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Subject: Data loggers

Data loggers

From: Walter Henry <whenry>
Date: Tuesday, May 7, 1991
>ACR Stick-on data loggers???  Rustrak???  I'm lost!  I assume these
>are devices for measuring temperature and relative humidity(?) and they
>may or

Data loggers are electronic devices that record signals from a sensor or
other signal source. (My answers from this point on will apply to the
sorts of devices/applications we are likely to use in conservation, but
be aware that there are all sorts of devices used for other purposes
that have different characteristics.).

Data loggers record a signal generated by a sensor (such as a temp
sensor, rH sensor, pH electrode (suitably conditioned), all sorts of
meteorological sensors, etc).  The sensor (normally) provides a
continuous analog signal and the data logger samples from that signal
(usually at a fairly high (for our purposes) sampling rate (many
times/second)), digitizes the data and saves it.  After a recording
session (which can last anywhere from a few minutes to several months),
you download the stored data into a computer and use one or more pieces
of software (normally provided by the data logger manufacturer) to view,
analyze, and graph the data.  Thus these devices can be used to replace
the traditional hygrothermograph, whose functionality they exceed (ie
everything you can do with a hygrothermograph you can do with a
data logger (assuming you have a temp/rh sensor(s)) and then some.
typical data loggers allow multichannel recording, so you could plug in
additional sensors if you want (I can't think of a good case when you
would do this, but someone will come up with one soon).

>may not be connected to a computer(?).  What exactly are they?  How
>much do they cost?

Costs range from a few hundred dollars up to many thousands.
Fortunately, for our purposes, the less expensive instruments are
adequate (the more expensive instruments are more robust to drift, which
is a serious matter if you are doing measurements in parts-per-billion,
but not for the relatively crude sampling we do).

>Where do you get them?  How do they interface with a computer?

>From metereological houses, science houses, directly from the
manufacturer.  Interface is typically through a standard serial (RS232)

>If connected to a computer how often are they checked - continuously?
>hourly? How is the data saved?  If they are not connected directly to a
>computer how is the data retrieved?

Normally, the data logger is a remote recording device that runs on
batteries or an AC adapter during recording.  It is then brought back to
the pc, attached via the serial port, and the data downloaded.  It is
not necessary to have the computer at the recording site (except, in the
case of the ACR, as noted by Paul).  In the case of the Rustrak Ranger
(and probably other units as well), it is possible to get realtime
readouts from the logger without connecting it to a pc.

I will send you (separately) some additional information on the
rustraks, acr's and Data Bears.


                  Conservation DistList Instance 4:58
                  Distributed: Saturday, May 11, 1991
                        Message Id: cdl-4-58-008
Received on Tuesday, 7 May, 1991

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