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]
>
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