Sensor failures & battery leaks meant that I had to rebuild some of the drip loggers retrieved last week, in addition to loading all the units with the latest code tweaks for sensitivity, buffering, etc. Because the latest loggers have improved so much, Trish keeps telling me to retire the mixed bag of first-gens. But the maker geek in me just can’t resist the urge to give those aging units another run just to see how long they will last. (perhaps there’s a bit of self identification there..?) I’ve heard some of my coder friends refer to this kind of thing as a one tweak loop; often in association with tales of corporate disaster. Fortunately, the hard time constraints of fieldwork are more than enough to curtail my mild O.C.D because when deployment day arrives, you either have it in the bag or you don’t.
And this time round we had more than twenty units going in. This was the reason that Trish & Fernanda had done so much surveying on our previous day at Rio Secreto. While they were taking measurements, I joked with Trish about playing Goldilocks in a chamber that was literally heaving with beautiful stalagmites, but the truth is picking a good one that doesn’t introduce a sampling bias, is a heck of allot more challenging than you might think. I left her to sort that out and do the manual counts, because I was so keen to get the two Masons hygrometers installed. I’m hoping that the DS18’s can deliver another success, like we saw with the underwater temperature strings.
The key to this approach is that the wet bulb is hydrated by the run-off from a drip sensor station, hopefully allowing us to operate for long periods of time at these unsupervised locations. So those DS18’s have a very long wick wrapped around the rim of a drip logger with a cable tie. Encouraging evaporation like this is probably going to cause some mineral deposition, and there are a dozen other problems listed in the textbooks. But I am going to give it a shot anyway because there are few things as satisfying as discovering something you’ve built actually works, when authoritative sources say it won’t.
And we also have a new SHT-11 humidity logger installed nearby. The sensor itself is the soil moisture rig from Seeed, with a copper sintered mesh over the sensor that could ‘theoretically’ withstand full immersion. I tried to suspend the sensor head so that random drips from above would be deflected away, but even with liberal amounts of silicone on that breakout, I’ll be happy if we get a month of clean data from it before it suffers the same fate at the HTU21D’s we tried earlier. That ought to be enough to calibrate the Masons.
Once we had the new toys in place, we could finish placement of the drip stations. A couple of the older stations suffered repeated knock-overs, so we decided to relocate those. One of the new sites was near a beautiful pancake-stack formation, but it only had a 12cm drip fall. That’s a very small amount of kinetic energy for my sensors to detect, and I watched this unit for 30 minutes to make absolutely sure the logger was picking it up. Though the drips made no sound at impact, the indicator LED was piping OK.
We wrapped up the day by putting the new logging rain gauges on the roof of a building, beside our solar shielded pressure/temp/r.h. sensors. My hope is that those funnels give us a more quantitative record from the little drip sensors in the base, in addition to protecting them from that merciless tropical sun.
Several people have pointed out to me that weather stations are getting pretty cheap these days, and then asked me why I don’t just use something off the shelf. Generally, I just get a weird look when I reply: “Sure, but where’s the fun in that?” Fortunately for Trish & I, the people at Rio Secreto understand, and they have allowed us to use a corner of their amazing cave once again for the project. Thanks again you guys!