Honeywell FlexLine SmartServo 954, Service Manual

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OPERATION
250 Service Manual Part No.: 4417340 Revision 1
954 SmartServo FlexLine
8.7 Servo Auto Test
The Servo Auto Test (SAT hereafter) is an automatic safety related
function meant to reduce the small risk of tank overfill or underfill
caused by a failing servo gauge. Immediate after the gauge detects that
tank loading has finished a SAT is executed to rule out (or detect) that
the gauge is unable to measure the product level due to some failure
(e.g. blockage of displacer). The gauge will raise or lower the displacer
over a programmable distance and will perform some checks. If the
movement is not completed within the expected time or one of the other
checks fail, the gauge will retry. If this second try also fails, a third and
final attempt is made. Should even the third try fail, the gauge will
update the display by removing the measurement unit and display the
fail mode. After that the gauge will go into General Fail mode and the
PV status code will show one of the SAT failures, e.g.
‘SAT displacer stuck’ (SmartView codes 6172-6180). From this moment
on the gauge will respond only to status requests and the reset
command.
The SAT will not only be executed immediately after tank loading has
apparently stopped, but also at regular configurable intervals.
If the 954 SmartServo FlexLine is used for overfill or underfill protection,
the SAT must be enabled (refer to ‘954 SmartServo FlexLine Safety
Manual’).
The SAT can also be performed manually by entering one of the
commands ‘SAT upwards’ or ‘SAT downwards’.
Entity name Entity name
(SmartView) Description
[SAT upwards] [SAT upwards]
(Displ. level)
Performs a SAT upwards. The displacer is raised
above the liquid level, the displacer weight and the
hysteresis of the system is measured and checked
against certain limits.
[SAT downwards]
[SAT downwards]
(Displ. level)
Performs a SAT downwards. The displacer is
immersed in the liquid level and the displacer weight in
liquid is measured and checked against certain limits.