Geometrics Geode EM3D Manuale utente
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Table of contents
Chapter 1: System Components -----------------------------------------------------------------------1
Introduction----------------------------------------------------------------------------------------1
Laptop Controller---------------------------------------------------------------------------------1
Network Interface Box (NIB)-------------------------------------------------------------------1
GEM3D Receiver----------------------------------------------------------------------------------3
Magnetic induction coils------------------------------------------------------------------------5
Electrodes------------------------------------------------------------------------------------------6
Ethernet cables-----------------------------------------------------------------------------------6
Chapter 2: Geode EM3D PC Controller setup------------------------------------------------------8
Chapter 3: GEM3D receiver setup-------------------------------------------------------------------11
Chapter 4: Software-------------------------------------------------------------------------------------18
Chapter 5: SAS (System Acquisition Software) --------------------------------------------------31
Chapter 6: Interface to a controlled-source transmitter -------------------------------------33
Chapter 7: CSAMT Processing-----------------------------------------------------------------------34
Chapter 8: MT Processing ----------------------------------------------------------------------------42
Scalar Processing -----------------------------------------------------------------------------52
Chapter 9: Factors determining good versus bad data for Controlled-Source Audio
Magnetotellurics: ---------------------------------------------------------------------------------------58
Chapter 10: General survey principles and typical survey operation-----------------------59
Chapter 11: Notes on AMT (natural field) versus CSAMT (controlled source) -----------60
Appendix 1: File and data structure----------------------------------------------------------------62
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Appendix 2: GPS Setup Software -------- -----------------------------------------------------69
Appendix 3: MT Theory-----------------------------------------------------------------69
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Chapter 1: System Components
A. Introduction: basic theory of operation, networking, and data acquisition
The Geode EM3D is a distributed network of EM receivers. Each receiver has six
channels which can be configured with up to three magnetic (H) channels and from
three to six electric (E) channels, depending on the number of magnetic channels used.
All receivers communicate to one another and to a PC Controller through a hard-wired
Ethernet backbone. The fundamental theory of MT, AMT, and CSAMT can be found in
a brief review in Appendix 1. Fig 1. shows a four-receiver network consisting of four
receiver modules with twenty E-field channels and four H-field channels.
Fig. 1 Network sample setup
B. System components: A typical Geode EM3D will consist of the following components:
1. Laptop controller with the acquisition software and processing software
2. Network Interface Box (NIB)
Fig. 2 Network Interface box
The picture in Fig. 2 shows the NIB with two cables. The large yellow cable
attaches to the Ethernet 10-pad connector on the NIB and the other end to the
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10-pad connector on the receiver box. The black cable with the RJ45 connector
connects to the RJ45 port on the PC Controller.
There are three positions to the NIM switch: “Battery Test”, “Enable Power
Down”, and “Enable Power Up’”. Details of NIB operation is given in section ***
below.
3. GEM3D Receiver: The six-channel GEM3D receiver is discussed in more detail
in the receiver setup section below.
Fig. 3: GEM3D receiver box
4. Magnetic Induction Coil: The Geometrics G20K coils operate on a band width of
0.1 Hz to 20k Hz. The operation range of the Geode EM3D CSAMT system is 0.1
Hz to 10 kHz. Coils specifications are available at www.geometrics.com or by
contacting sales@geometrics.com
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Fig. 4: G20K magnetic coils.
5. Electrodes: Stainless steel stakes. Non-polarizing porous-pot electrodes have
also been tested. Both copper-copper sulfate and lead-lead chloride have been
tested successfully. These can be supplied by the customer or at an additional
cost by Geometrics.
Fig. 5 Stainless steel electrode and cable
6. Ethernet Cables: The Geode EM3D uses a proprietary Ethernet cable that is
specially ruggedized for field use. It also has an isolated “trigger” wire to
synchronize all receiver channels on the network without concern for any delay
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from the Ethernet communication protocol. The cable wiring and connectors
are symmetrical so the connections are reversible.
Fig. 6: Ethernet cable with 10-pad connectors on each end.
7. GPS with cables: Synchronization between the CSAMT transmitter and the
Geode EM3D receivers is through scheduler software using GPS time on the
transmitter and PC Controller. There is only one GPS unit to control all GEM3D
receivers since the GPS connection is to the PC Controller which in turn triggers
the acquisition through the dedicated trigger wire in the Ethernet cable
described above. The GPS used at the writing of this manual is the Global Sat
BU-353S4 Receiver but nearly any good GPS will work.
Fig. 7 GPS receiver with USB cable and GPS antenna (black)
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Chapter 2: Geode EM3D PC Controller setup
The GEM3D Controller is an MS Windows based, ruggedized PC controller designed for
field acquisition work. The controller system consist of the ruggedized PC, an external
GPS with antenna and USB cable and GPS driver software, a Network Interface Box
(NIB), an Ethernet cable to the nearest GEM3D receiver, and the controller software.
a. Ruggedized PC: The Geode EM3D uses a commercial laptop computer
specially adapted for field use operation.
b. GPS: The supplied GPS is used to synchronize the receiver acquisition
to the controlled-source transmitter. It is used as a timing device to
start all the receivers’ acquisition at the same time. The antenna should
be placed at a position that will allow optimal reception for the GPS
satellites. The USB cable functions both to send data from the GPS to
the PC Controller and to provide power from the PC Controller to the
GPS. The bottom left of the GeodEM2010 screen shows the number of
satellites detected by the GPS receiver. In order to function properly
you must lock on to at least three satellites. The number of satellites
detected may vary from GPS receiver to GPS receiver so consult your
GPS operator’s manual.
c. NIB (Network Interface Box): The NIB allows the Ethernet interface
between the GEM3D receiver network and the Ethernet board on the
PC Controller. The toggle switch can be in any of three positions as
follows:
i. Enable Power UP: Pressing the switch to this position will
automatically power up the GEM3D receiver. The startup signal
is on a dedicated line in the Ethernet cable so it does not
require a working Ethernet.
ii. Enable Power Down: This will shut off the GEM3D receivers
when the SAS software is closed.
iii. Plug the Ethernet cable connector from the GEM3D into the
Ethernet connector on the NIB as shown. Next plug the RJ45
connector from the NIB into the Ethernet port on the PC
Controller.
iv. The GEM3D connects to a PC via the Network Interface Box
(NIB; see below). The NIB adapts the digital interface cable to a
standard RJ45 connector, which plugs into the network port on
your PC.
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v.
Figure 8: Network Interface Boxes; single-line (left).
Figure9: Front panel of Network Interface Box.
In addition to being an adaptor, the NIB performs the function of
powering the GEM3D receivers up and down. Refer to the above figure.
Prior to starting SAS, switch to the Enable Power Up position. This will
power up a portion of the acquisition board on the first GEM3D on each
line, enabling them to respond to software commands. The first
GEM3D receiver is the one closest to the acquisition computer in the
array. Upon starting SAS, a start command will be sent to each of these
GEM3D, which will in-turn power up the rest of the GEM3Ds. Once the
software is up and running and all GEM3Ds are recognized, return the
switch to the Enable Power Down position. This will cause all of the
GEM3Ds to shut down when the software is closed.
Note: If you forget to switch to the Enable Power Down position and the
Geodes don’t shut down when you close the software, you can restart
the software, switch to Enable Power Down, and close the software
again.
Test Button
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The Test button:
It powers up the GEM3D for testing purposes. This can be done while
laying out the instrumentation –no connection to the controller PC or
SAS is required. For instance, if you push the Test button on two
adjacent GEM3Ds, a blinking link LED on each unit (see discussion of
blink codes below) will indicate that each unit is receiving link pulses
from the other.
d. Installation of required software onto Controller: All required software
should have been pre-installed on the PC Controller from the
Geometrics factory. The following information is only required if the
software must be re-installed.
e. SAS (System Acquisition Software)
f. GPS software and drivers
g. GeodEM2010
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