Siemens SITRANS TH400 Operating Instructions Manual page 59

Sensor
In electrical engineering, a sensor is a component that can qualitatively measure not only
specific physical or chemical properties (such as heat radiation, temperature, humidity,
pressure, excess pressure, sound, brightness, magnetism, acceleration, force) as well as the
physical condition of its surroundings or register them as quantitatively measured variables.
SIF
A part/function of a safety-instrumented system that reduces the risk of a dangerous failure
occurring.
SIL
The international standard IEC 61508 defines four discrete Safety Integrity Levels (SIL) from
SIL 1 to SIL 4. Each level corresponds to the probability range for the failure of a safety
function. The higher the SIL of the safety-instrumented system, the higher probability that the
required safety function will work.
The achievable SIL is determined by the following safety characteristics:
● Average probability of dangerous failure of a safety function in case of demand (PFD
● Hardware fault tolerance (HFT)
● Safe failure fractions (SFF)
USB
The Universal Serial Bus (USB) is a serial bus system for connecting a PC/laptop to external
devices such as: modems.
SITRANS TH400
Operating Instructions, 06/2010, A5E01018688-02
Glossary
)
AVG
59