[Greenbuilding] warning, more than most want to know about hygrometers, details

[Sacie Lambertson]

For those who want to read more about these instruments, I pulled this off
an Amazon review of the Caliber III hygrometer:  S


I do environmental surveys as part of my professional work and use a
variety of expensive analog and digital instruments, thermometer wet/dry
bulb psychrometers, multi-hair recording hygrothermographs, some
instruments with NIST certification (but not mirror instruments). I've
bought several analog and digital hygrometers costing under $150.00
(including the Caliber III) to play with and check for use by my daughters
who humidify and dehumidify their living and storage spaces for violins and
violas. I give this little instrument 5 stars for being accurate for its
price - certainly accurate enough for musical instrument storage, cigar
humidors, and basic building environmental monitoring. However, don't
expect that "accurate" means what the instrument displays is what the
environment really is. And do not expect these inexpensive instruments to
all read the same. All the inexpensive instruments I purchased and all my
professional instruments costing into the thousands do not give exactly the
same readings when placed together in a controlled climate chamber. Do not
expect a lot of precision in humidity measurement for a number of factors
too complicated to go into here but related to particles and various
gaseous molecules in the air. For most instruments costing under $150.00
reading, let's say, 50% RH, just believe the RH is in the range 46-54%. For
instruments up to $1,000, a 50% RH reading probably represents actual RH of
48-52% RH. Do not expect more. One other thing you must know about digital
hygrometers, and this is critical to recognize, they are fast and accurate
(again within reason) and they quickly read their local environments which
includes your body heat, skin moisture, breath moisture, and varying
temperature and humidity in local air currents you may not even feel. You
are a walking cloud. Certainly don't hold one and expect it to match
another instrument sitting next to it on a shelf! The heat of your hand
warms the plastic case raising the temperature reading and thus also
drastically affecting RH. Don't even stand within three feet of one and
expect it to match the display of one four feet from you. Also, this
digital instrument and others like it will detect and display numbers
representing the real differences in the environment that can exist just
inches apart. That's why two of the same instruments next to each other may
not match - its not bad quality but high sensitivity. This speed and
accuracy of even inexpensive hygrometers is probably the sole cause of
people complaining about "inaccuracy" of digital hygrometers and the
frustration they experience. For more information related to how difficult
it is to really get accurate RH readings and difficulty in calibration read
reprinted articles on the Veriteq website. If you want just "a little more
accuracy", you can get "a little more accuracy" by paying a few extra
hundred dollars, like over $500 for a Vaisala HM34. For the price, and
considering how nearly impossible it is to get a true measurement of RH,
maybe its good enough for you just to know, for example, "well, the RH is
somewhere between 50 and 60 according to this instrument." Even knowing
this a digital hygrometer's speed and sensitivity can still make one feel
frustrated.
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