●
Safe STOP function: Safe STOP
-
An operation command of standard controls (in directions OPEN or CLOSE)
will only be executed if an additional enable signal for the operation com-
mand is applied.
-
If this is not the case, operation in directions OPEN or CLOSE is stopped
or even suspended (motor is switched off).
-
The Safe STOP function is effective for all operation commands of the
standard actuator controls, irrespective of the command source (e.g. Re-
mote or Local).
●
Safe ESD function combined with Safe STOP function
-
Safe ESD function has a higher priority i.e. if both functions are activated,
the actuator is operated into the configured direction (OPEN/CLOSE).
Information
The safety functions of the AC .2-SIL / ACEXC .2-SIL are always controlled via
24 V DC.
“Safe end position feedback” is not part of the certification by TÜV Nord and neither
part of this safety manual. Please refer to the specific safety manual for details
regarding this function.
The different configuration options of the safety functions are described in the
<Configuration (setting)/version> chapter.
4.3.
Safe inputs and outputs
Safe inputs for Safe OPENING/CLOSING (Safe ESD function):
●
Safe ESDa
●
Safe ESDb
Safe inputs for safe stop (Safe STOP function):
●
Safe STOP OPEN
●
Safe STOP CLOSE
Safe outputs (indication that it might not be possible to perform the safety function:
●
SIL fault
●
SIL ready
For detailed information on safe inputs and outputs, refer to <Configuration
(setting)/version> chapter and <Installation> chapter.
4.4.
Redundant system architecture
Besides the already described typical safety instrumented system including an
actuator, safety can be increased by implementing a second, redundant valve and
actuator with actuator controls in SIL version into the safety instrumented system.
The decision on the appropriate version depends on the entire system.
Information
Depending on the safety function and the safety instrumented task of this safety
function, it must be verified for each and every application whether and - if so - in
which configuration a HFT>0 can be actually achieved when using several actuators.
This applies in particular – but is not limited to – the Safe STOP safety function.
A possible example for Safe CLOSING or Safe OPENING is shown in figure 3 and
4. Another example, in which several actuators do NOT achieve redundancy, is a
Safe STOP function used to safely exclude the movement of mechanical system
parts, if, for example, the fire brigade has to access the plant section in question in
case of an emergency. For this application, use of two actuators does generally not
result in a 1oo2 but in a 2oo2 system in terms of safety effect to be achieved.
Therefore, the HFT is not increased in this case.
14
Part-turn actuators
Safety instrumented systems and safety functions
with AC 01.2-SIL/ACExC 01.2-SIL
