature cycle
[°C / 365 days]
Average (external) Mean (inside box)
2 C3 25 30 25
4 D1 25 30 35
Profile 2 (low stress): Mechanical field products with minimal self heating, subject to daily
temperature swings.
Profile 4 (high stress): Unprotected mechanical field products with minimal self heating,
subject to daily temperature swings and rain or condensation.
Profile Profile according to
IEC 60654-1 Ambient temperature [°C] Temperature cycle
[°C / 365 days]
Average (external) Mean (inside box)
2 C3 25 30 25
Profile 2 Low power electrical (2-wire) field products have minimal self heating and are
subjected to daily temperature swings.
MA_H250_M40_SIL2_R01_en_904201_PRT.book Page 4 Thursday, March 1, 2012 10:08 AM