Omni8/16C/Omni8P User Manual
UMC1480R24.pdf
72
© Omniflex 2021
Table 7-2 – Omni16 Safety Parameters
Subsystem
Type B
Hardware Fault Tolerance
0
DC
78%
SFF
83%
MTTR
8 hours
Proof Test Interval
1 year
PFD
avg
, (TI = 1 year)
2.02 x 10
-3
Safe failures detected λ
SD
495.5 FIT
Safe failures undetected λ
SU
192.1 FIT
Dangerous failures detected λ
DD
1623.0 FIT
Dangerous failure undetected λ
DU
458.8 FIT
An MTTR of 8hrs was used in the above PFD calculations.
Table 7-3 – Key to Abbreviations
DC = Diagnostic Coverage
λ = failure rate per billion hours (1 FIT = 1 failure in
10
9
hours)
SFF = Safe Failure Fraction
Failure Rate Categories:
PFD = Probability of Failure on Demand
SU = Safe Undetected
TI = Proof Test Interval
SD = Safe Detected
MTBF = Mean Time Between Failures
DU = Dangerous Undetected
MTTR = Mean Time To Repair
DD = Dangerous Detected
7.5
Diagnostics
There are two methods used to indicate internal failure detected in the unit:
The unit flashes alarm windows in specific pattern, thus identifying the circuit section that failed.
For other general hardware failures alarm indication is used. If input is in normal state then flashing
window, activated audible alarm or open GA contacts all indicate failure. In such cases alarm
indication typically cannot be acknowledged and reset.
For other general failures when abnormal operation is detected, Omni16C diagnostic watchdog contacts
change to open. This mainly indicates CPU board failures. To fully benefit from diagnostics, the state of
watchdog should be monitored.
