KROHNE OPTISWITCH 5xx0C Relay SIL EN - Manual (Page 6)

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 implementation 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 processing unit
is max. 1 hour, in order to react to dangerous, detectable errors
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:
l
Avoid buildup on the vibrating system (probably shorter proof test
intervals will be necessary)
l
Avoid solids > 5 mm (0.2 in) stored in the medium
l
Avoid foam generation with a density of > 0.5 g/cm³ (0.018 lbs/in³)
1 .3 Adjustment instructions
Since the plant conditions influence the safety of the measuring
system, the adjustment elements must be set according to the
application:
l
DIL switch for mode adjustment
l DIL switch for sensitivity adjustment
High demand mode
Assumptions
General instructions and
restrictions
Adjustment elements
6 OPTISWITCH series 5000 • - relay (DPDT)
1 Functional safety
32748
-EN
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