ABEM Terrameter SAS 1000 / SAS 4000
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The current amplitude is set automatically by the instrument, but can also be controlled by the
operator to suit the actual survey conditions. It can be set to values from 1 mA up to 1000
mA. The maximum voltage at the current electrodes is 400 V. It is recommended to use the
AUTO setting, which implies that the instrument sets the optimum value.
In the resistance measuring mode, the Terrameter SAS 1000 / 4000 measures voltage
responses created by the transmitter current while rejecting both DC (SP) voltage and noise.
The ratio V/I is automatically calculated and displayed digitally in kiloohms [k
], ohms [
]
or milliohms [m
]. The relevant receiver resistance range is automatically selected.
The result is displayed to 3 or 4 digits. When the transmitter is operating at 500 mA, the
Terrameter SAS 1000 / 4000 has a resolution of 0.02 m
for a single reading.
To take full advantage of the outstanding capabilities of the Terrameter SAS 1000 / 4000, care
must be observed in the arrangement of cables and electrodes used in the field. Current
leakage and creep can substantially reduce the attainable accuracy and sensitivity and thus the
depth penetration.
2.4.2
Induced polarization mode - Chargeability
In IP mode the current is transmitted symmetrically, i.e. that the positive and negative
polarities are of equal length. A complete cycle consist of one positive part of length T (called
current on) and one negative part of the same length T (current off). This time can be set to
the following values: 1, 1.5, 2, 2.5, 3, ... sec in steps of 0.5 sec.
Period
Current
Voltage
Receiving intervals
Figure 1. Timing diagram of the Terrameter SAS 1000 / 4000 in resistivity mode. The full-
drawn curve shows the transmitted current, and the dotted curve an example of
the measured voltage in the presence of noise. The three receiving intervals are
shown at the bottom line.
