Furlong, M.E. and Brito, M.P.
Reliability Case Notes No. 4: Autosub6000 and Autosub3 actuator potentiometer failure analysis and testing report. Southampton, UK, National Oceanography Centre Southampton, 30pp.
(National Oceanography Centre Southampton Research and Consultancy Report, (58) ).
During the James Cook Cruise 27 Autosub6000 aborted mission 12 due to a failure in the
position feedback potentiometer of the stern plane actuator. The same actuator is used on
Autosub3 which is heading to the Pine Island glacier in Antarctica in January 2009. A
similar failure of the Autosub3 actuator while under the ice would result in the loss of the
This report initially describes the investigation into the failure of the feedback
potentiometer and shows that the potentiometer’s conductive plastic track became detached
from its ceramic substrate and broke up. The report then describes the testing performed to
evaluate the reliability of the potentiometer. This involved an accelerated aging test to
simulate the worst case conditions seen by the potentiometer in the actuator. This was
achieved by oscillating the potentiometer at 4Hz to simulate the actuator movements whilst
cycling the pressure of the Morlina 10 oil surrounding the potentiometers.
During the testing the 10kΩ potentiometers used in the actuator were not available, and so
5kΩ potentiometers from the same range were tested as a substitute. It was assumed that
these 5kΩ potentiometers would produce similar results, however it was found during the
testing that the formulation of the 5kΩ potentiometer track was different from the 10kΩ;
whether this affects the reliability is not known.
Due to the large amount of time required to perform each test only 16 5kΩ potentiometers
were tested. Although no failures occurred, the sample was too small to give a high
statistical confidence that the potentiometers would survive the cruise. To further reduce
the risk four 5kΩ potentiometers that were to be used on Autosub3 were tested for
approximately 72 hours in a ‘burnt in’ process. As an early failure similar to that of
Autosub6000 potentiometer would have been detected during this process, the chance of
the potentiometers failing was significantly reduced. Thus the burnt in potentiometers were
considered acceptable for use on Autosub 3 during the Pine Island campaign.
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