Siemens SIPART PS2 PA 6DR55 Series Operating Instructions Manual page 284

Glossary
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)
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)
SIMATIC software
Program for process automation (e.g. PCS7, WinCC, WinAC, PDM).
Zero point shutdown
The zero point shutdown guarantees a tight closing of the valve if an input signal is < 2% of
the maximum value. The coil current is then set to zero. The zero point shutdown must
normally be deactivated to set the minimum coil current
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 potentially explosive gaseous atmospheres normally never build up or build up
for a short while during the normal operation of a device.
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SIPART PS2 with PROFIBUS communication
Operating Instructions, 09/2007, A5E00127926-07
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AVG