Field of Application
4
TTH200, TTR200, TTH300, TTF300, TTF350 SM/TTX200/TTX300/SIL-EN
1 Field of Application
Temperature monitoring of solids, fluids and gases of all types in containers and pipes
according to the special safety engineering requirements of IEC 61508.
The operating limits are defined in the data sheets and operating instructions for the separate
models. In case of questions, please contact your ABB partner.
2 Acronyms and abbreviations
Acronym /
Abbrevia-
tion
English
Description
HFT Hardware
Fault
Tolerance
Hardware error tolerance of the unit.
Ability of a functional unit (hardware) to continue to
perform a required function when faults or errors are
prevailing.
MTBF Mean
Time
Between Failures
Mean Time Between Failures
MTTR
Mean Time To
Repair
Mean time between the occurrence of an error in a unit
or system and its repair.
PFD Probability
of
Failure on Demand
Probability of hazardous failures for a safety function on
demand
PFD
AVG
Average
Probability
of Failure on
Demand
Average probability of hazardous failures for a safety
function on demand
λ
D
Dangerous
Rate of hazardous failures (per hour) affecting a channel
of a subsystem, corresponds to 0.5
λ
(assuming 50%
hazardous failures and 50% non-hazardous failures)
λ
DD
Dangerous
Detected
Rate of detected hazardous failures (per hour) affecting
a channel of a subsystem. (This is the total rate of
hazardous failures within one channel of a subsystem.)
λ
DU
Dangerous
Undetected
Rate of undetected hazardous failures (per hour)
affecting a channel of a subsystem. (This is the total rate
of undetected hazardous failures within a subsystem.)
λ
SD
Safe Detected
Rate of detected non-hazardous failures (per hour)
affecting a channel of a subsystem. (This is the total rate
of detected non-hazardous failures within one channel of
a subsystem.)
λ
SU
Safe Undetected
Rate of undetected non-hazardous failures (per hour)
affecting a channel of a subsystem. (This is the total rate
of undetected non-hazardous failures within one channel
of a subsystem.)
