The buoy returned to power at UTC 16:00 (local noon) on March 31st. Neither datalogger had logged any records since the buoy lost power on December 30th, suggesting that the buoy had experienced a complete loss of power to all of its sensors and dataloggers.
Judging from the compass data, the buoy was not at its deployment site when it powered up, but was towed to that site the following day. Based on these data I count its deployment dataset as beginning at UTC 15:00 (11am local) on April 1st, 2016.
Battery voltages were steady both before and after these outages, suggesting that the battery had never been disengaged from the solar panels and the charging systems. This is identical to what was observed at the South Water Caye buoy (November 2015, to be described in a maintenance log post still to come), where the problem was traced to the solar regulator, also known as the "automatic sequencing charger" or ASC. The ASC used at all CREWS buoys to date has a "low voltage disconnect" or LVD feature which cuts power to the system load if it determines that the power supply falls below a certain level, on the theory that continued operation at low voltages may be more damaging to the electronics than an outright power loss. This LVD is said to be designed to kick in at about 11.5V.
Similar problems with the ASC have been known to occur at the Buccoo Reef buoy, where systems were rewired to bypass the LVD protection, and have also factored into some power problems experience by the Little Cayman buoy. Counting CWDR1, BUTO1, SWBZ1 and CCMI2, the ASC may be implicated in power losses experienced at as many as four of the network's eight buoys.
Note that as of this writing I have no direct knowledge of any intervention that may have taken place, either by local DR personnel or by YSI support people. My speculation about the buoy's recovery from its deployment site, an intervention that may or may not have involved the ASC, and the buoy's subsequent redeployment, is just that: speculation.
Based on my examination of the last four months of data some further observations can be made:
- Buoy performance is generally good: redundant measurements of barometric pressure, air temperature, humidity and wind speeds all show excellent agreement. I have begun work on a feed of this buoy's meteorological data from AOML/CHAMP systems to NDBC.
- Diagnostics suggest that the 'Main' Junction box is growing unacceptably moist. Humidity levels range diurnally between 45% and 65%. I have previously suggested that 20% humidity would be a reasonable target and that anything exceeding 50% should be considered excessive. The other diagnostic humidity metric (that from the 'Met' junction box) remains well under 20%.
- The two wind sensors report directions that are consistently offset from one another by 7° to 14°, suggesting that they may not be correctly aligned with one another or with the station compass. A realignment should be attempted during the next maintenance operation, while taking care to note which sensor(s) have been adjusted and by how much. At a wild guess I might trust the RMYoung anemometer directions more, based solely on suggestions at other buoys that the WXT base is not always solidly mounted in place.
- The EXO's CT2 sensor is doing okay with sea temperatures but its salinity reports appear to be unbelievably low, starting from about one month after redeployment. This may simply be an issue with insufficiently frequent calibrations (the CT2 is said to require in-field recalibrations every 1-2 months), or it could indicate CT2 fouling or failure. There is no suggestion in the data record that the EXO has been calibrated since the buoy returned to power.
- EXO battery voltages were initially steady at 6V but start dropping lower on about June 13th. It is not known whether this suggests any kind of problem with the EXO or casts any doubt on the accuracy of its sensors.