KROHNE OPTISWITCH 3x00C Relay SIL EN - Manual (Page 6)

Number values see chapter "Safety-related characteristics".
If the "low demand rate" does not apply, the measuring system
as safety-relevant subsystem in "high demand mode" should
be used (IEC 61508-4, 3.5.12).
The fault tolerance time of the complete system must be higher
than the sum of the reaction times or the diagnostics test
periods of all components in the safety-related measurement
chain.
An associated characteristic is the value PFH (failure rate).
Number values see chapter "Safety-related characteristics".
The following assumptions form the basis for the implemen-
tation of FMEDA:
l
Failure rates are constant, wear of the mechanical parts is
not taken into account
l
Failure rates of external power supplies are not taken into
account
l
Multiple errors are not taken into account
l
The average ambient temperature during the operating
time is 40 °C (104 °F)
l
The environmental conditions correspond to an average
industrial environment
l
The lifetime of the components is around 8 to 12 years
(IEC 61508-2, 7.4.7.4, remark 3)
l
The repair time (exchange of the measuring system) after
an nondangerous malfunction is eight hours (MTTR = 8 h)
l
The processing unit evaluates the output circuit of the
measuring system according to the quiescent current
principle.
l
The scanning interval of a connected control and pro-
cessing unit is max. 1 hour, in order to react to dangerous,
detectable errors
l
Existing communication interfaces (e. g. HART, I²C-Bus)
are not used for transmission of safety-relevant information
The measuring system should be used appropriately taking
pressure, temperature, density and chemical properties of the
medium into account.
The user-specific limits must be kept. The specifications of the
operating instructions manual must not be exceeded.
Keep in mind when using as dry run protection:
High demand mode
Assumptions
General instructions and
restrictions
6 OPTISWITCH series 3000 • - Relay (DPDT)
Functional safety
32743
-EN
-080414