[CAUT] Reading low humidity

[Chris Solliday]

Fred, Debbie & List,
 I can only echo Roger's endorsement. I have been using the Dickson
DataLogger for some time and am very pleased with it. I have had three
different models but the one I use all the time now is the TR320 which has
the specs Roger mentioned, it is $229 but you need software and a cable to
make charts and graphs to scare folks with, and that costs $79 and if you
want to do recalibrations yourself that software is $249. All of which is
extremely useful and has paid for itself many times over in Chris's world. I
actually had the thrill recently of getting a university to alter their HVAC
settings based on the data I supplied. The secretary in the 79 degree office
is almost as grateful as the pianos in the hall that were toasting at 78 F
and 7% rh. I've even measured, quite accurately I'm sure, at other venues,
3% recently. The TR320 also works at the piano as I am tuning, as I used to
do with my Pianotek box, with its 2.5 digit LCD and BTW it will record up to
32,000 sample points over just about any duration you choose. I just wish it
could dance. We'd have such a time me and my TR320.
 Chris Solliday
 it's late so go easy
----- Original Message ----- 
From: "Roger Wheelock" <roger@dampp-chaser.com>
To: "College and University Technicians" <caut@ptg.org>
Sent: Thursday, March 02, 2006 2:37 PM
Subject: Re: [CAUT] Reading low humidity


> Hi Fred,
>
> With Dickson units we see a fairly repeatable 1% RH drift per year
downward
> when compared to a US secondary standard hygrometer we use to calibrate
our
> humidistat switches.  I am not sure of the direction of drift for all
> sensors.  My understanding is that airborne pollutants coat the plates in
> the sensors, giving a variation in the reading with time.  I believe most
> sensors measure capacitance of the air between two small closely-spaced
> plates.  I think there are also some that measure resistance.
>
> Roger
>
> ----- Original Message ----- 
> From: "Fred Sturm" <fssturm@unm.edu>
> To: "College and University Technicians" <caut@ptg.org>
> Sent: Thursday, March 02, 2006 2:11 PM
> Subject: Re: [CAUT] Reading low humidity
>
>
> > Hi Roger,
> > How much annual drift do you see on the Dickson? Is it always in a
> > particular direction? Does that apply to any electronic sensor
(direction
> > of drift)? Is drift caused by "accumulation of  crud" (sensor getting
> > dirty, picking up air pollution, etc)? Or is  there something else
> > involved? I've got a bunch of other questions  bubbling to the surface
as
> > well (how does an electronic sensor work  in
physical/electrical/chemical
> > terms . . .), but any enlightenment  you can provide along these lines
> > would be most appreciated.
> > Regards,
> > Fred Sturm
> > University of New Mexico
> > fssturm@unm.edu
> > On Mar 2, 2006, at 11:28 AM, Roger Wheelock wrote:
> >> 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
> >
> > _______________________________________________
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> >
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