----- 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
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