ABEM Terrameter SAS 1000 / SAS 4000
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As in resistivity mode the current amplitude is set automatically by the instrument, but can
also be controlled by the operator. It can be set to values from 1 mA up to 1000 mA. The
maximum voltage at the current electrodes is 400 V.
In the induced polarization mode (IP) the SAS 1000 / 4000 measures the transient decay of
the voltage when the transmitted current is turned off. The voltage is integrated over a number
of time intervals, and the SAS 1000 / 4000 can measure in up to ten such time intervals. The
total integration time is limited to 8 sec. The first interval starts after the initial time delay
t
d
. The length of the different time intervals can be expressed by the relation
t
n f
t
i
i
=
−
1
0
where
•
t
0
is the fundamental time interval (20 msec in areas with 50 Hz main power frequency,
respectively 16.67 msec in areas with 60 Hz power frequency)
•
n
is a multiplying factor (default = 1)
•
f = 1 or 2
(default
f = 2
) is an incremental exponent
•
i
is the time window index (1, 2, ... , 10)
Four parameters are needed in order to specify the way SAS 1000 / 4000 measures the
induced polarization:
•
The initial time delay (10, 20, 30, .... msec). Default is 10 msec. Maximum is 10 sec.
•
The length of the first time window (column one in the tables below). Default is 100 msec.
•
The number of time windows (from one to ten). Default is 1.
•
The incremental factor: 1 corresponding to the first of the tables below, 2 corresponding to
the last of the tables.
Period
Current
Voltage
Measuring intervals
Figure 2. Timing diagram of the Terrameter SAS 1000 / 4000 in IP mode. The full-drawn
curve shows the transmitted current, and the dotted curve an example of the
measured decaying voltage in the presence of noise. In this example there is almost
no IP effect. The two receiving intervals are shown at the bottom line. Each
measuring interval can consist of up to ten time windows.
