WIKA T32.xS - Manual (Page 5)

GB
5 WIKA safety manual temperature transmitter T32.xS
11583631.03 08/2014 GB/D/F/E
1.3 Relevant standards
Standard Model T32.xS
IEC 61508:2010 Functional safety of safety-related electrical/electronic/
programmable electronic systems
Target group: Manufacturers and suppliers of instruments
IEC 61511:2004 Functional safety: safety instrumented systems for the process
industry
Target group: designers, integrators, users
1.4 Abbreviations and terms
Abbreviation Description
λ
SD
+ λ
SU
λ
SD
safe detected + λ
SU
safe undetected
A safe failure is present when the measuring system switches to the
defined safe state or the fault signalling mode without the process
demanding it.
λ
DD
+ λ
DU
λ
DD
dangerous detected + λ
DU
dangerous undetected
Generally a failure to danger occurs if the measuring system,
through this, can switch into a dangerous or functionally
inoperable condition. With detected failures to danger, the failure
is detected by diagnostic tests or proof testing, for example, where
the system switches to the safe state. With undetected failures to
danger, the failure is not detected through diagnostic tests.
Operating
mode with low
demand rate
In this operating mode, the safety function of the safety system
is only carried out on request. The frequency of the request is no
more than once a year.
DC Diagnostic coverage, percentage of failures to danger that are
detected by automatic diagnostic online tests.
FMEDA Failure modes, effects and diagnostic analysis, methods to detect
failure causes, and also their impact on the system, and to define
diagnostic measures.
HFT Hardware fault tolerance, capability of a functional unit to continue
the execution of the demanded function when faults or deviations
exist.
MooN (M out of
N) architecture
The architecture describes the specific configuration of hardware
and software in a system. N is the number of parallel channels and
M defines how many channels must be working correctly.
MRT Mean Repair Time
MTTR Mean Time To Repair
PFD
avg
Average probability of a dangerous failure on demand of the safety
function
1. General information