WIKA DELTA-comb DPGS40TA Manual De Instrucciones página 8

2. Safety
2.3.4 Abbreviations
Abbreviation
λ + λ
EN
S
D
λ
DD
λ
DU
Operating mode
with low demand
rate
Operating mode
with high demand
rate
DC
HFT
SIL
8
Description
λ safe + λ dangerous
S
D
Sum of all mean failure rates for the system. A safe failure occurs
if, during this, the measuring system remains in a functioning state
or the failure detection is signalled by an alarm. A failure to danger
occurs if the measuring system, through this, can switch into a dan-
gerous or functionally inoperable condition.
λ dangerous detected
DD
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.
λ dangerous undetected
DU
With undetected failures to danger, the failure is not detected
through diagnostic tests.
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.
In this operating mode, the safety function of the safety system is
only carried out on request. The frequency of the request is more
than once a year.
Diagnostic coverage
Percentage of failures to danger that are detected by automatic
diagnostic online tests.
Hardware fault tolerance
Capability of a functional unit to continue the execution of the de-
manded function when faults or deviations exist.
Safety integrity level
The international standard IEC 61508 defines four discrete safety
integrity levels (SIL 1 to SIL 4). Each level corresponds to a range of
probability with which a safety-related system performs the specified
safety functions in accordance with the requirements. The higher
the safety integrity level of the safety-related system, the greater the
probability that the safety function is executed.
WIKA operating instructions DPGS40TA with component testing