Rebecca,
I own two recording hygrothermographs.  One has a single hair bundle for
monitoring %RH and the other has 8 hair bundles; both use bi-metallic
strips for recording temperature.

In addition, I own three data loggers.  Two were designed to work with
Macintosh computers, and one was designed to work with PC's.

And then, there is the Micronta temp/%RH LCD device from Radio Shack.

The Radio Shack device (manufactured in China) cost about $30.00; the
other units cost from approx. $400 - 900.

Bi-metallic strips are about as good as it gets.  Simple technology; as
close to bulletproof as it gets in this game.  Hair bundles are
different.  They are as accurate as the last re-callibration, so long as
there has not been a major humidity change (rain storm, for instance).

Data loggers are generally superior to paper chart, recording-
hygrothermographs, in my opinion.

Data loggers have their own problems, to be sure, but I have the capacity
to calibrate the sensors.  These are containers of saturated salts into
which I may introduce the sensors.  The saturated salts, and the
temperatures, are thus known, and if the sensors indicate drift, the
software can be notified (in a sense) and appropriate changes may be made
to the formulae which interpret incoming data.

Recording hygrothermographs may provide a "written" record of change in
temperature and relative humidity over time.  Data loggers provide the
same information in a digital format which permits a degree of analysis
of conditions which is not possible with paper chart recorders.

Arguements are raised to the effect that data loggers do not provide a
continuous record, and that recording hygrothermographs do provide such a
record.

Examine a paper chart from a museum.  The paper chart machine may be
continuous, but the physical plant (furnace/air conditioner) kicks in or
out in 15 - 30 minute units of time.

A data logger set to reach out and record every 15 minutes, or 30
minutes, will provide a useful record.

In addition, data loggers may be tied into an alarm system more easily
than paper chart recorders.  This may wake a museum director or curator
up in the middle of the night, but that may be a small price to pay.

Jack C. Thompson
Thompson Conservation Lab
Portland, OR

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On Wed, 13 Mar 1996, Rebecca Patchett wrote:

> Hello.  I have recently become aware of the relatively inexpensive option of
> purchasing RH and temp. sensors (known as data loggers) that record
> environmental data continuously and store it internally in a microchip (ex,
> ONSET brand).  This data is downloaded into a computer at a later time in
> order for it to be read.  The sensors are tiny, and very affordable compared
> to the recording hygrothermographs that are larger and use graph paper.
>
> I believe the data loggers were originally designed for biological studies,
> field use, and the like.  I was wondering if anyone has experience with these
> loggers in museums.  If so,  are they worthwhile for museum
> applications?  How do they compare with the "standard" recording
> hygrothermographs I/we are more familiar with?  How is the accuracy of these
> small units?  We are considering them as a cost effective option for a small
> museum.  Any comments are greatly appreciated!
>
> Thank you,
>
> Rebecca Patchett
> Lilah C. Holden Elephant Museum
> Portland, OR
> e-mail:  [log in to unmask]
>