SMAR LD400 Operation And Maintenance Instruction Manual page 6

LD400 - Operation and Maintenance Instruction Manual
Acronyms and Abbreviations
Acronym /
Abbreviation
HFT
MTBF
MTTR
PFD
PFDAVG
SIL
SFF
Low Demand Mode
DTM
LRV
URV
Multidrop
IV
Designation
Hardware Fault Tolerance
Mean Time Between Failures
Mean Time To Repair
Probability of Failure on Demand
Average Probability of Failure
Safety Integrity Level
Safe Failure Fraction
Low Demand Mode of Operation
Device Type Manager
Device Configuration
Device Configuration
Multdrop Mode
Description
The hardware fault tolerance of the device.
This is the capability of a functional unit to continue the execution
of the demanded function in case of faults or deviations.
This is the mean time period between two failures.
This is the mean time period between the occurrence of a failure
in a device or system and its repair.
This is the likelihood of dangerous safety function failures
occurring on demand.
This is the average likelihood of dangerous safety function
failures occurring on demand.
The International Standard IEC 61508 specifies four discrete
safety integrity levels (SIL 1 to SIL 4). Each level corresponds to
a specific probability range regarding the failure of a safety
function. The higher the safety integrity level of the safety-related
systems, the lower likelihood of non-execution of the demanded
safety functions.
The fraction of non-hazardous failures, e.g. the fraction of failures
without the potential to set the safety-related system to a
dangerous undetected state.
Measuring mode with low demand rate, in which the demand rate
for the safety-related system is not more than once a year and is
not greater than double the frequency of the periodic test.
The DTM is a software module
accessing device parameters, configuring and operating the
devices and diagnosing problems. By itself, a DTM is not
executable software.
Lower Range Value of the measurement range.
Upper Range Value of the measurement range.
In multidrop mode, up to 15 field devices are connected in
parallel to a single wire pair. The analog current signal serves just
to energize the two-wire devices providing a fixed current of 4
mA.
which provides functions for