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Tests and maintenance
8.3.
Actuator monitoring for safe end position feedback" safety function
Information
8.4.
Proof test (verification of safe actuator function)
Information
28
Performing a PVST includes diagnostics of the safety-related components. This
ensures improved safety figures compared to applications without or with minor
diagnostics.
To ensure proper function of the "safe end position feedback", the signalling behaviour
of the actuator must be checked at regular intervals. This can either be performed
within the framework of an actuator operation occurring during standard operation
(reaction monitoring) or within the framework of a scheduled PVST.
PVST is used to test the function of actuator controls and actuator not operated on
a regular basis and can therefore not use reaction monitoring for diagnostics.
The diagnostics by means of the PVST should be performed at least 10-times more
often than the proof test and also at least ten times more often than the demand rate
of the safety function.
Monitoring and assessment of PVST or reaction monitoring must be ensured by the
logic unit of the safety instrumented system:
Actuator movement can be requested via any input.
The SIL failure of the SIL module has to be assessed during the entire test
procedure. If a fault is signalled, the test is considered as failed
Assessment whether the safe end position feedback function signals as desired
has to be performed at the end position switches wired directly to the customer
connection.
The actuator must be in one of the following positions:
-
In one of both end positions prior to starting the test run. The test run is
performed out of the end position and back to this end position.
-
At a sufficient distance from both end positions prior to starting the test
run. The test run is performed into an end position and out of this end po-
sition.
In both cases, the travel distance must be sufficient to allow for full tripping of
the end position switch. It must be checked whether the end position switch
signals the expected position both at the beginning, during and at the end of
the test.
Test run monitoring must be dynamic. This means a dynamic test whether the
signal change corresponds to the expected value.
If PVST is performed out of or into one of both end positions, only the contact of this
end position is checked for correct operation. If both end position switches
(OPEN/CLOSE) are safety relevant, a full stroke test can be performed, for example.
The proof test serves the purpose to verify the safety-related functions of the actuator
and actuator controls.
Proof tests shall reveal dangerous failures which might remain undetected until a
safety function is started and consequently result in a potential danger.
During execution of the proof test, the safety function is unavailable for a short time.
Depending on both version and configuration, the proof test includes the
following tests:
1.
Check Safe ESD safety operation (Safe OPENING/CLOSING)
2.
Check SIL fault signal "Actuator monitoring".
3.
Check Safe ESD reaction for "Motor protection (thermal fault)" signals.
4.
Check Safe ESD reaction to "Limit seating with overload protection" (limit and/or
torque evaluation).
5.
Check Safe ESD reaction to "Forced limit seating in end position" (limit evalu-
ation)
for actuators with electromechanical control unit.
6.
Check Safe ESD reaction to "Forced limit seating in end position" (limit evalu-
ation)
for actuators with electronic control unit and limit switches.
SA .1 with AC 01.2-22X/-22Y/ACExC 01.2-22X/-22Y
Multi-turn actuators
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