Guralp Systems CMG-6TD User Manual
CMG-6TD
Operator's guide
Document No. MAN-T60-0002
Designed and manufactured by
Güralp Systems Limited
3 Midas House, Calleva Park
Aldermaston RG7 8EA
England
Proprietary Notice: The information in this document is
proprietary to Güralp Systems Limited and may be copied or
distributed for educational and academic purposes but may
not be used commercially without permission.
Whilst every effort is made to ensure the accuracy,
completeness or usefulness of the information in the
document, neither Güralp Systems Limited nor any employee
assumes responsibility or is liable for any incidental or
consequential damages resulting from the use of this
document.
Issue F February 2014
CMG-6TD Contents
Table of Contents
1 Preliminary Notes............................................................................................................. 6
1.1 Proprietary Notice......................................................................................................6
1.2 Warnings, Cautions and Notes..................................................................................6
1.3 Manuals and Software...............................................................................................6
1.4 Conventions................................................................................................................ 6
2 Introduction....................................................................................................................... 7
2.1 State of health information........................................................................................8
2.2 Options....................................................................................................................... 8
2.2.1 Storage and interfaces.........................................................................................8
2.2.2 Sensor response.................................................................................................. 8
2.2.3 Wireless networking...........................................................................................8
3 First encounters...............................................................................................................10
3.1 Unpacking and packing........................................................................................... 10
3.1.1 Serial number.................................................................................................... 11
3.2 Test installation........................................................................................................11
3.3 Testing several instruments together.......................................................................13
4 Installing the 6TD........................................................................................................... 17
4.1 Handling notes......................................................................................................... 17
4.2 Connections..............................................................................................................17
4.2.1 The instrument.................................................................................................17
4.2.2 The Break-out box............................................................................................. 18
4.3 Installation notes......................................................................................................19
4.4 Installing in vaults...................................................................................................20
4.5 Installing in pits....................................................................................................... 22
4.6 Other installation methods......................................................................................24
4.7 Rapid installation.....................................................................................................26
4.8 Recovery...................................................................................................................29
4.9 Networking overview...............................................................................................30
4.10 Setting up the Ethernet interface...........................................................................31
4.10.1 Using DeviceInstaller......................................................................................32
4.10.2 Using DHCP....................................................................................................34
4.10.3 Configuration with the Web interface............................................................35
4.11 Setting up wireless networking.............................................................................36
4.11.1 Using DeviceInstaller......................................................................................36
4.11.2 Using DHCP....................................................................................................39
4.11.3 Configuration with the Web interface............................................................39
4.11.4 Installing wireless hardware..........................................................................42
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CMG-6TD
4.12 Configuring the built-in digitizer........................................................................... 42
4.13 Downloading data over FireWire...........................................................................43
4.13.1 Reading 6TD disks..........................................................................................44
4.14 Receiving data in Scream!......................................................................................47
5 Configuration with Scream!...........................................................................................49
5.1 Configuring the digitizer.......................................................................................... 49
5.1.1 System ID..........................................................................................................50
5.1.2 Output control...................................................................................................51
5.1.3 Triggering..........................................................................................................52
5.1.4 Mux Channels................................................................................................... 58
5.1.5 Ports................................................................................................................... 59
5.2 Controlling the instrument......................................................................................60
5.2.1 System............................................................................................................... 61
5.2.2 Triggering..........................................................................................................62
5.2.3 Calibration......................................................................................................... 62
5.2.4 Data flow .......................................................................................................... 63
5.2.5 Transmission mode commands........................................................................65
5.2.6 Buffering mode commands............................................................................... 68
5.3 Digitizer status streams............................................................................................69
5.3.1 GPS....................................................................................................................69
6 Calibrating the 6TD........................................................................................................ 71
6.1 The calibration pack................................................................................................71
6.2 Poles and zeroes.......................................................................................................71
6.3 Frequency response curves......................................................................................73
6.4 Obtaining copies of the calibration pack.................................................................73
6.5 Calibration methods.................................................................................................74
6.5.1 Noise calibration with Scream! .......................................................................74
6.5.2 Sensor response codes......................................................................................77
6.6 The coil constant......................................................................................................78
7 Command-line interface.................................................................................................79
7.1 FORTH......................................................................................................................79
7.2 General configuration..............................................................................................80
7.2.1 SET-ID...............................................................................................................80
7.2.2 BAUD................................................................................................................. 81
7.2.3 LOAD.................................................................................................................81
7.2.4 LOAD-I.............................................................................................................. 81
7.2.5 TEMP?............................................................................................................... 82
7.2.6 ETHER............................................................................................................... 82
7.3 GPS and timing systems...........................................................................................82
7.3.1 GPS-TYPE.......................................................................................................... 82
7.3.2 HR-CYCLE......................................................................................................... 82
7.3.3 XGPS.................................................................................................................83
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CMG-6TD Preliminary Notes
7.3.4 SET-RTC............................................................................................................83
7.3.5 SET-CLOCK.......................................................................................................83
7.3.6 TIME?................................................................................................................84
7.3.7 .FIX....................................................................................................................84
7.3.8 .POSITION........................................................................................................ 84
7.3.9 LEAPSECOND...................................................................................................85
7.3.10 SQPATCH........................................................................................................85
7.4 Output configuration...............................................................................................85
7.4.1 SAMPLES/SEC..................................................................................................85
7.4.2 SET-TAPS.......................................................................................................... 86
7.4.3 COMPRESSION................................................................................................ 87
7.4.4 ETHER............................................................................................................... 87
7.5 Triggering................................................................................................................. 87
7.5.1 TRIGGERS......................................................................................................... 87
7.5.2 TRIGGERED...................................................................................................... 88
7.5.3 STA....................................................................................................................88
7.5.4 LTA....................................................................................................................88
7.5.5 RATIOS.............................................................................................................89
7.5.6 BANDPASS....................................................................................................... 89
7.5.7 PRE-TRIG.......................................................................................................... 89
7.5.8 POST-TRIG........................................................................................................ 90
7.5.9 TRIGGERIN.......................................................................................................90
7.5.10 TRIGGEROUT.................................................................................................90
7.6 Calibration................................................................................................................ 90
7.6.1 SINEWAVE........................................................................................................90
7.6.2 SQUAREWAVE.................................................................................................91
7.6.3 RANDOMCAL................................................................................................... 91
7.6.4 MINUTE............................................................................................................92
7.6.5 %AMPLITUDE..................................................................................................92
7.7 Actions...................................................................................................................... 92
7.7.1 RESP..................................................................................................................92
7.7.2 MASSES?...........................................................................................................92
7.7.3 RE-BOOT...........................................................................................................93
7.8 Flash storage and filing............................................................................................93
7.8.1 SHOW-FLASH..................................................................................................93
7.8.2 DOWNLOAD..................................................................................................... 93
7.8.3 FROM-TIME...................................................................................................... 94
7.8.4 TO-TIME........................................................................................................... 94
7.8.5 ALL-TIMES.......................................................................................................95
7.8.6 ALL-FLASH....................................................................................................... 95
7.8.7 ALL-DATA.........................................................................................................95
7.8.8 STREAM............................................................................................................95
7.8.9 STATUS-ONLY.................................................................................................96
7.8.10 S/S.................................................................................................................... 96
7.8.11 FLUSH............................................................................................................. 96
7.8.12 FLUSHALL...................................................................................................... 96
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CMG-6TD Preliminary Notes
7.8.13 RESET-FLASH.................................................................................................96
7.8.14 ERASEFILE......................................................................................................97
8 Updating the 6TD............................................................................................................98
9 Connector pin-outs........................................................................................................ 100
9.1 Instrument connectors...........................................................................................100
9.1.1 Instrument output port...................................................................................100
9.1.2 Instrument FIREWIRE port.............................................................................101
9.1.3 Instrument ETHERNET port........................................................................... 102
9.2 Breakout box connectors........................................................................................ 103
9.2.1 Breakout box data port....................................................................................103
9.2.2 Breakout box GPS port....................................................................................104
9.2.3 Breakout box power port................................................................................105
10 Specifications.............................................................................................................. 106
11 Revision history.......................................................................................................... 107
12 Appendices..................................................................................................................108
12.1 Key caps................................................................................................................ 108
MAN-T60-0002 5 Issue F - February 2014
CMG-6TD Preliminary Notes
1 Preliminary Notes
1.1 Proprietary Notice
The information in this document is proprietary to Güralp Systems Limited
and may be copied or distributed for educational and academic purposes but
may not be used commercially without permission.
Whilst every effort is made to ensure the accuracy, completeness and
usefulness of the information in the document, neither Güralp Systems
Limited nor any employee assumes responsibility or is liable for any
incidental or consequential damages resulting from the use of this document.
1.2 Warnings, Cautions and Notes
Warnings, cautions and notes are displayed and defined as follows:
1.3 Manuals and Software
All manuals and software referred to in this document are available from the
Güralp Systems website: www.guralp.com unless otherwise stated.
1.4 Conventions
Throughout this manual, examples are given of command-line interactions.
n these examples, a fixed-width typeface will be used:
Example of the fixed-width typeface used.
Commands that you are required to type will be shown in bold:
Example of the fixed-width, bold typeface.
Where data that you type may vary depending on your individual
configuration, such as parameters to commands, these data are additionally
shown in italics:
Example of the fixed-width, bold, italic typeface.
Putting these together into a single example:
System prompt: user input with variable parameters
MAN-T60-0002 6 Issue F - February 2014
Caution: A yellow triangle indicates a chance of damage to or
failure of the equipment if the caution is not heeded.
Note: A blue circle indicates indicates a procedural or advisory
note.
CMG-6TD Introduction
2 Introduction
The CMG-6TD is an ultra-lightweight digital
three-axis seismometer consisting of three
sensors in a sealed case, which can measure
the north/south, east/west and vertical
components of ground motion
simultaneously. Each sensor is sensitive to
ground vibrations over a wide frequency
range (0.033 – 50 Hertz as standard). This
frequency response is made possible by
advanced force-balance feedback
electronics. A built-in 24-bit digitiser
converts ground movements to digital data
at source with maximum fidelity.
The 6TD has a rugged, waterproof design for
ease of installation, and requires no
levelling or centring as long as its base is
within 3 ° from the horizontal. For the best
results, however, you should install where
possible on a hard, near-horizontal surface
well coupled to the bedrock.
Once it is provided with 10 – 28 V power the 6TD will begin operating
automatically, measuring and digitizing ground movements and either
outputting them to your own recording system, or saving them into internal
Flash memory. Accurate timing information can be taken from a GPS unit
connected to the 6TD through a breakout box. Both breakout box and GPS are
normally supplied with the instrument.
Each seismometer is
delivered with a detailed
calibration sheet showing
its serial number,
measured frequency
response in both the long
period and the short period
sections of the seismic
spectrum, sensor DC
calibration levels, and the
transfer function in
poles/zeros notation.
6TD sensors can be delivered in sets of 5 with GPS and cabling included.
Each set is supplied in a “smart” case allowing you to huddle-test the sensors
without needing to unpack them.
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CMG-6TD Introduction
2.1 State of health information
The 6TD constantly monitors the status of the GPS and timing systems,
outputting information in a plain text status stream.
An electronic thermometer also provides regular measurements of the sensor's
internal temperature, which are reported in the same stream. The
thermometer is calibrated to an accuracy up to ± 0.33 °C, with a linearity of
± 0.5 °C.
2.2 Options
2.2.1 Storage and interfaces
The 6TD can be supplied with up to 16 Gb of internal Flash memory for data
storage. The amount you need will depend on the length of your experiment
and the sampling rates used.
You can download data from the internal storage
• over the sensor's standard RS232 data port (compatible with Scream!
and other Güralp data modules),
• over a fast IEEE.1394 (FireWire) link with optional power,
• using an optional “smart” case, over USB from up to five units at once
(see section 3.3 on page 14), or
• if fitted, using the Ethernet interface to transfer data over a local area
network.
2.2.2 Sensor response
The 6TD can be supplied with a response which is flat to velocity from
100 Hertz to any of 1 Hertz, 0.1 Hertz (10 seconds), 0.033 Hertz (30 seconds)
or 0.016 Hertz (60 seconds).
If you do not require high-frequency data, a low-pass digital filter may be
installed at a frequency (below 100 Hertz) that you specify.
2.2.3 Wireless networking
The sensor can be fitted with an optional 802.11b (“Wi-Fi”) wireless interface
in addition to the Ethernet port. This option allows data flow to be
established from autonomous installations with a minimum of setting up.
MAN-T60-0002 8 Issue F - February 2014
CMG-6TD Introduction
For temporary deployments, instruments can be
buried in shallow pits with only the antenna above
ground. You can then contact each station from a
wireless-enabled PC running Scream! without
disturbing the instrument, including monitoring
real-time data and configuring the digitiser.
More permanent arrays also benefit from wireless
technology, particularly in remote areas or where the
terrain makes long cable runs impractical.
For example, stations might be installed with high-gain antennae directed
towards a visible natural feature which is easier to access.
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CMG-6TD Introduction
At this location, which can be up to 500 metres away, a low-power CMG-EAM
data module might act as an access point for the array elements and forward
data onto a higher-bandwidth radio link.
In semi-permanent arrays, a wireless-enabled EAM or laptop PC can be set up
as a temporary access point for the duration of a site visit.
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CMG-6TD First encounters
3 First encounters
3.1 Unpacking and packing
The 6TD seismometer is delivered in a single transportation case. The
packaging is specifically designed for the 6TD and should be reused whenever
you need to transport the sensor. Please note any damage to the packaging
when you receive the equipment, and unpack on a safe, clean surface. For
each instrument in the packaging, you should have received:
• the seismometer;
• the breakout box (which provides separate connections for the signal,
control and power lines);
• a Güralp GPS receiver unit with mounting rod;
• a waterproof IEEE.1394 (FireWire) cable;
• a 15 metre GPS cable, with six-pin bayonet connectors at both ends;
• a power supply cable, with bare wires at one end and a ten-pin bayonet
socket at the other;
• a serial data cable, with a standard nine-pin D connector at one end and
a ten-pin bayonet plug at the other; and
• a calibration and installation sheet.
If you have ordered several instruments with a “smart” case, you can test
them together using power and data distribution units inside the case: see
section 3.3 on page 14.
Assuming all the parts are present, stand the seismometer in the centre of a
bench and identify its external features:
• a handle with North indication,
• a nineteen-way bayonet plug for data, power and GPS signals;
• a six-way bayonet plug for the FireWire interface;
• if fitted, a six-way bayonet plug for the Ethernet interface;
• if fitted, an antenna connector for the Wi-Fi interface;
• a spirit level,
• three feet (two adjustable, and one fixed), and
• two accurate orientation pins (one brass and one steel).
If the Wi-Fi interface is fitted, you will also be supplied with a small aerial for
testing purposes.
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CMG-6TD First encounters
3.1.1 Serial number
The sensor's serial number can be found on the label stuck to the top lid of
the sensor. You should quote this serial number if you need assistance from
Güralp Systems.
3.2 Test installation
This section gives an overview of how to set up a 6TD and begin recording
data. We recommend that you set up a test instrument in your office or
laboratory as a “dry run” to gain a basic understanding of the system and to
check that it is functioning as expected.
This test installation will use the instrument's default settings. Data will be
received using Güralp Systems' Scream! software, available from the website
http://www.guralp.com/
You will need access to a PC with a nine-pin RS232 port, and a 12 V power
source.
1. Install Scream! on your PC and run it.
2. Connect the wire from the breakout box to the 6TD's 19-pin connector.
3. Connect the 6-pin connector on the breakout box to the GPS unit using
the GPS cable. Position the GPS so that it has a good view of the sky.
If you do not have a view of the sky, you can operate the sensor without
a GPS unit, but timing information may be inaccurate.
4. Connect the six-pin data plug on the breakout box to the nine-pin RS232
port on your PC using the serial cable. If your PC does not have a
nine-pin COM port, use an RS232/USB converter. Güralp Systems
recommend converters based on the FTDI chip-set.
5. Use the power cable to connect the ten-pin power plug on the breakout
box to a fused 10 – 28 V power source.
The instrument is now fully operational, and will already be producing
data.
6. After a few seconds you should see the 6TD's digitiser appear under
Network – Local – Com1 in the left-hand panel of Scream!'s main
window. (If your PC has multiple serial ports, it may appear under
some other Com port name.) Soon after, data streams will begin
appearing in the right-hand panel. Streams with higher sample rates
will appear sooner than those with lower sample rates.
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CMG-6TD First encounters
If this does not happen, check all connections, and ensure the power
supply is providing the correct voltage and current.
7. Each data stream has a Stream ID, a six-character string unique to it.
Stream IDs normally identify the instrument, component and sample
rate of each stream. Thus the stream 1026Z2 refers to a Z-component
stream from instrument 1026, at tap 2. For more details on taps and
sample rates, see section 4.1 on page 18.
Data streams ending in 00 are status streams containing state-of-health
information sent from the digitiser.
8. To view data, select a stream and then double-click to open a
Waveview window.
You can view several streams at once by holding down as you
select, and then double-clicking the selection.
9. To start recording new data to a file, right-click on a stream or a
selection of streams and choose Start recording from the pop-up menu.
MAN-T60-0002 13 Issue F - February 2014
CMG-6TD First encounters
Recording settings, directories, etc., can be altered by selecting File →
Setup… from the main menu and switching to the Recording tab.
10. To view status information, select the status stream (the stream with an
ID ending “00”) and right-click to open a pop-up menu. Select View.
The first few status blocks will consist of the 6TD's start-up messages,
including its software revision number and the data streams selected
for downloading and triggering.
Later blocks give information on the GPS system (number of satellites
visible, the location of the GPS antenna, time synchronization status,
etc.) and the baud rates in use for each channel.
3.3 Testing several instruments together
6TD instruments can be ordered in sets of five, with each set delivered in a
single rigid polyurethane transport case.
The sensors are packed so that you can huddle-test the sensors and view data
in Scream! without needing to unpack them. This is done using a power
distribution box and USB and FireWire data hubs built into the case.
MAN-T60-0002 14 Issue F - February 2014
CMG-6TD First encounters
The power and data distribution boxes are located at the front of the case.
The package is shipped with each instrument already connected to these
units, so you can begin testing immediately.
The power supply and combined USB data output cables can be accessed
through a waterproof port on the outside of the case.
To test the instruments:
1. Unscrew the port cover, and pull out the ends of the power and USB
cables.
2. Connect the power cable to your power source, attaching a suitable
connector, if necessary.
MAN-T60-0002 15 Issue F - February 2014
CMG-6TD First encounters
3. Connect the USB data cable to your PC.
The internal Digi EdgePort device should be detected automatically. If
you need drivers, they can be obtained from Digi International's web
site at http://www.digi.com.
4. Install Scream! on your PC and run it.
5. After a few seconds you should see the five instruments appear under
Network → Local → Com1 in the left-hand panel of Scream!'s main
window. (If your PC has multiple serial and USB ports, it may appear
under some other Comn port name.) Soon after, data streams will
begin appearing in the right-hand panel. Streams with higher sample
rates will appear sooner than those with lower sample rates.
If this does not happen, check that the the power supply is providing
the correct voltage.
6. To view data, select the stream or streams of interest and then
double-click to open a WaveView window.
You can also add data streams to an open Waveview window by
dragging a selection onto it from Scream!'s main window.
7. In addition to the power and USB data distribution units, the case
includes a IEEE.1394 (“FireWire”) hub for you to test high speed data
transfer. To do this, connect a FireWire cable from each instrument to
the hub.
Once the instruments are connected, you can access them all through
the FireWire data cable, which is accessible through the waterproof
port in the side of the case.
8. To download all stored data from the array when it is stored in its
transport case, attach a FireWire hard disk to this cable and power up
the array using the power cable from the same port.
MAN-T60-0002 16 Issue F - February 2014
CMG-6TD First encounters
Be sure to allow enough time for all the data to transfer. The 6TD
should be able to transfer data at a sustained rate of around 10 Mb/s, so
a full 8 Gb CMG-6TD instrument should take around 12 minutes to
transfer all its data.
MAN-T60-0002 17 Issue F - February 2014
CMG-6TD Installing the 6TD
4 Installing the 6TD
4.1 Handling notes
Observe the following precautions:
• Do not bump or jolt the sensor when handling or unpacking.
• Do not kink or walk on the data cable (especially on rough surfaces
such as gravel), nor allow it to bear the weight of the sensor.
• Move the instrument with care, and report any sign of loose
components or parts moving inside the instrument to Güralp Systems.
• Do not connect the instrument to power sources except where
instructed.
• Do not ground any of the signal lines from the sensor.
4.2 Connections
4.2.1 The instrument
The 6TD's output connectors are all located on the sensor lid. The sensor can
be supplied with a number of options, so not all the connectors may be
present on your instrument.
All 6TD instruments have a nineteen-pin bayonet connector which carries
power, data and GPS signals. The supplied breakout box (see below) provides
individual connectors for these, or you can make up your own cable if you
prefer.
The 6TD may also have connectors for the FireWire, Ethernet or Wi-Fi
interfaces.
MAN-T60-0002 18 Issue F - February 2014
Caution: Although it has a rugged design, the 6TD is still a sensitive
instrument, and is easily damaged if mishandled. If you are at all
unsure about the handling or installation of the device, you should
contact Güralp Systems for assistance.
Note: All parts of the 6TD are waterproof.
CMG-6TD Installing the 6TD
The connectors for the FireWire and Ethernet options are both six-pin bayonet
plugs. If the labelling has become illegible for any reason, they can be
distinguished by noting that the FireWire connector lies to the East of the
instrument and the Ethernet connector to the North-East, as in the picture
below (which shows an early, unlabelled unit).
4.2.2 The Break-out box
In addition to the cable to the instrument, which is moulded into the case, the
breakout box provides
• a six-pin bayonet socket for connecting the supplied GPS unit;
• a ten-pin bayonet plug for connecting to a PC's serial interface or a
Güralp data module; and
• a six-pin bayonet plug for connecting a 12 V power supply.
You may need to attach a suitable connector to the power cable provided.
The 6TD draws a nominal current of 75 mA from a 12 V supply when in use;
thus, using a 12 V, 25 Ah sealed heavy-duty lead-acid battery, you should
expect the instrument to operate for around a week without recharging.
MAN-T60-0002 19 Issue F - February 2014
CMG-6TD Installing the 6TD
4.3 Installation notes
For the best possible results, a seismometer should be installed on a seismic
pier in a specially-built vault, where conditions are near perfect. Here,
wave-trains arriving at the instrument reflect very well the internal motion of
subsurface rock formations. However, this is not always feasible. For
example,
• instruments may need to be deployed rapidly, perhaps to monitor the
activity of a volcano showing signs of rejuvenation, or to study the
aftershocks of a major earthquake;
• installations may be required in remote locations, or otherwise in
circumstances where it is infeasible to build a vault.
In these situations, the seismometer and its emplacement need to be
considered as a mechanical system, which will have its own vibrational
modes and resonances. These frequencies should be raised as high as
possible so that they do not interfere with true ground motion: ideally, beyond
the range of the instrument. This is done by
• standing the sensor on bedrock where possible, or at least deep in
well-compacted subsoil;
• clearing the floor of the hole of all loose material; and
• using as little extra mass as possible in preparing the chamber.
In temporary installations, environmental factors are also important. The
sensor needs to be well protected against
• fluctuations in temperature,
• turbulent air flow around walls or trees, or around sharp corners or
edges in the immediate vicinity of the sensor;
• vibration caused by heavy machinery (even at a distance), or by
overhead power lines.
This can be done by selecting a suitable site, and placing the instrument in a
protective enclosure. An open-sided box of 5 cm expanded polystyrene slabs,
placed over the instrument and taped down to exclude draughts, makes an
excellent thermal shield.
After installation, the instrument case and mounting surface will slowly
return to the local temperature, and settle in their positions. This will take
around four hours from the time installation is completed.
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CMG-6TD Installing the 6TD
4.4 Installing in vaults
You can install a 6TD in an existing seismic vault with the following
procedure:
1. Unpack the sensors from their container, saving the shipping boxes for
later transportation.
2. Prepare the mounting surface, which should be smooth and free of
cracks. Remove any loose particles or dust, and any pieces of loose
surfacing. This ensures good contact between the instrument's feet and
the surface.
3. If it is not already present, inscribe an accurate North-South line on the
mounting surface.
4. Place the sensor over the scribed line, so that the brass and steel
pointers are aligned with the marked directions, with the brass pointer
facing North. This can be done by rotating the base of the sensor whilst
observing it from above. The brass pointer can be found next to one of
the feet.
If you cannot easily see the pointers, you should align the sensor using
the north arrow on the handle. However, the alignment of the handle
with the sensors inside is less accurate than the metal pointers, so they
should be used wherever possible.
MAN-T60-0002 21 Issue F - February 2014
CMG-6TD Installing the 6TD
5. The top panel of the 6TD includes a spirit level.
Level the sensor using each of the adjustable feet of the instrument in
turn, until the bubble in the spirit level lies entirely within the inner
circle. (The instrument can operate with up to 2 ° of tilt, but with
reduced performance.)
The feet are mounted on screw threads. To adjust the height of a foot,
turn the brass locking nut anticlockwise to loosen it, and rotate the foot
so that it screws either in or out. When you are happy with the height,
tighten the brass locking nut clockwise to secure the foot.
When locked, the nut should be at the bottom of its travel for optimal
noise performance.
6. Connect a 12 V fused power supply to the breakout box.
7. Connect the data cable to a PC. Run Scream!, and check that data are
being produced. Optionally, also check the mass position outputs
(streams ending M8, M9 and MA). These streams are digitized at a slower
rate, and may take up to 15 minutes to appear.
MAN-T60-0002 22 Issue F - February 2014
CMG-6TD Installing the 6TD
8. Cover the instrument with thermal insulation, for example, a 5 cm
expanded polystyrene box. This will shield it from thermal
fluctuations and convection currents in the vault. It also helps to
stratify the air in the seismometer package. Position the thermal
insulation carefully so that it does not touch the sensor package.
9. Ensure that the sensor cable is loose and that it exits the seismometer
enclosure at the base of the instrument. This will prevent vibrations
from being inadvertently transmitted along the cable.
4.5 Installing in pits
For outdoor installations, high-quality results can be obtained by constructing
a seismic pit.
Depending on the time and resources available, this type of installation can
suit all kinds of deployment, from rapid temporary installations to
medium-term telemetered stations.
Ideally, the sensor should rest directly on the bedrock for maximum coupling
to surface movements. However, if bedrock cannot be reached, good results
can be obtained by placing the sensor on a granite pier on a bed of dry sand.
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1. Prepare a hole of 60 – 90 cm depth to compacted subsoil, or down to
the bedrock if possible.
2. On granite or other hard bedrock, use an angle grinder to plane off the
bedrock at the pit bottom so that it is flat and level. Stand the
instrument directly on the bedrock, and go to step 7.
3. On soft bedrock or subsoil, you should install a pier as depicted below.
4. Pour a layer of loose, fine sand into the pit to cover the base. The type
of sand used for children's sand-pits is ideal, since the grains are clean,
dry and within a small size range. On top of the sand, place a smooth,
flat granite plinth around 20 cm across, and shift it to compact the sand
and provide a near-level surface.
Placing a granite plinth on a sand layer increases the contact between
the ground and the plinth, and improves the performance of the
instrument. There is also no need to mix concrete or to wait for it to
set.
5. Alternatively, if time allows and granite is not available, prepare a
concrete mix with sand and fine grit, and pour it into the hole. Agitate
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CMG-6TD Installing the 6TD
(“puddle”) it whilst still liquid, to allow it to flow out and form a level
surface, then leave to set. Follow on from step 7.
Puddled concrete produces a fine-textured, level floor for emplacing
the seismometer. However, once set hard, the concrete does not have
the best possible coupling to the subsoil or bedrock, which has some
leeway to shift or settle beneath it.
6. Alternatively, for the most rapid installation, place loose soil over the
bottom of the pit, and compact it with a flat stone. Place the
seismometer on top of this stone. This method emulates that in step 3,
but can be performed on-site with no additional equipment.
7. Set up the instrument as described in section 4.4 on page 21 (steps 4 to
9).
8. The instrument must now be shielded from air currents and
temperature fluctuations. This is best done by covering it with a
thermal shield.
An open-sided box of five centimetre thick expanded polystyrene slabs is
recommended. If using a seismic plinth on sand (from steps 3–4 or 5),
ensure that the box is firmly placed in the sand, without touching the
plinth at any point. In other installations, tape the box down to the
surface to exclude draughts.
9. Alternatively, if a box is not available, cover the instrument with fine
sand up to the top.
The sand insulates the instrument and protects it from thermal
fluctuations, as well as minimizing unwanted vibration.
10. Ensure that the sensor cable is loose and that it exits the seismometer
enclosure at the base of the instrument. This will prevent vibrations
from being inadvertently transmitted along the cable.
11. Cover the pit with a wooden lid, and back-fill with fresh turf.
4.6 Other installation methods
The recommended installation methods have been extensively tested in a
wide range of situations. However, past practice in seismometer installation
has varied widely.
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Some installations introduce a layer of ceramic tiles between a rock or
concrete plinth and the seismometer (left):
However, noise tests show that this method of installation is significantly
inferior to the same concrete plinth with the tiles removed (right). Horizontal
sensors show shifting due to moisture trapped between the concrete and
tiling, whilst the vertical sensors show pings as the tile settles.
Other installations have been attempted with the instrument encased in
plaster of Paris, or some other hard-setting compound (left):
Again, this method produces inferior bonding to the instrument, and moisture
becomes trapped between the hard surfaces. We recommend the use of fine
dry sand (right) contained in a box if necessary, which can also insulate the
instrument against convection currents and temperature changes. Sand has
the further advantage of being very easy to install, requiring no preparation.
Finally, many pit installations have a large space
around the seismometer, covered with a wooden roof.
Large air-filled cavities are susceptible to currents
which produce lower-frequency vibrations, and sharp
edges and corners can give rise to turbulence. We
recommend that a wooden box is placed around the
sensor to protect it from these currents. Once in the
box, the emplacement may be backfilled with fresh
turf to insulate it from vibrations at the surface, or
simply roofed as before.
By following these guidelines, you will ensure that
your seismic installation is ready to produce the
highest quality data.
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4.7 Rapid installation
The 6TD is specially designed for rapid installation, and may be fully
installed in a few hours. This section details a method of deploying 6TD
instruments with the minimum of additional equipment. This is
recommended for situations where seismic instrumentation needs to be
installed very quickly, e.g. to study a resumption of volcanic activity, or where
difficulty of access to the site prevents you from constructing a full seismic
pit. You should always construct a pit if possible (see section 4.5 on page 23),
since the data produced will be of significantly higher quality.
1. Prepare a hole of 60 – 90 cm depth to compacted subsoil, or down to
the bedrock if possible.
2. Clean the hole down to the bottom, and remove any loose material from
the mouth. Ensure that the bottom of the hole is relatively flat.
3. If the bottom of the hole is made of hard rock, you may need to put in
some loose sand or soil so that the sensor can be levelled.
4. Connect the sensor to cables for the GPS unit and power source. If
your 6TD has the Wi-Fi option, connect your antenna to the sensor.
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5. Carefully insert the instrument into the hole, protected by a tough
plastic bag to keep water out. Use a bag strong enough to bear the
weight of the sensor and breakout box, so that it can be recovered
easily.
6. Press the sensor down firmly into the soil, without tapping or hitting it.
7. Check the bubble level on top of the instrument package.
Adjust the instrument's position if necessary so that the bubble lies
entirely within the black circle.
8. Pack soil or sand around the instrument to hold it steady. Make sure
the soil or sand is firmly compacted and not at all loose.
9. Re-check the bubble level. If you cannot adjust the soil packing at this
stage and the sensor is not level, you will need to clear the hole and
restart from step 3.
10. Place the breakout box and any excess cable on top of the sensor, inside
the plastic bag.
11. Group the cables coming from the bag for a distance of about 1 m, and
keep them together with insulating tape.
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12. Tie the top of the package and fold it over so that water cannot get in.
Leave any excess cable within the bag.
13. Cover the installation with soil or sand until it is no longer visible.
14. Attach a GPS unit to the cable coming from the sensor. Position it so
that it has a good view of the sky.
If possible, place the GPS near the instrument so that it can be found
more easily.
15. If you are installing a 6TD with Wi-Fi, connect and install the antenna.
16. Bury the cables so that they cannot be seen.
17. If you are using a battery as a power source, dig a second hole for it.
This hole does not need to be as deep as the pit for the instrument—
perhaps 10 cm plus the height of the battery.
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18. Attach the sensor power cable to the battery, and wrap it in another
plastic bag. Place the bag in the hole.
19. Tie the bag and fold over, to make the battery as waterproof as possible.
20. Bury the power cable between the battery and the instrument, and
compact soil or sand around the bag.
21. Fill in and cover the hole so that it is not visible.
4.8 Recovery
Care should be taken when recovering the 6TD, since tapping or banging it
can cause damage to the sensors inside. The following instructions assume
that you have installed the instrument following the steps above.
1. Find the GPS receiver, which will be the only feature visible from the
surface, and follow the buried data cable from it to the instrument.
2. Carefully remove earth from the hole until you find the power cable
coming from the instrument.
3. Follow the power cable to the battery pit, and carefully dig away the
soil to reveal the battery about 10 cm from the surface.
4. Disconnect the power cable from the battery. (With the power off, the
sensor is less likely to suffer electrical damage during recovery.)
5. Return to the location of the sensor, and dig down to it. You should be
able to remove a spade's head depth of soil without hitting the
instrument. Beyond that, using a small hand shovel, follow the wires
and carefully remove the remaining soil until you can see the plastic
bag. Take special care not to damage the wires, which should be tied
together in the vicinity of the bag.
6. Carry on removing soil, either with your hands or (very carefully!) with
the shovel, until the whole bag is uncovered to about half the height of
the instrument.
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