Functional Safety 2016

Functional Safety 2016

November, 2016 - London

Page 5 of 17

How to Calculate PFD

AVG

and PFD

AVG

including

PFD

AVG

for a basic 1oo1 system including C

!"#

!"#$%

× 2

!"#$%

× 1 −

× 2

(1)

(Abdelrhafour, Bajaj, & Boily, 2012)

Where:

!"#$%

is the total dangerous undetected failure rate;

is the proof test coverage;

is the proof test interval

is the mission time of the equipment

is calculated by:

!"#$%&'&#" !" !"

!"#$%

(2)

(Abdelrhafour, Bajaj, & Boily, 2012)

Where:

!"#$%&'&#" !" !"

is the dangerous undetected failure rate identified by the proof test.

is undetected dangerous failure rate

is dangerous systematic failure rate

Table 1: Simplified 1oo1 PFD

AVG

Equations

Architecture

Simplified PFD

AVG

1oo1

×!" !

(ISA, 2002)

(3)

1oo1 including

!"#

!" !"#$%

×!

×!"

!" !"#$%

× !!!

×!"

(Abdelrhafour, Bajaj, & Boily, 2012)

(4)