ABEM Terrameter SAS 1000 / SAS 4000
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layers. This (paradoxical) behaviour is explained quantitatively in the literature
4
. Near-surface
objects can also cause negative IP readings, see e.g. Principles of Applied Geophysics
5
section 5.6.
2.4.4
DC potential measurement (SP)
If the SP option is chosen in the Main Menu, DC potential (self-potential) measurements can
be done. Thanks to extremely linear circuits, the voltage can be read and displayed to 3 or 4
significant digits.
The basic integration interval is 20 msec (16.66 msec in countries with 60 Hz power line
frequency). This integration gives an effective reduction of noise. In areas close to electric
railways with 16 2/3 Hz frequency it is recommended to select 100 msec integration interval.
The Terrameter SAS 1000 / 4000 calculates either the mean or the median value (default).
The standard deviation of the measurements are also calculated and presented. Statistically
distributed voltage noise is thus reduced by a factor of
N
, where
N
is the number of
readings. Measure time can be 1 - 8 sec in steps of 0.1 sec.
2.5
TECHNICAL LAYOUT OF THE SAS 1000 / 4000
The SAS 1000 / 4000 is equipped with a PC-compatible microcomputer and controlled by
four knobs (Figure 5). Each knob is mounted on a peg, fixed in the instrument panel, and the
motion of the knob is transferred magnetically. This ensures waterproof sealing.
For a detailed description of the user interface, please refer to chapter 3. The program allows
the user to specify the measuring parameters in detail, and even put comments on the data
files. However, for those who want simply to take a reading, there is no need for setting
parameters. Just hit the red knob.
4
Nabighian, Misac N., and Elliot, Charles L., Negative Induced-Polarization Effects from Layered Media, Geophysics 41,
6A, p1236-1255.
5
Parasnis, D.S., Principles of Applied Geophysics, Fifth Edition 1997, Chapman and Hall.
