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Subject: Hygrothermographs


From: Paul N. Banks <pbanks>
Date: Tuesday, April 10, 1990
I am frequently asked, as I assume others are, what brand of
hygrothermograph to buy.  I feel that it is a bad time to have to buy a
"conventional" (non-electronic) instrument because we will soon be able
to recommend electronic instruments that have many advantages, but there
are still times when a conventional instrument seems necessary.  There
are many brands now of conventional hygrothermographs, but their basic
elements are essentially similar: organic RH sensing element, bimetallic
(or similar) temperature sensing element, clock, pens, paper chart.  The
major basic differences are the clock drive: windup or battery, and 1,
7, or 30 days.

It does seem to me that a battery-operated quartz clock drive is
inherently better than a wind-up one.  Not only is it more convenient
and probably more accurate, but it eliminates the weekly shaking-up of
the instrument.

Also fiber pens are certainly more convenient than the pesky older metal
nibs that usually led to purple ink all over everthing when trying to
refill them or make them feed.

However, in my own experience, there are quite significant differences

    1.  Ease of resetting (how accessible are the knobs or other means
        of resetting; the ratio of motion of the knob to pen
        motion--that is, can one adjust the pen a small distance without

    2.  How well the instrument holds its setting (does drift out of
        calibration frequently)

    3.  How much maintenance is require (beyond chart changing and
        periodic calibration)

    4.  Ease of maintenance and service (can one replace parts oneself
        or does it have to be sent to the maker; how satisfactory is
        service from the maker)

The only way to obtain *this* kind of information about instruments is
through actually using them, not from product literature. It would be
useful to me (and I presume to others) to try to compile some of the
experience that people have had with different brands.

Thus I am asking readers of the Cons Distlist to share their
experiences.  If there is sufficient response, I will summarize and post
on the list.  It would be useful to have specific maker's (not just
supplier's) names and model numbers.

Paul Banks

                   Conservation DistList Instance 3:6
                 Distributed: Saturday, April 28, 1990
                        Message Id: cdl-3-6-001
Received on Tuesday, 10 April, 1990

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