BERTHOLD TECHNOLOGIES LB4710-080 - 3.2 Safety Function; 3.3 Safety Requirement; 3.4 Project Planning

Chapter 3 Functional Safety
Mini-Switch LB 471
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3.2 Safety Function
The safety function of the measuring system comprises the detec-
tion and indication of changes in the count rate of the detectors
caused by the presence of product being measured in the measur-
ing path between radiation source and measuring system.
The safe status is dependent on the mode of operation:
 Maximum level (overflow protection): Product between radia-
tion source and detector -> low count rate
 Minimum level (protection against running dry): No product
between radiation source and detector -> high count rate
3.3 Safety Requirement
Safety integrity
level
Operating mode with
low demand rate
Operating mode with high
or continuous demand rate
SIL
PFD
avg
PFH
4
≥10
-5
to <10
-4
≥10
-9
to <10
-8
3
≥10
-4
to <10
-3
≥10
-8
to <10
-7
2
≥10
-3
to <10
-2
≥10
-7
to <10
-6
1
≥10
-2
to <10
-1
≥10
-6
to <10
-5
Safe failure fraction
Hardware fault tolerance
SFF
HFT = 0
HFT = 1
HFT = 2
none: <60%
not allowed
SIL 1
SIL 2
low: 60% to <90%
SIL 1
SIL 2
SIL 3
medium: 90% to <99%
SIL 2
SIL 3
high: ≥99%
SIL 3
3.4 Project Planning
 Please make sure that the measuring system will be used in
accordance with its designated function.
 The application-specific limits have to be observed and the
specifications must not be exceeded. See also the technical da-
ta and ambient conditions in the User’s Manual.
 The fault tolerance time of the overall system must be greater
than the reaction time of the measuring system.
 The relay contacts have to be protected by a 1A fuse.
 The digital inputs 1 and 2 must not be closed in case of a safe-
ty-related application.
General instructions and
restrictions