Hygrometer

[Delwin D Fandrich]

----- Original Message -----
From: "Farrell" <mfarrel2@tampabay.rr.com>
To: <pianotech@ptg.org>
Sent: August 31, 2002 10:53 AM
Subject: Re: Hygrometer


> Del, what brand and model of hygrometer do you use? And about what was the
price?

The hygrometer we use is a motorized version of a sling hygrometer. Wet one
bulb, turn on the switch and a little motor starts up pushing a fixed amount
of air past the two bulbs. We then check the two temperature readings
against a standard chart furnished for such things. The price was basically
the cost of cleaning out the battery compartment--and getting the ancient,
heavily corroded batteries out--and rebuilding the thing. I rescued it from
the trash heap out back of the company that was throwing it away.


>
> Do you recall the stated accuracy of the RH reading in the area of RH and
temps. you commonly encounter with your boards?

We also have an electronic hygrometer made by Vaisala. I don't remember the
model number off hand. It has a claimed accuracy of +/- 2% between something
like 0º and 140º F (approximately). It cost somewhere around $300 ten or
twelve years ago. A new sensor will cost around $100 (plus shipping) so it
also sits in the bottom drawer while we use our wet/dry bulb instrument that
just keeps plugging along.


>
> Do you calibrate your instrument?

There is no way (or need) to calibrate a wet/dry bulb system. The electronic
one will get calibrated if and when we ever send it in to get the sensor
replaced. (It got dropped some years back--it wasn't the fault of the
instrument.)

In theory, electronic hygrometers should be calibrated every year or so to
maintain stated accuracy. In reality the newer ones using various synthetic
sensing elements are proving to be relatively stable.


>
> I'm just trying to get a feel for where the accuracy comfort level is for
a rebuilder/builder/designer with your experience. Thanks.

Go back and read Ron's missive on the subject--he pretty well covered it. We
try to keep pretty close tabs on the conditions in our conditioning room--we
do check it every day--but we're not fanatics about it. Then, our climate is
pretty benign. Wood moisture content hovers around 8 -10% year-round.

Del