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8.5
Safety characteristics
The safety characteristics necessary for use of the system are listed in the SIL declaration of
conformity. These values apply under the following conditions:
● The positioner is only used in applications with low demand rate for the "Low demand
mode".
● The positioner is blocked against unwanted and unauthorized changes/operation.
● The signal source with 0 mA or the power supply source with 0 V for the SIPART PS2
positioner is generated by a safe system that fulfills SIL 2 for single-channel operation.
● The connected single-acting type actuator returns the valve to the safe end position by
spring force in the following scenarios:
– With a chamber pressure (Y1 connection) up to a third of the maximum available
● The air outlet does not contain any additional cross-sectional contractions leading to an
increased dynamic pressure. In particular, a silencer is only allowed if icing or other
contamination is ruled out.
● The restrictor in the Y1 circuit may not be completely closed during operation.
● The auxiliary pneumatic power is free of oil, water and dirt in line with:
DIN/ISO 8573-1, maximum class 2
● The average temperature viewed over a long period is 40 °C.
● Fault rates are calculated on the basis of a mean time to repair (MTTR) of 8 hours.
● In case of a fault, the pneumatic outlet of the positioner is depressurized. A spring in the
pneumatic actuator must move the valve to the pre-defined, safe end position.
● A dangerous failure of the positioner is a failure whereby the pressure outlet is not
depressurized or the safety position is not reached when the signal source is 0 mA or the
power supply source is 0 V.
See also
Settings (Page 142)
SIPART PS2 with and without HART
Operating Instructions, 09/2014, A5E00074631-12
supply air pressure (PZ connection)
Functional safety
8.5 Safety characteristics
143
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