Compur Monitors Statox 506 - Failure Rates and Safe Failure Fraction; Probability of Failure on Demand; Safety Integrity Level (SIL) Classification; Product Lifetime Information

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11.6 Failure Rates and Safe Failure Fraction
A FMEDA-Hardware-Assessment, performed by SGS-TÜV Saar GmbH, test report M2L50001, resulted
in these performance data:
λ
s
[FIT]
λ
du
[FIT]
λ
dd
[FIT]
λ
don´t care
[FIT]
SFF [%]
Statox 506 transmitter without sensor
304,64
42,38
271,31
21,00
93,1
Statox 506 inclusive sensor resulted in these performance data:
λ
du
[FIT]
SFF [%]
Statox 506 Transmitter with Cl
2
Sensor
70,95
97,8
Statox 506 Transmitter with HCN Sensor
131,77
91,9
Statox 506 Transmitter with COCl
2
Sensor
124,60
96,9
Statox 506 Transmitter with H
2
S Sensor
117,91
97,8
Statox 506 Transmitter with CO Sensor
141,82
96,3
11.7 Average Probability of Failure on Demand
Statox 506 has been designed and is classified to be a gas detector with low demand.
Transmitter and sensor are considered as a complex system type B according to standard IEC 61508-
2:2010.
The PFD
avg
-values have been calculated with this formula: PFD
avg
= 0.5
*
T
Proof *
λ
du
.
Basic assumption is that the repair time is significantly shorter than the prooftest interval.
The sensor operation time is 1 year (best before), for COCl
2
sensors ½ year. After this time interval the
sensor must be replaced or calibrated.
PFD
avg
for
T
Proof
= 6 months
PFD
avg
for
T
Proof
= 12 months
Statox 506 Transmitter with Cl
2
Sensor
3,11 x 10
-4
Statox 506 Transmitter with HCN Sensor
5,77 x 10
-4
Statox 506 Transmitter with COCl
2
Sensor
2,73 x 10
-4
Statox 506 Transmitter with H
2
S Sensor
5,16 x 10
-4
Statox 506 Transmitter with CO Sensor
6,21 x 10
-4
PFD
avg
: Average Probability of Dangerous Failure on Demand
11.8 Classification of the Safety Integrity Level (SIL)
As specified in standard IEC 61508-2:2010 table 3, with a hardware failure tolerance (HFT) = 0 and a
SFF of > 90 % the Statox 506 inclusive sensor complies with the requirements for a SIL 2 rating.
11.9 Lifetime
The transmitter lifetime without sensor is determined to be 10 years. Within this lifetime period the above
mentioned failure rates are valid without being too optimistic.