[CAUT] Reading low humidity

[Roger Wheelock]

Hi Fred and Debbie,

While this device is quite affordable, the spec. sheet lists the relative 
humidity accuracy between 20-80% RH as +/- 3.5%, rising to +/- 5% at the 
extremes.  They also list annual drift at 1% and offer no means (that I can 
see) for recalibration.  The added cost over their temperature-only data 
logger is $20.  This cost differential means there must be a low-end sensor 
for humidity, similar to a $25 hygrometer.

By comparison a Dickson data logger is +/- 2% from 0-95% RH.  These drift 
downward 1% per year.  They can be recalibrated.  The bad news is they cost 
about $270.

Our experience is that performance improves with increasing price for most 
electronic hygrometers and data loggers.  We have yet to see one that 
shouldn't be recalibrated annually.  However, even when a unit drifts, it 
can give accurate differences between two humidities.  This means that the 
reading will become less accurate over time but the difference between a 
max. and min. reading will stay fairly constant.

Roger
Dampp-Chaser Corp






----- Original Message ----- 
From: <DCyr141833@aol.com>
To: <caut@ptg.org>
Sent: Thursday, March 02, 2006 11:43 AM
Subject: Re: [CAUT] Reading low humidity


> Fred, and others
> I have recently found a nifty little device that seems to read humidity 
> and
> temperature quite accurately.  It's a sensor, not a gauge that you can 
> look
> at and read instantly, but it tracks temp, humidity and dew point over a
> period of time (you decide if you want it to measure every half hour, 
> hour,  etc),
> it's got it's own built in USB port, you plug it into your computer, 
> download
> the data, and it prints out a graph and spreadsheet.  We've been  playing
> with it at the school for the past month and I'm quite impressed.
> _Data  Acquisition from Measurement Computing_
> (http://www.measurementcomputing.com/cbicatalog/USB-502.asp?dept_id=414&pf_id=1759&mscssid=7K4AT7KNBUQP8HEFNC
> 6WE99XMQNK1LN5)
> It's $79, with software.
> Like I said, it's not a gauge that you can just look at - but it does 
> track
> humidity down lower than anything else I've seen.
> Debbie Cyr
> North Bennet St. School
>