Siemens SIPART PS2 Operating Instructions Manual page 323

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. PCS 7, WinCC, WinAC, PDM, STEP 7).
Zone 0
Area in which potentially explosive atmospheres build up often, regularly or over long durations
during the normal operation of a device.
Zone 1
Area in which potentially explosive atmospheres build up occasionally during the normal
operation of a device.
Zone 2
Area in which a potentially explosive atmosphere normally never builds up or builds up only
for a short while during the normal operation of a device.
SIPART PS2 with PROFIBUS PA
Operating Instructions, 02/2016, A5E00127926-AB
Glossary
323