Voltage trends at Little Cayman, 2013-present

This post is expected to be the last of a series of posts to share the results of my recent evaluation of data produced by all of the CREWS/CCCCC buoys over their lifetimes, from 2013 to the present.  This post will briefly discuss the curious downward trend over time in voltage minima that is common to all three operational buoys.

This trend was first remarked upon in an email conversation between myself and Matt Previte of YSI on January 7th and 8th, 2015.  We had had occasion to examine the voltage levels at the Little Cayman (CCMI2) buoy because on December 29th, 2014 it had suffered a complete loss of power.  Subsequent to discovering that power failure I posted an analysis of 2014 voltage levels for CCMI2 with particular attention to the final month of data.  In this post I remarked:

Note the unexplained, slow downward trend of low voltages throughout the year.  This is not obviously related to the final loss of power but it is still curious.

Matt's email to me on January 7th touched upon that subject very briefly:

I'm also surprised by the gradual, overall decline in min/max of the daily battery voltage. I'll ask around to see if anyone else has thoughts on that. It wasn't below operational levels and batteries due wear, but seemed a little odd.

My own January 8th reply to this remark included the following:

I'm pretty sure I've seen similar patterns at (some of?) the other buoys, but I will have to let you know next week if I can back up that statement with real data. [...] I agree that the gradual low-voltages decline is mildly worrying without being hugely alarming.

In fact I did not follow up on this subject as promised until now, since I've just spent several weeks looking at trends in all of the CREWS/CCCCC data, and indeed the gradually-declining trend of voltage minima appears in the data from all three operational buoys.

For this post, we examine the voltage trends at Little Cayman, Cayman Islands (CCMI2).  Voltages are sampled every five seconds and then at 10-minute intervals the minimum voltage from the last ten minutes is reported.  This graph shows voltage minima reported by the Met datalogger (green) and the Main datalogger (red) as well as their difference (in blue, equal to Met - Main).  The first two parameters are graphed on the left axis and the third on the right, with both axes sharing the same scale but offset from one another by 11V.

Please click on this image to see it in larger form.

The most notable features of this graph are as follows: an obvious dip in voltage from October 14th - 29th while the station was on land for maintenance; a loss of data during the period from December 29th, 2014 until March 12th, 2015, caused by the station's power loss and subsequent redeployment; and an unexplained voltage dip at the end of the dataset beginning June 1st, 2015.  Data for this analysis were last refreshed on June 9th, 2015.

At this station the Met voltages were slightly lower than the Main voltages (by 0.057V on average) so my subsequent analysis of battery minima focuses on the Met voltages.

My informal analysis looked for the 'lower edges' of the minima to try to quantify how much they were decreasing over time and how quickly.  This is a largely subjective evaluation.  For CCMI2, this 'lower edge' was about 12.79V at deployment time.  This edge crept lower still by about 0.1V every 3-6 months until the power failure on December 29th, 2014, at which point (apart from obvious power irregularities) I estimate this lower edge to have been at about 12.52V, for a loss of about 0.33V overall.  Following redeployment this trend appears to have reversed itself somewhat, with a lower edge at about 12.60V for a short-term gain of about 0.08V.

Similar analyses were carried out for this buoy's sister stations at Buccoo Reef, Tobago (BUTO1) and at Speyside / Angel's Reef, Tobago (ARTO1).  Two of the stations (BUTO1, ARTO1) reported lower Main voltages on average and one (CCMI2) reported lower Met voltages.  All three stations exhibited a gradual downward trend in voltage minima, losing on average 0.1V every 4-8 months, with some slight changes in pace noted (decelerating at BUTO1, accelerating at ARTO1, constant at CCMI2).  There was also one reversal of this trend noted at CCMI2 following that station's power loss and redeployment in early 2015.

The complete analyses for the other voltage minima, including graphs, may be found at this link for BUTO1 and at this link for ARTO1.

(signed)
Mike Jankulak

Junction Box Humidities at Little Cayman, 2013-present

This post is part of a series of posts to share the results of my recent evaluation of data produced by all of the CREWS/CCCCC buoys over their lifetimes, from 2013 to the present.  This post will discuss the diagnostic relative humidity (RH) data collected from inside two of the buoy's junction boxes: the 'Main' and 'Met' junction boxes which house the Main and Met dataloggers, respectively.  Overly high humidities within either of these junction boxes could lead to a failure of the buoy's controlling electronics and lengthy interruptions in the data stream.

By way of example please see this post from the Little Cayman station log (including photos), which concludes that a "catastrophic power loss" was caused by "condensation" within the "solar panel junction box."  To my knowledge there are no diagnostic RH sensors deployed in the solar panel junction boxes at any CREWS/CCCCC station but this serves as an important lesson about the damage that moisture incursion can have on station operations.  In this case the Cayman station was nonoperational for 73 days and when redeployed it was found that communications with the WXT (Vaisala's 'Weather Transmitter') had failed, which may indicate another yet-undiagnosed effect of junction box condensation at that buoy.

The following graph shows the Little Cayman (CCMI2) diagnostic RH values plotted over the buoy's deployment lifetime to date (through June 9th, 2015).  The red line is RH maxima as measured within the Main junction box and the green line is RH maxima as measured within the Met junction box.

Please click on this image to see it in larger form.

Some obvious features of the above graph are as follows: initial buoy deployment was on October 23rd, 2013; the Main RH levels (red) ceased to fall below 20% on November 16th, 2013; there is a nine-month period when Main RH levels (red) remain strictly above 60% (January 17th - October 27th, 2014); there is a break in data lasting from the station's power failure (December 29th, 2014) until redeployment (March 12th, 2015); and there is a two-week period (April 30th - May 14th, 2015) during which there were no Met RH updates (green) because the Met logger's program stopped running (a situation believed to have been caused by excessive watchdog errors, indicating a potential programming/timing problem).  Note that the station's annual maintenance operations took place October 14th - 29th, 2014, throughout which RH data continued to be collected.

Note that these data report only the maximum RH seen in a ten-minute period of those raw values collected every five seconds.

A natural question is how humid is too humid?  I have heard it suggested that these junction box humidity maxima should not exceed 20%, and the lifetime of Met junction box RH data from the Buccoo Reef, Tobago CREWS/CCCCC buoy shows that this is an entirely attainable goal and can be regarded as a reasonable target.  However, at what point should overly-high RH values prompt remedial intervention?  I have for many years run CREWS programming tests inside my office which has had the side-effect of collecting a long-term dataset of indoor RH values, in an environment that is dry enough to prevent any damage from moisture or condensation.  Based on these somewhat accidental datasets I would suggest that RH values up to 50% may be considered tolerable, but that prolonged measurements of diagnostic humidity in excess of 50% should be considered cause for immediate reparative action.

The story told by these data, then, is twofold:  the Met junction box (green line) begins nicely stable and largely below 10% for about six months, a pattern which starts to be disrupted on April 10th, 2014.  On June 6th, 2014 the pattern shifts significantly above 10% for the first time, and this increasing pattern becomes quite obvious on August 7th, 2014, which is the last Met RH report to fall below 10%.  This only becomes worrisome on October 29th, 2014, the date of buoy redeployment after its annual maintenance operations, which also happens to be the Met RH's last report to fall below the 20% humidity threshold.  Met RH values remain in the worrisome-but-not-alarming range (above 20% but below 50%) from October of 2014 to May of 2015, but following the two-week period of non-updates of Met RH data (i.e. beginning May 14th, 2015, see above) Met RH values are well into the >50% alarming range, with 97.2% of Met RH reports rising above 50% humidity.  In the final 6 days of data examined in this report, in fact, all of the Met RH reports are above 90% humidity.

The Main RH numbers for this station are even more concerning.  These numbers started low but spiked quickly.  Less than one month after initial deployment the Main RH numbers rose above 20% and never recovered, beginning November 16th, 2013.  Two months after that, on January 17th, 2014, the Main RH numbers rose above 60% humidity and remained there until the buoy's annual maintenance operations nine months later in October.  Following those operations Main RH levels dropped slightly but remained at >50% humidity for 97.2% of the time.

These diagnostics indicate that there are presently serious humidity problems in both of the Main and Met junction boxes at this site, with the Main junction box problems being pretty much constant over the lifetime of the buoy to date and the Met junction box problems starting slow but becoming very serious over the last few months.  Given that this is the site where junction box condensation was blamed for a very serious power failure, both of these humidity concerns should be attended to at the earliest possible opportunity.

Similar analyses have been conducted at this station's sister buoys located at Buccoo Reef, Tobago (BUTO1) and at Speyside / Angel's Reef, Tobago (ARTO1).  A pattern that is common to all three of these buoys is that the Main RH levels are all presently at alarming levels, after starting out acceptably low during initial deployment and increasing much more quickly than the Met RH levels do.  This might suggest a design or construction problem with the moisture seals on the Main junction box, or a lack of clear deployment instructions regarding proper sealing of the junction boxes and the use of fresh desiccant.

The Met RH patterns at the three buoys range from BUTO1, where Met RH levels start low and stay low throughout the buoy's entire lifetime, to ARTO1, showing a mildly-increasing trend of Met RH levels that is not yet any cause for alarm, to CCMI2, where Met RH levels began low but increased quickly and are presently at levels that are alarmingly high.  There does not seem to be any reason to suspect a systemic problem with the Met junction box design, construction, or deployment practices as there is in the case of the Main junction boxes.

The complete analyses for the other RH diagnostics, including graphs, may be found at this link for BUTO1 and at this link for ARTO1.

(signed)
Mike Jankulak

WDirDiff/Compass data from Little Cayman, 2013-present

This post is part of a series of posts to share the results of my recent evaluation of data produced by all of the CREWS/CCCCC buoys over their lifetimes, from 2013 to the present.  This post will discuss the offsets (WDirDiffs) between the wind directions reported by the analog anemometer manufactured by RM Young (RMY) and the sonic wind sensors on Vaisala's Weather Transmitter (WXT).  Ideally these offsets should be less than 5° in absolute value.  This post will further discuss the raw directions reported by the buoy's Compass.

For reference, some important milestones in this station's lifetime are as follows:

• 10/23/2013: initial deployment
• 10/14/2014 - 10/29/2014: buoy brought to land for a maintenance operation
• 12/29/2014 - 3/12/2015: station offline due to a power failure, brought to land before redeployment
• 3/12/2015 - 6/9/2015 (present): station's WXT non-operational (no redundant wind data)

The following graph shows the differences in wind directions reported by the two wind sensors (red, on the left axis) and the raw directions reported by the compass (blue, on the right axis).  All directions are reported in degrees of compass but note where the scales are different by a factor of 6x and the zeroes offset, with the WDirDiff axis running on the left from -30° to +30° but the Compass axis running on the right from 0° to 360°.  A negative WDirDiff would indicate that the reported WXT wind directions are lower than the corresponding analog anemometer values.

Please click on this image to see it in larger form.

First of all the Compass averages suggest that this buoy has been deployed in the same orientation throughout its entire lifetime to date.  See the report of WDirDiff/Compass averages for the Buccoo Reef station for an example where this does not appear to be the case.

The second thing to note from this graph is that the WDirDiffs average through the end of 2014 (after which time WXT wind directions are not available for comparison) is +1.5°.  This is entirely reasonable and falls within a range explainable by the specifications of the anemometer (± 5° accuracy) and the WXT (± 3° accuracy).

Similar analyses carried out at this buoy's sister stations at Buccoo Reef, Tobago (BUTO1) and Speyside / Angel's Reef, Tobago (ARTO1) found that the BUTO1 Compass directions can be divided into four distinct "regimes" with subsequent regime averages offset from one another by roughly 180°, and the ARTO1 Compass directions were stable throughout its deployment lifetime to date.  At BUTO1 the lifetime WDirDiff average is -18.6° and at ARTO1 the lifetime WDirDiff average is -11.4°, which suggests that at both Tobago buoys the wind instruments may not be properly oriented with the divergence being more significant at BUTO1 compared to ARTO1.

The complete analyses for the other WDirDiff/Compass averages, including graphs, may be found at this link for BUTO1 and at this link for ARTO1.

(signed)
Mike Jankulak

AirT/RH performance at Little Cayman, 2013-present

This post is part of a planned series of posts to share the results of my recent evaluation of data produced by all of the CREWS/CCCCC buoys over their lifetimes, from 2013 to the present.  This post will discuss the performance of the analog instruments which measure air temperature (AirT) and relative humidity (RH).  These analog reading serve as a basis of comparison for AirT/RH measurements reported by the Vaisala Weather Transmitter (WXT) which also reports wind, barometric pressure and precipitation data.

At Little Cayman the analog AirT/RH sensor's first deployment lasted 226 days before both the AirT and RH data simultaneously went bad on June 6, 2014.  [All instruments on a CREWS/CCCCC buoy are intended to produce usable data for an entire year.]  The buoy was brought to land for an annual maintenance operation on October 14-29, 2014 and suffered a power loss on December 29, 2014 that was repaired on land before redeployment on March 12, 2015.  The AirT/RH appears to have been successfully repaired/replaced during the October 2014 operation and has produced reasonable data since then.  This amounts to 150 days of reasonable AirT/RH data and counting, or 223 days and counting if you assume that the sensor would have operated properly during the buoy's extended power outage.

Note that at the time of the buoy's March 2015 redeployment it was discovered that the WXT communications had failed, so as of this writing there are no redundant AirT or RH readings available to compare against the analog AirT/RH readings.

The following are graphs of AirT (top, in °C) and RH (bottom, in %) from the Little Cayman buoy's lifetime, from 2013 to the present.  Values reported from the analog sensor under discussion are in blue and values from the WXT are in red.  Data are shown through June 9, 2015.

Please click on this image to see it in larger form.

Based on this data record the CCMI2 (Little Cayman) buoy's AirT/RH sensor performed reasonably well for 376 days out of the buoy's 506 operational days, or about 74% of the time.  Its longest stretch of proper operation was 226 days, or about 7.4 months.

Similar analysis performed on this buoy's sister stations at Buccoo Reef, Tobago (BUTO1) and Speyside / Angel's Reef (ARTO1) found that the BUTO1 instrument performed reasonably well for 90 days out of the buoy's 469 operational days, or about 19% of the time, and the ARTO1 instrument performed reasonably well for 181 days out of the buoy's 557 operational days, or about 32% of the time.  The BUTO1 sensor's longest stretch of proper operation was 90 days, or about 3.0 months, and the ARTO1 sensor's longest stretch of proper operation was 181 days, or about 6.0 months.

The complete analyses for the other AirT/RH sensors, including graphs, may be found at this link for BUTO1 and at this link for ARTO1.

(signed)
Mike Jankulak