Recording hygrothermographs and dataloggers

Tom Dixon <tom.dixon [at] ngv__vic__gov__au> writes

>I would be grateful to hear from the list regarding positive and
>negative experiences of replacing recording hygrothermographs used
>for simultaneous monitoring of several large gallery spaces on a
>long term and continuous basis with newer technology.

We have used and experienced most forms of recording temperature and
humidity and each has its own strengths and weaknesses. Telemetric
data loggers are the easiest and least time consuming once they are
set up and running correctly. The environmental data  is relayed at
set intervals (say 30 minutes) to a base station (computer) from
sensors placed throughout the building. In many circumstances
boosters are needed to help the signals reach the base station from
the sensor. You can then easily check the charts as often as you
like. You can view the chart by the hour, day, week, month or any
time span you need. You can compare charts and easily use the
information gathered. Provided the computer is dedicated to this
process you can usually see the live data on the screen. Obviously
if you use the computer for other purposes the live data is not
visible. The sensors can include a small screen so that you can read
the conditions off them.

This type of system becomes economic if you need about 5 or more
recording thermohygrographs, (i.e. when I last worked this out for
the UK the cost of 5 recording thermohygrographs was roughly similar
to a telemetric data logging system after that the telemetric system
begins to become more economic).

The disadvantages are that you need help setting the system up and
it is no good if you don't like working with computers; also you can
find yourself examining the charts in minute detail but not actually
looking at the objects. At least changing the papers gets you round
the galleries. The advantage of the recording thermohygrographs is
that they are mechanically simple, work in building sites and clean
galleries, are easy to calibrate and maintain and there is not much
to go wrong but they are large, relatively expensive and take up
time with changing charts.

A telemetric system can also be installed in remote building, such
as stores or annex where the data is gathered and then sent via a
modem to the base station.

Finally, never trust the building management data logging system.
The sensors are placed in the ducting and not near your objects.
With a system dedicated to the collection you know when it has been
calibrated, how reliable it is, you can place it where you want.

Frances Halahan
Halahan and Associates, Conservation consultants
London UK.


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                  Conservation DistList Instance 14:46
               Distributed: Wednesday, February 21, 2001
                       Message Id: cdl-14-46-005
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