63
Safety Manual
00809-0200-5100, Rev GB
Terms and Definitions
February 2017
Terms and Definitions
Section 6 Terms and Definitions
BPCS Basic Process Control System
Demand rate How often it will be required from a safety integrity system (or the
safety function) to react on inputs from process to bring it into a safe
state, i.e. to issue an alarm
FIT Failure in Time (1 FIT = 1failure/10
9
h)
FMEDA Failure Modes, Effects and Diagnostics Analysis
HFT Hardware Fault Tolerance
High mode of operation The safety function is only performed on demand, in order to transfer
the EUC into a specified safe state, and the frequency of demands is
greater than one per year
Low mode of operation The safety function is only performed on demand, in order to transfer
the EUC into a specified safe state, and the frequency of demands is
no greater than one per year
Mode of operation The way in which a safety function operates, which may be either low
mode of operation or high mode of operation
PFD
avg
Average probability of Failure on Demand
PFH (average frequency
of a dangerous failure
per hour)
Average frequency of a dangerous failure of an E/E/PE safety related
system to perform the specified safety function over a given period of
time
SFF Safe Failure Fraction summarizes the fraction of failures, 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
SIL Reference Point The SIL Reference Point is located at the flange of the 5900 Radar
Level Gauge. It used as reference point for the SIL High and Low Alarm
Limits.
SIS Safety Instrumented System
Type B component Complex component (using micro controllers or programmable
logic)
1oo1D Architecture consisting of a single channel with additional diagnostic
capabilities.
1oo2D Architecture consisting of two channels (level gauges) connected in
parallel with additional diagnostic capabilities. During normal
operation the system goes to alarm if either channel (level gauge)
indicates an alarm condition
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