Oldham MX62, Руководство пользователя

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Page 73
14.5. Failure rates for WinPro / MX62 (PFD value)
For integration in a safety related system, additional to the SIL capability a value
for probability of failures in alarm state is needed. This value is named PFD
(Probability of Failure on Demand).
The maximum PFD value is defined for a complete safety chain. For SIL 2 is
PFD < 10
-2
and for SIL 3 is PFD < 10
-3
.
There is a general agreement that 35% of the maximum PFD value is assigned to
the detector, 15% to the control unit (WinPro) and 50% to the actor part of the
safety chain. This leads to following PFD values for WinPro:
SIL 2 < 1.5 x 10
-3
SIL 3 < 1.5 x 10
-4
WinPro

/ MX62 is a partly redundant system with redundant and non-
redundant functions. These functions have been validated separately in an
FMEDA study. The following PFD values have been calculated from it.
For the calculation of PFD an average repair time (MTTR) of 72 hours is
assumed. The PFD is calculated for proof test intervals (T1) of one, two and
three years.

PFD value for a simple safety chain with an input of one connected detector
and an output of one assigned relay contact:
a) With a proof test interval of one year:
PFD = 5.24 x 10
-4
b) With a proof test interval of two years:
PFD = 1.03 x 10
-3
c) With a proof test interval of three years:
PFD = 1.54 x 10
-3

PFD value for a fully redundant safety chain with an input of two redundant
detectors for one detection point and an output of two assigned separate relay
contacts:
a) With a proof test interval of one year:
PFD = 2.95 x 10
-5