Specifications

15
3 Trouble Shooting
So far faultless buoy behaviour with regular maintenance only has been assumed. This chapter
will deal with minor problems that may be traced and solved by you yourselves. The easiest
way to diagnose buoy problems is to query the onboard microcomputer. It will help you to
identify the problem and check if the electronics unit works fine. Still the real problem may lay
further down or up with the electronics module of the malfunctioning sensor or communication
means. Therefore, the next step is to carry out some checks on the respective module as
suggested. If all else fails the buoy must be returned to Datawell Service.
3.1 Buoy diagnosis
The easiest way of fault finding is to plug into the buoy microprocessor directly. Leave the main
hatchcover connector string connected, apply external power to the electronics unit and connect
a serial cable to your terminal. Send the status command and check the buoy response for
any irregularities. Furthermore, you should inspect the human-readable HISTORY.DOC file on
the logger flash card for clues, especially at the end, see subsection 5.12.7.
If no problems are found, the buoy must be switched on while running in debug or
verbose mode. In this mode the microprocessor will output a wider range of event messages to
your terminal. If still no problems are found, you can switch to RXD-emulation mode to verify
the overall healthiness of the motion sensors. Please refer to subsections 5.11.4-6.
3.2 Batteries
A general cause for apparent buoy failure is when the batteries are flat. If the buoy internal
processor, sensors or communication means do not get enough power their behaviour can be
unpredictable. Before commencing detailed tests of the supposedly malfunctioning buoy part
reassure yourself that the batteries are not exhausted. To this end all buoys are fitted with a test
box. At the test box each series of battery cells can be measured with a voltmeter independently.
If all series are exhausted replace the batteries or apply external power for further checks, see
section 5.10.
3.3 WR-SG and DWR-MkIII motion sensors
The stabilized platform motion sensor is a very delicate instrument that can only be repaired by
skilled persons. In this section the symptoms of malfunction will be described, but faults are
almost impossible to repair for a layman.
3.3.1 Stabilized platform and accelerometer
Under normal circumstances the wave record should have a steady average position. A
pronounced peak of the spectral density at the low frequency side of the spectrum raises the
suspicion that the stabilized platform suspension is out of order. Persistent peaks that are orders
of magnitude higher than 10
−2
m
2
/Hz in the frequency range (0.025-0.035 Hz), corresponding to
1 cm noise, are suspect. Furthermore, in case of a DWR-MkIII the inclination angle, output in
response to a status request, should correspond to the local inclination angle of the earth
magnetic field.
If the mean vertical keeps changing all the time, there may be several causes. An
additional long period oscillation (30-40 s) reveals that the platform, on which the
accelerometer sits, slightly swings horizontally. Likely causes are turbulence in the fluid or a
sudden temperature change, such as occur after launching. Too fast rotations of the Waverider
may also cause turbulence. These disturbances will disappear within 24 hours.
If the variation in the mean vertical is rather erratic this may be caused by damaged
suspension wires, moisture on the electronics, bad contact in the accelerometer or low battery
voltage. A large or varying offset of the vertical accelerometer in the system file, subsection
5.7.3, usually indicates a problem related to intermitting contacts.