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Narod Intelligent Magnetotelluric System (NIMS) field deployment Aug 7, 2007 John Booker (booker@ess.washington.edu) This documentation covers deployment of NIMS with either 8 hz (EMSOC) or 1 hz (USARRAY) configuration, PC104 circuit card format and MT-01 rev2 data loggers. Sections at the end cover the HP200 Palmtop computer used as the communication interface and the MT-01 rev1 data loggers. Important Warnings Narod Intelligent Magnetotelluric System (NIMS) field deployment
Aug 7, 2007
John Booker (booker@ess.washington.edu)

This documentation covers deployment of NIMS with either 8 hz (EMSOC) or 1
hz (USARRAY) configuration, PC104 circuit card format and MT-01 rev2 data
loggers. Sections at the end cover the HP200 Palmtop computer used as the
communication interface and the MT-01 rev1 data loggers.

Important Warnings

1. Never connect a solar panel to the external battery input. This can
damage the NIMS.
2. Never connect the system ground (pin A on the E-field input connector) to
an external battery terminal or a solar panel wire. Inadvertently connecting
the green wire to the positive battery terminal will damage the NIMS. It is
best to use a separate ground stake for the battery negative if added
lightning protection is desired.
3. Always remove the Compact Flash (CF) memory card before turning off
the NIMS.
4. Turn the NIMS off before closing it for transport. Failure to do so will
slowly discharge and may damage the internal battery.
5. Be certain that the NIMS lid is installed correctly when closing it in the field
and that no foreign object is caught in the lid seal.
6. Be sure that the manual pressure-relief valve on an older Pelican case is
closed (turned tightly clockwise) for field use and open (turned counter-
clockwise) for transport.
7. Read the warning on the internal battery cover before charging.

Physical Installation

NORTH
Magnetometer sensor














WEST
EAST

1

The magnetometer sensor head is buried in a vertical hole so that its top is
about 10 cm below the ground surface. It must be placed in one or two plastic
garbage bags before slipping into the hole. Dirt is packed tightly around the
sensor housing and firmly tamped down with something like a pick-axe
handle. During this filling process, the sensor top must be roughly leveled with
a bubble level and oriented with a compass so that the white covers on the
leveling knobs are aligned along an east-west line (see picture). After final
orientation and leveling (see Phase I of the Data acquisition startup section
below), the plastic bags are taped closed around the cable. The sensor cable
must be buried in a trench and may be further protected with plastic conduit
or rubber hose if the there is danger of it being dug up by predators. Finally, it
is good to cover the sensor head with a mound of dirt about 30 cm high. In
situations where digging is impossible, the sensor can be installed in a rock
cairn (pile) above the surface. If possible, use low magnetic susceptibility
rocks and cover the cairn with impermeable material (such as a plastic tarp)
to prevent air circulating easily through the cairn.

Electric dipoles

Electric dipoles should be about 100 meters long and be laid out in
geomagnetic coordinates. Dipoles as short as 40 meters have been used
successfully with high quality electrodes. Electrodes should be buried at least
30 cm below the surface. Electrode wires should be either buried or run in
plastic conduit if they are likely to be disturbed by animals. Placing rocks on
the wires every meter or less can be used if no other alternative is available.
Twisted connections between the electrode pigtails, electrode wires and the
NIMS connector pigtails should be carefully taped to prevent water
penetration. Corrosion of this joint can be a significant source of noise. The
NIMS pigtails are coded with knots as follows:

0 knots system ground (a metal stake is good enough)
WARNING: NEVER connect this wire to an external battery
or solar panel. Use a separate stake to ground battery or
solar panel negative for added lightning protection.
1 knot North
2 knots East
3 knots South
4 knots West

It is recommended that dipole wires be coded the same way. After
installation, measure the DC, AC voltages and resistance of each dipole.
Make any resistance measurement quickly, because the DVM voltage will
disturb the electrode potentials. This disturbance can be reduced by making a
resistance measurement in the forward and reverse direction for equal

2 amounts of time. If a dipole voltage exceeds 30 mv DC or AC, the NIMS
gain must be set to low for that channel. This is discussed further later.

NIMS electronics box

The NIMS electronics box has four connectors on its right end shown in this
picture. A fifth connector for the comm-cable to the HP200 is on the front.




GPS antenna input
Power:
A: NC
B: +12 VDC (red)
C; - 12 VDC (black)
D: - Solar (green)
E: + Solar (red)
Magnetic sensor
E field
Y
X Test studs for
E-field gain:
Open circuit to
ground means
low gain




The NIMS box shown is an ECS case made of fiberglass. Connectors on
Pelican cases have slightly different layout, but differences are obvious.



Charge
controller LED
E-field preamplifier

ON/OFF switch
AC/DC coupling switch


Inside the right end of the NIMS is a silver box with the E-field pre-amplifier.
The switch on its side (fiberglass boxes) and on its top (some Pelican boxes)
controls whether a high-pass filter is enabled (AC-coupled) or there is no
high-pass filter (DC-coupled). In order to flip this switch it is necessary to pull
the toggle away from the preamp box. It is purposely made difficult to do. This
filter is a single pole Butterworth filter with a nominal time constant of 6,000

3 seconds which suppresses electrode drift. The 3db point for this filter is at a
period of 37,700 seconds. EMSOC NIMS in Pelican cases with no switch on
the preamp boxes have a time constant of 30,000 seconds (3db period of
188,500: seconds 2.2 days).

The ON/OFF switch is just inside the power connector at the same end as the
preamplifier. This switch has a momentary contact either way and is
otherwise centered. Next to this switch is a green LED that is lit when the
solar panel input is delivering enough power to charge the battery. This LED
flashes about once per second when the solar panel is generating more than
about 14.5 volts and the battery is nearly fully charged. A solar panel will
charge BOTH the internal battery and any external battery connected to pins
B and C of the power connector.

WARNING: Connecting a solar panel to the battery input of the power
connector can damage the NIMS. ALWAYS connect the solar panel only to
the red/green power leads; NEVER connect a solar panel to the red/black
battery leads.

After the data acquisition has been started, the NIMS box seals should be
inspected for damage or foreign objects and the top lid should be closed. Do
not try to fix problems with grease. The latches should be made tight. The
NIMS and any external battery should then be placed in plastic garbage bags
and buried in a hole so the shallowest part of the NIMS is at least 20 cm
below the ground surface.

WARNING: The NIMS should NEVER be buried with its handle or lid at the
bottom because the leak detector sensors will not function properly in these
positions.

The bags should be tightly taped where the cables come out of the bags and
the tops of the bags should be as high as possible in the hole to retard water
entering. Although NIMS are highly water-resistant and have internal
protection that turns them off in the event that they get wet inside, it is best
not to test these protective features.

WARNING: Fiberglass boxes are not watertight unless their lid matches the
box and the serial numbers on the lid and the box are on the same side of the
box. Older Pelican cases with pressure equalization valves that must be
closed by hand are not watertight unless these valves are screwed firmly in a
clockwise direction.

It is recommended that the NIMS and battery in the hole be covered with a
thermal shield such as a space blanket. The silver side is placed down
towards the NIMS and the orange side is up. ¼ of the type of space blanket
typically sold at outdoor stores such as REI is large enough to wrap over both

4 NIMS and battery and down their sides. After placing the thermal shield, the
hole is back-filled with dirt. Be sure that the GPS antenna is on or very close
to the ground surface and is not inside the space blanket. This is because
space blankets use a thin layer of aluminum that is opaque to GPS signals. If
burial is not possible, a rock cairn or the shade of a tree or bush can be used.
Cover a cairn to prevent air easily circulating through the rocks.

WARNING: Bears have dug up and mauled NIMS boxes. If