11
Table 8: Overview self-locking for AUMA actuators (at the time of printing of this document)
If actuators with insufficient self-locking function paired with “Forced torque seating in end
position” SIL seating type are used for the safety function, the following effect might occur:
During ESD, the actuator operates to the end position and switches off due to reaching
the travel position and the tripping torque. Thereafter, the gear train is relieved and the
torque falls below the preset limit value. As a matter of fact, the actuator controls detect
this incident and switch the actuator on again since the behavior is correctly considered
as termination of the ESD condition. The latter generates additional torque until the
switching off condition is reached again, and so on. The “pumping effect” of the actuator is
the consequence.
To successfully avoid this incident, we recommend either selecting actuator or other
elements with sufficient self-locking within the gear train or – if acceptable from a process and
safety point of view – selecting “Forced limit seating in end position” as safety function.
3.4 Operation mode (low/high demand mode)
The safety functions of the actuators supplied by AUMA are suitable for the low demand
mode and may only be used in this operation mode. If a non-safety instrumented function of
basic process control system is executed via the same actuator in addition to the safety
function, note that while considering the sum of non-safety instrumented function, required
1)
tests and safety function, the defined number of maximum permissible cycles for the
2)
respective actuator as well as the maximum number of starts may not be exceeded during
deployment of the actuator within a safety instrumented system.
3.5 Further notes and indications on architecture
HFT is 0.
The systematic capability is 3 (SC=3)
Only flanges of sizes or larger may be used for valve attachment.F07 or FA07
If the actuator is equipped with a position transmitter like MWG, RWG or EWG, they may not
be integrated within the safety instrumented system.
The actuator safety functions can be considered as type A device.
The operating time for a complete stroke must exceed 4 seconds. Attention: Any modification
of the nominal stroke results in operating time change.
Safety function(s) and their feedback signals may only be issued via the digital inputs and
outputs of the SIL module.
The signal issued via SIL fault output must be permanently evaluated. If the output
signals a fault, assumption can be made that the safety function is not available. The safety
function must be checked without delay. Possibly further safety measures are to be taken
until the safety function is restored without fault.
3.6 Applications (environmental conditions)
When specifying and using the actuators within safety instrumented systems, make sure that
the permissible service conditions and the EMC requirements by the peripheral devices are
met. Service conditions are indicated in the technical data sheets:
1) Definition of “cycles” according to EN 15714-2:2010
2) Definition of “starts” according to DIN EN 15714-2:2010
Multi-turn actuators
SA series with Control 3.XX /NI/SIL
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