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Copyright © 2014 by Cenbee Bullock PFS Consulting Ltd
PFS
Specialising
In Functional Safety
Minimising Systematic Failures in SIS Design
When may systematic failures be introduced?
PFDsystematic failure
=
PFDsys-process plant
+
Psys-human error
Mathematical analysis formulae (TR84.00.02-2):
PFDSIF =
ƩPFDsensor
+
ƩPFDlogic solver
+
ƩPFDfinal element
+
ƩPFDpower supply
+
ƩPFDsystematic failures
Psys-human error =
Pdesign error
+
Pinstallation
+
Pproof test error
+
Pbypassed
ISA-TR84.00.02-2002 Part 2
“Systematic failures may be introduced during the specification, design,
implementation, operational and modification phase and affect hardware
as well as software.”