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Glossary
Safety function
Defined function executed by a safety-instrumented system with the objective of attaining or
maintaining a safe status of the system by taking a defined hazardous incident into account.
Example: limit pressure monitoring
Safety-instrumented system
A safety-instrumented system (SIS) executes safety functions that are required to attain or
maintain the safe status in a system. It consists of sensors, logic unit/control system and final
controlling elements.
Example: a safety-instrumented system consists of a pressure transmitter, a limit signal
indicator and a servo valve.
Sensor
Converter that converts mechanical or other non-electric variables into electric signals.
SIL
The international standard IEC 61508 defines four discrete safety integrity levels (SIL) from
SIL 1 to SIL 4. Every level indicates a probability range for the failure of the safety function.
The higher the SIL of the safety-instrumented system, the higher the probability that the
required safety function works. The achievable SIL is determined by the following safety-
instrumented characteristics:
● Average probability of dangerous failures of a safety function on demand (PFDAVG)
● Hardware fault tolerance (HFT)
● Safe failure fraction (SFF)
SIMATIC software
Programs for process automation (e.g. PCS7, WinCC, WinAC, PDM, Step7).
Zone 0
Area in which hazardous potentially explosive gaseous atmospheres build up often, regularly
or over long durations during the normal operation of a device.
Zone 1
Area in which potentially explosive gaseous atmospheres build up occasionally during the
normal operation of a device.
Zone 2
Area in which a potentially explosive gaseous atmosphere normally never builds up or builds
up only for a short while during normal operation of a device.
288
SIPART PS2 with and without HART
Operating Instructions, 09/2014, A5E00074631-12
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