TRANSIENT ELECTROMAGNETICS PROGRAM
Section 12, Page 33 October 2002
12.18 THE NANOTEM SYSTEM
The NanoTEM system is a very fast turnoff and sampling TEM option available for the
GDP-32
II
receivers. The equipment consists of a high-speed sampling card (Board 194) for the
GDP, a battery powered NanoTEM transmitter and a few loading resistors.
The receiver board samples the decay waveform at either 1.2 or 1.6 microsecond intervals, and
then stores the data in an on-board memory buffer. Then the data are transferred to the main
GDP memory where the samples are combined to form time windows on a logarithmic scale.
The NanoTEM transmitter is configured for very fast turn-off, is powered by a 12-volt battery,
and can output up to 4 amperes. Two versions of the NanoTEM transmitter are available. The
first, the NT-20, is an external transmitter system, and the second is the NT-32 that utilizes a
transmitter integrated within the GDP-32
II
case.
Operating instructions for the NT-20 transmitter are included in a separate manual included with
the NT-20. Instructions for effective operation of the NT-32 system are included in Section
12.20.
NOTE: Board 194 has a fixed gain stage of x10, which cannot be changed. Therefore, the
receiver moment must be multiplied by a factor of 10 (as shown in Section 12.19, step 9) to get
the correct resistivity numbers. There is also a variable gain stage with selections of 1, 2, 4, 8
and 16, which can be set automatically with the NanoTEM program.
NanoTEM Configuration
NanoTEM Card for the GDP-32
II
NT-20 or NT-32 Transmitter
Wire for TX loop - 10 x 10 m, 20 x 20 m, etc.
Wire for RX loop - presently using 5 x 5 m by 1 turn for 20 m TX loops and 10 x 10 m
for 40 m TX loops.
Battery for NT-20 or NT-32
Battery charger
Cable: RX loop to GDP - twisted pair with 150 ohm load resistor with alligator clips
on the receiving antenna end and a 1 kΩ balanced bridge resistor on the other end,
which plugs into the GDP. The cable should be approximately 14 meters long for a
20 x 20 m loop.
Cable: transmitter control - from NT-20 to GDP
Cable: battery power for NT-20
Two options:
a) cable for using two 12 Volt car batteries
b) cable for using 12/24 Volt 10 amp-hour battery pack
CAUTION: NanoTEM operation requires 12-volt supply only.
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