Monthly Science: Basement Safe Humidity

A plot of the temperature and humidity inside the basement safe over the last year-and-a-half:

Basement Safe
Basement Safe

The tray of silica gel (or whatever those granules might be) holds the humidity firmly at 14 to 15 %, at least with a simple masking tape seal around the door opening that dates back to early 2012. Less water vapor gets through the door during the winter, due to the lower basement humidity when it’s cold outside, but it looks like four regenerations per year with just under a kilogram of desiccant in the tray.

Ordinarily, it’d be time for those granules to endure another oven session, but I just picked up a bunch of real silica gel beads and must conjure up some porous bags.

The Bash / Gnuplot script that cleaned the CSV files and produced the plot:

#-- overhead
export GDFONTPATH="/usr/share/fonts/truetype/"
echo Base name: ${base}
echo Input file: $1
echo Temporary file: ${tfile}
echo Output file: ${ofile}
#-- prepare csv Hobo logger file
sed 's/^\"/#&/' "$1" | sed 's/^.*Logged/#&/' | sed 's/ ,/,/' | sed 's/\/\([0-9][0-9]\) /\/20\1 /' > ${tfile}
#-- do it
gnuplot << EOF
#set term x11
set term png font "arialbd.ttf" 18 size 950,600
set output "${ofile}"
set title "${base}"
set key noautotitles
unset mouse
set bmargin 4
set grid xtics ytics
set timefmt "%m/%d/%Y %H:%M:%S"
set xdata time
set xlabel "Date"
set format x "%y-%m"
#set xrange [1.8:2.2]
set xtics font "arial,12"
#set mxtics 2
#set logscale y
set ytics nomirror autofreq
set ylabel "Temperature - F"
set format y "%3.0f"
set yrange [40:90]
set mytics 2
set y2label "Relative Humidity - %"
set y2tics nomirror autofreq
set format y2 "%3.0f"
set y2range [10:60]
#set y2tics 32
#set rmargin 9
set datafile separator ","
#set label 1 "label text" at 2.100,110 right font "arialbd,18"
#set arrow from 2.100,110 to 2.105,103 lt 1 lw 2 lc 0
plot    \
    "${tfile}" using 2:3 axes x1y1 with lines lt 3 title "Temperature",\
    "${tfile}" using 2:4 axes x1y2 with lines lt 4 title "Humidity"

3 thoughts on “Monthly Science: Basement Safe Humidity

  1. That is one deeply suspicious-looking graph. You sure you’re not below the detection limit or have missing samples or somesuch? No line should be that flat…

    1. No line should be that flat…

      Now that I consult the datasheet, it turns out that the poor thing is good down to 25 % RH… so 15 % must be its way of saying “Too low to mention!”

      On the other paw, the RH climbs upward from that level pretty much as you’d expect, so it’s not holding a grudge.

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