Overview - Versions With Sil Available; Az20 Safe Area Oxygen Analyzer; Az30 Hazardous Area Oxygen Analyzer; Acronyms And Abbreviations - ABB Endura AZ20 Manual

E N D U R A A Z 2 0 & A Z 3 0 | OX YG E N A N A LY Z E R | S I/A Z 2 0/A Z 3 0 - E N R E V. A
1 Overview – versions with SIL
available

AZ20 safe area oxygen analyzer

Figure 1 AZ20 remote version
Figure 2 AZ20 integral version
Identifier:
AZ20/xxxxxxxxxxxxx0xx/STD

AZ30 hazardous area oxygen analyzer

Figure 3 AZ30 remote version
Figure 4 AZ30 integral version
Identifier:
AZ30/xxxxxxxxxxxxxxxx/STD
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Acronyms and abbreviations

Safety Function

A defined function executed by a safety related system which is
intended to achieve or maintain a safe state in respect of a
specific hazardous event.

"Safe" Failure

A failure which forces the safety instrumented system into a
spurious annunciation state. This is usually synonymous with
the term "spurious trip".

Dangerous Failure

A failure which has the potential to put the safety instrumented
system in a dangerous or non-functioning state. This is usually
synonymous with the term "failure to trip"

Type A Subsystems

A subsystem is Type A if all of the following are true:-
The failure modes of all components are well defined
The behaviour of the subsystem under fault conditions can be
completely determined
There is sufficient dependable field failure data to show that
the claimed failure rates for detected and undetected
dangerous failures are met.

Hardware Fault Tolerance (HFT)

The ability to continue to provide a safety function in the
presence of faults and errors. A hardware fault tolerance of N
means that N+1 faults could cause the loss of a safety function.

Safe Failure Fraction (SFF)

The fraction of failures that does not have the potential to put
the safety instrumented system in a dangerous or non-
functioning state. This figure is sometimes expressed as a
percentage.

PFD The probability of failure on demand

This is intended to apply to systems operating in a low demand
mode where the safety function is required on average a
maximum of once per year.

Proof Test

Periodic tests that are performed to detect failures so that, if
necessary, the system can be restored to a fully working state.

Safety Integrity Level (SIL)

IEC 61508 defines four Safety Integrity Levels from SIL1 to SIL4.
Each of these corresponds to a range of probabilities that the
safety function will fail. The higher the SIL the lower the
probability of failure and the greater the probability that the
safety function will work when required to do so.
Table 1 on page 4 shows the dependency of the SIL on the
probability of failure on demand (PFD for low demand mode of
operation.
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