Guralp Systems CMG-3ESPCD User Manual
CMG-3ESPCD
Digital Broadband Seismometer
Technical Manual
Document No. MAN-C3E-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 B November 2013
CMG-3ESPCD Digital Broadband Seismometer Contents
Table of Contents
1 Preliminary Notes............................................................................................................. 5
1.1 Proprietary Notice......................................................................................................5
1.2 Warnings, Cautions and Notes.................................................................................. 5
1.3 Manuals and Software...............................................................................................5
1.4 Conventions................................................................................................................ 5
2 Introduction....................................................................................................................... 6
2.1 Sensor response.......................................................................................................... 7
3 Installing the 3ESPCD....................................................................................................... 8
3.1 First encounters.......................................................................................................... 8
3.1.1 Unpacking........................................................................................................... 8
3.1.2 Serial number...................................................................................................... 8
3.1.3 Handling notes.................................................................................................... 8
3.1.4 Connections........................................................................................................9
3.1.5 FireWire............................................................................................................... 9
3.1.6 Power supply.....................................................................................................10
3.2 Installation notes...................................................................................................... 10
3.3 Installing in vaults................................................................................................... 11
3.4 Installing in pits....................................................................................................... 14
3.5 Other installation methods...................................................................................... 16
3.6 Rapid installation.....................................................................................................18
3.6.1 Deployment.......................................................................................................18
3.6.2 Recovery............................................................................................................ 21
3.7 Installing in post-holes.............................................................................................22
3.8 Using the 3ESPCD....................................................................................................23
3.8.1 Retrieving data.................................................................................................. 23
3.8.2 Reading digitiser disks......................................................................................24
4 Calibrating the 3ESPCD.................................................................................................. 28
4.1 The calibration pack................................................................................................ 28
4.1.1 Poles and zeroes................................................................................................28
4.1.2 Frequency response curves...............................................................................29
4.1.3 Obtaining copies of the calibration pack.........................................................32
4.2 Calibration methods.................................................................................................32
4.3 Calibration with Scream!.........................................................................................33
4.3.1 Sensor response codes .....................................................................................37
4.4 The coil constant...................................................................................................... 37
5 Using Scream!................................................................................................................. 39
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CMG-3ESPCD Digital Broadband Seismometer
5.1 Configuring digitisers...............................................................................................39
5.1.1 System ID..........................................................................................................40
5.1.2 Output control...................................................................................................41
5.1.3 Triggering.......................................................................................................... 44
5.1.4 Mux Channels...................................................................................................51
5.1.5 Ports................................................................................................................... 51
5.2 Controlling digitisers................................................................................................ 53
5.2.1 System............................................................................................................... 53
5.2.2 Triggering.......................................................................................................... 54
5.2.3 Calibration......................................................................................................... 54
5.2.4 Mass Control.....................................................................................................54
5.2.5 Data flow........................................................................................................... 55
6 Command line interface................................................................................................. 60
6.1 Introduction.............................................................................................................. 60
6.1.1 FORTH............................................................................................................... 60
6.2 General configuration..............................................................................................61
6.2.1 SET-ID............................................................................................................... 61
6.2.2 SENSOR-TYPE..................................................................................................61
6.2.3 GPS-TYPE.......................................................................................................... 61
6.2.4 BAUD.................................................................................................................62
6.2.5 AZIMUTH......................................................................................................... 62
6.2.6 CROSS............................................................................................................... 63
6.3 Output configuration...............................................................................................63
6.3.1 SAMPLES/SEC..................................................................................................63
6.3.2 CONTINUOUS.................................................................................................. 64
6.3.3 SET-TAPS.......................................................................................................... 64
6.4 Triggering................................................................................................................. 65
6.4.1 TRIGGERS......................................................................................................... 65
6.4.2 TRIGGERED...................................................................................................... 65
6.4.3 STA.................................................................................................................... 65
6.4.4 LTA....................................................................................................................66
6.4.5 RATIOS.............................................................................................................66
6.4.6 PRE-TRIG.......................................................................................................... 66
6.4.7 POST-TRIG........................................................................................................66
6.4.8 TRIGGERIN....................................................................................................... 67
6.4.9 TRIGGEROUT................................................................................................... 67
6.5 Calibration................................................................................................................ 67
6.5.1 SINEWAVE........................................................................................................67
6.5.2 SQUAREWAVE.................................................................................................68
6.5.3 RANDOMCAL...................................................................................................68
6.5.4 MINUTE............................................................................................................69
6.5.5 %AMPLITUDE.................................................................................................. 70
6.6 Actions...................................................................................................................... 70
6.6.1 LOCK................................................................................................................. 70
6.6.2 UNLOCK............................................................................................................ 70
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6.6.3 CENTRE.............................................................................................................70
6.6.4 RE-BOOT........................................................................................................... 71
6.7 Data storage and recovery........................................................................................71
6.7.1 SHOW-FLASH.................................................................................................. 71
6.7.2 DIRECT.............................................................................................................. 72
6.7.3 FILING............................................................................................................... 72
6.7.4 ADAPTIVE........................................................................................................ 72
6.7.5 FIFO...................................................................................................................72
6.7.6 DOWNLOAD..................................................................................................... 73
6.7.7 ALL-FLASH....................................................................................................... 73
6.7.8 ALL-DATA......................................................................................................... 73
6.7.9 STREAM............................................................................................................ 73
6.7.10 STATUS-ONLY...............................................................................................74
6.7.11 S/S.................................................................................................................... 74
6.7.12 ALL-TIMES.....................................................................................................74
6.7.13 FROM-TIME.................................................................................................... 74
6.7.14 TO-TIME......................................................................................................... 74
6.7.15 GO.................................................................................................................... 75
6.7.16 END-DOWNLOAD.......................................................................................... 75
6.7.17 DISKMENU..................................................................................................... 75
6.7.18 MBTRANSFER................................................................................................76
6.7.19 ERASEFILE...................................................................................................... 76
7 Inside the 3ESPCD.......................................................................................................... 77
7.1 Inside the 3ESPCD................................................................................................... 77
7.1.1 The sensors.......................................................................................................77
7.1.2 The control system............................................................................................ 77
7.1.3 The feedback system.........................................................................................81
7.2 Inside the DM24.......................................................................................................85
7.2.1 Architecture...................................................................................................... 85
7.2.2 Updating firmware with an EAM.....................................................................87
7.2.3 Updating firmware with Scream!.....................................................................87
8 Appendix A - Connector pin-outs................................................................................... 90
8.1 GPS port.................................................................................................................... 90
8.2 DATA OUT port....................................................................................................... 91
8.3 FIREWIRE port.........................................................................................................92
8.4 AUXILIARY port (optional).....................................................................................93
9 Appendix B - Sensor Specifications............................................................................... 94
10 Appendix C - Digitiser specifications..........................................................................95
11 Revision History............................................................................................................ 97
MAN-C3E-0002 4 Issue B - November 2013
CMG-3ESPCD Digital Broadband Seismometer 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.
In 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
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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-3ESPCD Digital Broadband Seismometer Introduction
2 Introduction
The CMG-3ESPCD is a full-featured three-axis digital seismometer consisting
of three sensors in an ultra-lightweight case, which can measure the
north/south, east/west and vertical components of ground motion
simultaneously, and a built-in DM24 digitiser.
Each sensor is sensitive to ground vibrations in the frequency range 0.003 Hz
to 50 Hz, a broadband frequency response made possible by advanced
force-balance feedback electronics. Because of this wide response range, the
3ESPCD can replace many of the instruments conventionally used in a
seismic observatory; it also produces true pulse-shape records suitable for
modern earthquake mechanism analysis. Its small size and low weight make
it an ideal choice for rapid deployment of low-noise installations.
The 3ESPCD will produce the best results if it is mounted on a hard,
near-horizontal surface well coupled to the bedrock. After levelling and
orienting the case, you can perform accurate adjustments internally by
sending the instrument control signals. These electronics allow it to
compensate for a tilt of up to 3° from horizontal.
The seismometer unit is self-contained apart from its 12 V power supply.
Once levelled and centred, it will begin operating automatically. Its output is
digitised within the sensor by the internal DM24 digitiser, which provides
data streams in GCF format. The instrument can be connected to a PC's serial
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CMG-3ESPCD Digital Broadband Seismometer Introduction
port or to a Güralp Systems data module using the cable supplied. The
digitiser also controls the instrument's centring and mass locking processes.
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.
2.1 Sensor response
The 3ESPCD can be supplied with a response which is flat to velocity from
100 Hz to any of 0.1 Hz (10 s), 0.033 Hz (30 s), 0.016 Hz (60 s), 0.01 Hz (100 s)
or 0.0083 Hz (120 s). Alternatively, a hybrid response function may be
provided. See section 7.1.1 on page 77 for more details.
If you do not require high-frequency data, a low-pass filter may be installed at
a frequency (below 100 Hz) that you specify.
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CMG-3ESPCD Digital Broadband Seismometer Installing the 3ESPCD
3 Installing the 3ESPCD
3.1 First encounters
3.1.1 Unpacking
The 3ESPCD seismometer is delivered in a single transportation case. The
packaging is specifically designed for the 3ESPCD 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. The package should contain:
• the seismometer;
• a GPS unit, if ordered, with cable;
• a 10-pin connector for your power/data lead (see below); and
• a calibration and installation sheet.
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,
• DATA OUT and GPS connectors;
• a mil-spec FireWire connector;
• other optional connectors as ordered;
• a bubble level,
• an air vent port,
• two adjustable feet, and
• two accurate orientation pins (one brass and one steel).
3.1.2 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.
3.1.3 Handling notes
The 3ESPCD is 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.
• Avoid bumping or jolting any part of the sensor when handling or
unpacking.
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• 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.
• Do not connect the instrument to power sources except where
instructed.
• Do not ground any of the signal lines from the sensor.
• Avoid moving the instrument whilst the masses are unlocked. The
3ESPCD is designed to tolerate a certain amount of motion with the
sensor masses unlocked, e.g. over short distances carried by hand. For
example, if the remote locking procedure fails, removing the
instrument for diagnostics is unlikely to damage it. However, you
should always lock the sensor masses before shipping or transporting
the sensor over longer distances.
3.1.4 Connections
The instrument has the following connectors:
• The DATA OUT connector outputs RS232 data to your PC or data
module, and also provides power to the instrument.
• The GPS connector is intended for connection to a Güralp GPS module.
• The FIREWIRE connector can be attached to any IEEE.1394 (FireWire)
hard disk or data storage unit using the cable provided.
3.1.5 FireWire
The digitiser has an IEEE.1394 (“FireWire”) port, which you can use to
download data onto a compatible hard disk.
Before you can use the disk, you will need to erase/format it. The digitiser
saves data on the hard disk in raw mode, so you cannot use a PC's standard
software to reset the disk.
To erase/format a FireWire disk for use with the digitiser:
1. Power up the digitiser, and connect it to your computer's serial port.
2. Open its terminal console. To do this using Güralp Systems' Scream!
software, right-click on the digitiser's icon (once it appears) and select
Terminal.... From a Güralp EAM, issue the command
data-terminal
and select the appropriate data source from the menu
3. Issue the command DISKMENU. You will see the message
Plug in FireWire cable
4. Plug in your disk. The digitiser will display information about the disk
as soon as it is detected.
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CMG-3ESPCD Digital Broadband Seismometer Installing the 3ESPCD
5. Within the next seven seconds, press any key to bring up the disk menu.
6. Key to reset the disk.
7. When the reset is complete, remove the disk.
You will now be able to download data onto the disk when required.
3.1.6 Power supply
The sensor requires a 12 V power supply, which it obtains through the DATA
OUT port. You may wish to terminate the supplied power cable in order to
connect a 12 V power source to this connector: it is supplied with bare ends.
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.
A power management module can be installed as an option, which allows the
3ESPCD to operate from a 10 – 15 V supply range. This module also cuts the
input power to the sensor electronics if it drops below 10.5 V, to minimize
discharge from battery-operated installations.
The 3ESPCD draws a nominal current of 200 mA from a 12 V supply when in
use. During locking and unlocking of the sensor masses, this current rises
briefly to 750 mA. It is recommended that you carry a spare 12 V battery
when visiting an installation for maintenance, in case the sensor needs to be
moved and the on-site batteries no longer have sufficient charge to perform
the locking procedure.
3.2 Installation notes
The goal of any seismic installation is to ensure that wave-trains arriving at
the instrument accurately reflect the internal motion of subsurface rock
formations. To achieve this, 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.
In particular, the sensor needs to be protected against environmental factors
such as
• 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 equipment in or near the installation, particularly
computer equipment; and
• vibration caused by heavy machinery (even at a distance), or by
overhead power lines.
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In seismic vaults, instruments are often installed on piers. It is important to
ensure that the interface between the pier and the floor does not introduce
noise, and that the pier itself does not have resonant frequencies within the
passband. Ideally, a seismic pier will be significantly wider than it is high (to
minimize flexing) and will form a single piece with the floor, e.g. by moulding
a poured concrete floor with a wooden frame.
Many situations do not allow for the construction of a seismic vault. For
example, you may need to deploy quickly to monitor the activity of a volcano
showing signs of rejuvenation, or to study the aftershocks of a major
earthquake; or the site itself may be too remote to ship in construction
equipment.
Temporary installations can be protected against spurious vibrations by
• selecting a suitable site,
• 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),
• 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.
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. If you require
long-period recording, you should re-zero the instrument after this time.
3.3 Installing in vaults
You can install a 3ESPCD in an existing seismic vault with the following
procedure:
1. Unpack the sensor from its container, saving the shipping box 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
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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.
5. The top panel of the 3ESPCD 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.
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6. Plug the grey/blue power/data cable into the ten-pin connector on the
instrument's lid and connect a 12 V power supply to the ends of the
grey cable. Connect the DE9 connector to a PC running scream, using a
USB-to-RS232 converter, if required.
Alternatively, connect the ten-pin connector on the instrument's lid to a
CMG-EAM using cable CAS-DCM-0001 (green).
7. Plug in the GPS cable and connect the GPS receiver.
8. In Scream's set-up dialogue, select the “COM Ports” tab and set the
Baud rate of the appropriate COM port to 38,400 Baud. Click OK and
wait for the instrument to appear in Scream's source tree.
Right-click on the digitiser's entry in the source tree and select
Control.... Click on the Mass control tab, followed by Unlock. (If the
Mass control tab is unavailable, check the sensor type in the Sensor
type tab, apply, and open a new Control window.)
Alternatively, if you are using an EAM, navigate to the Control →
Instruments Port X Instrument... page and click on the Unlock→
instrument button.
9. Right-click on the digitiser's entry in Scream's source tree and select
Control.... Click on the Mass control tab, followed by Centre.
Alternatively, if you are using an EAM, navigate to the Control →
Instruments Port X Instrument... page and click on the centre button.→
Monitor the mass positions during the centring operation. You may
need to initiate several rounds of centring before the mass positions
reach an acceptable value.
10. 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
MAN-C3E-0002 13 Issue B - November 2013
Note: GSL strongly recommend USB/RS232 convertors
based on the FTDI chipset. Numerous problems have been
found with convertors based on the other common chip-set.
Caution: After this point, you should be careful not to tilt
the instrument or you may damage it.
CMG-3ESPCD Digital Broadband Seismometer Installing the 3ESPCD
stratify the air in the seismometer package. Position the thermal
insulation carefully so that it does not touch the sensor package.
11. Ensure that the cables are loose and that they exit the seismometer
enclosure at the base of the instrument. This will prevent vibrations
from being inadvertently transmitted along the cables.
3.4 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.
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.
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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, as in step 4.
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
(“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
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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 3.3 on page 11.
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 5 cm 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.
3.5 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.
Some installations introduce a layer of ceramic tiles between a rock or
concrete plinth and the seismometer, as shown in the left-hand picture below:
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.
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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. The emplacement may then 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.
3.6 Rapid installation
This section details a method of deploying 3ESPCD 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 3.4 on page 14), since the data
produced will be of significantly higher quality.
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3.6.1 Deployment
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.
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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. Recheck 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. Power the sensor and connect it to a laptop. Unlock the masses using
Scream's Control window.
11. Place the breakout box and any excess cable on top of the sensor, inside
the plastic bag.
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CMG-3ESPCD Digital Broadband Seismometer Installing the 3ESPCD
12. Group the cables coming from the bag for a distance of about 1 m, and
keep them together with insulating tape.
13. Tie the top of the package and fold it over so that water cannot get in.
Leave any excess cable within the bag.
14. Cover the installation with soil or sand until it is no longer visible.
15. Attach a GPS unit to the cable coming from the sensor. Seal the
connection between the data cable and the GPS unit's IEEE 1394 cable
inside a plastic bag to protect it from moisture.
16. Position the GPS unit so that it has a good view of the sky. Bury the
cable and connector package so that they cannot be seen.
17. If possible, place the GPS near the instrument so that it can be found
more easily, and the connector package near the GPS so you can
retrieve data from the instrument without affecting the installation.
18. 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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CMG-3ESPCD Digital Broadband Seismometer Installing the 3ESPCD
19. Attach the sensor power cable to the battery, and wrap it in another
plastic bag. Place the bag in the hole.
20. Tie the bag and fold over, to make the battery as waterproof as possible.
21. Bury the power cable between the battery and the instrument, and
compact soil or sand around the bag.
22. Fill in and cover the hole so that it is not visible.
3.6.2 Recovery
Care should be taken when recovering the 3ESPCD, 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. Connect a laptop to the data connector and, using Scream's Control
dialogue, lock the masses.
5. Disconnect the power cable from the battery. (With the power off, the
sensor is less likely to suffer electrical damage during recovery.)
6. 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.
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7. 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.
8. If the hole is relatively dry, open the bag and lift the instrument out by
its handle.
9. Alternatively, if the hole is waterlogged, carefully lift out the entire bag
in one piece, and remove the contents at the surface.
3.7 Installing in post-holes
The 3ESPCD is suitable for installation in potholes. In soft subsoil, a hole 2 –
4 metres deep and 20 cm wide can be conveniently excavated using a
tractor-mounted or hand-operated pothole auger. To minimize surface effects,
you should ensure that the hole is at least 1 metre deeper than the length of
the instrument, and preferably somewhat more.
Since the hole has no lining, it may occasionally flood. However, most soil
types are sufficiently permeable to allow water to soak away, leaving the
packing material moist.
To install a 3ESPCD in a pothole:
1. Clean the pothole, making sure there is no loose material around the
mouth of the hole or on its base.
2. Prepare the instrument package, making sure the inclinometer is
visible, and attach it to a winch or hoist by clamping a light steel cable
to the centre of the handle so that the package hangs vertically.
Connect the signal cable to the instrument.
3. Add packing material to the hole to about 15 cm depth. Fine crushed
rock, with a high proportion of rock flour and fine particles, makes
excellent packing material. Alternatively, a mixture of 3 mm grade
angular coarse grit with around 30% medium grit gives good results.
Moisten the packing material in the hole and ram firm.
4. Lower the instrument to the bottom of the hole, but without slackening
the lifting cable.
5. Fill more packing material around the instrument for about 30 cm,
moisten, and ram firm.
6. Use the bubble level to check that the instrument remains within its tilt
tolerance (± 2 °).
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Caution: Do not lift the instrument by any of the attached
cables. Straining the cables may result in invisible damage,
making future installations unreliable.
CMG-3ESPCD Digital Broadband Seismometer Installing the 3ESPCD
7. Continue filling, moistening and packing until the instrument is
buried, checking that the tilt remains within tolerance.
8. Release the strain on the lifting cable, and allow the packing material to
settle for 24 hours.
9. If all is well after the settling period, release the lifting tackle, coil a tail
of the lifting wire into the top of the hole and backfill almost to the
surface.
10. Ensure that the signal cable is slack, and fix it to a support at the top of
the hole.
11. Ram a split wooden bung into the top of the hole, and cover with
sandbags.
12. Attach the signal cable to your laptop. Power the sensor, and unlock it.
Carry out preliminary tests using Scream!, if required.
3.8 Using the 3ESPCD
Once the 3ESPCD is powered, it will start producing data immediately. You
can now start configuring it for your own needs. There are three ways you
can do this:
• using the graphical interface provided by Scream! (see section 5 on page
39);
• using the web interface of a CMG-EAM (see MAN-EAM-0003); or
• over a terminal connection (see section 6 on page 60).
All three methods provide full access to the configuration options of the
digitiser.
3.8.1 Retrieving data
You can configure the digitiser to operate in a number of transmission modes.
These modes determine whether the unit stores data in its on-board Flash
memory, sends it over the serial link in GCF format, or does some
combination of these. See “Data flow ” in Section 5.2.5 on page 55 for more
details.
If you choose a transmission mode where some data are stored in Flash
memory, you will need to recover this data at a later date. You can do this
either over the serial link, or using the digitiser's FireWire interface.
To download data over FireWire, simply plug the disk in. If there are enough
new data waiting to be transferred (by default 128 Mb), they will immediately
be downloaded onto the disk. The internal pointers will be updated to mark
the data as downloaded.
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Alternatively, for more downloading options, issue the command DISKMENU
from the digitiser's console before attaching the disk. See Section 6.7 on page
71 for more information. You can use DISKMENU to download any section of
data, whether or not it has already been transferred.
While the FireWire interface is active, it will consume about 200 mA of power
(from a 12 V supply). If you interrupt a transfer whilst in progress, the
digitiser will re-boot, but the data held in memory will not be affected.
To download data over the serial link:
1. Open the digitiser's console. To do this using Güralp Systems' Scream!
software, right-click on the digitiser's icon (once it appears) and select
Terminal....
Alternatively, from a Güralp EAM, issue the command
data-terminal
2. If you want to download all data held in the Flash memory, issue the
command
ALL-FLASH ALL-DATA DOWNLOAD
3. Alternatively, select a particular set of streams, sample rates and times
to download using the STREAM, S/S, FROM-TIME and TO-TIME
commands, and finish with DOWNLOAD. See Section 6.7 on page 71 for
more information.
4. Close the terminal session. If you are using Scream! or an EAM, the
digitiser should start transmitting immediately. Otherwise, you may
need to issue the command GO to start transferring data.
3.8.2 Reading digitiser disks
The digitiser uses a special disk format, DFD, for recording data. You can
read this data into a PC using Scream! or the GCFXtract utility, which is freely
available from the Güralp Systems Web site.
Güralp Systems can provide fully-tested disks with FireWire and USB
connectors. Alternatively, a third-party FireWire disk may be used (although
compatibility is not guaranteed.)
3.8.2.1 Reading disks with GCFXtract
To read a disk using GCFXtract:
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Note: The DFD format is not the same as that used by the Güralp
Systems EAM data modules, which use a FAT32-compatible or extn
journalling file system.
CMG-3ESPCD Digital Broadband Seismometer Installing the 3ESPCD
1. Attach the disk to your computer. You can use FireWire, USB, or any
other interface supported by your computer and the disk.
2. Start GCFXtract
The following screen is displayed:
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Caution: Some operating systems, not recognising the DFD
format, will offer to re-format the disk when it is attached.
Always say NO: reformatting the disk will make the recorded
data unreachable and may over-write some of it. If you
accidentally allow the operating system to format a drive
containing valuable recorded seismic data, please contact
support@guralp.com for help.
Note: As GCFXtract requires raw disk device access, it must
be run with elevated privileges. On Windows 7 and
Windows Vista, it needs to “Run as Adminsitrator”. On
Windows XP, you need to be logged in as administrator. On
Linux, you need to run as root, or a user with read/write
permissions for raw disk devices. On most Linux systems,
you can grant these permissions with the command
sudo adduser user_name disk
CMG-3ESPCD Digital Broadband Seismometer Installing the 3ESPCD
The program will first search for non-DOS disks on all the interfaces it
understands. If it does not find your disk, check that it is properly
connected and that any relevant drivers have been installed, then click
the button.
3. When you start up GCFXtract, the program searches all SCSI interfaces
and devices for DM24-format disk drives. The ID of each disk is
displayed in the drop-down list at the top of the window. Under each
disk, GCFXtract lists the transfer sessions it has found on the disk. The
DM24 creates a new transfer session each time it saves data to the disk.
You can extract data either from a single transfer session, or from the
entire disk.
4. Select the required disk or transfer session from the drop-down list, and
click . GCFXtract will scan the disk and display all the streams it
finds in the selection area below. For each stream, the Stream ID and the
number of blocks found are shown. This operation requires roughly
12 Mb of available memory for every Gb of space on the disk. If you
have a very large disk, your computer may have to use its hard disk to
make enough space. This will slow down scanning considerably.
5. By default, all streams containing more than 100 blocks are selected for
extraction. You can change which streams to extract by ticking or
clearing the check-box beside each stream. You can tick or clear all of the
boxes using the and buttons. Clicking ticks all cleared
boxes, and clears all ticked boxes.
6. Enter a path name into the Target Directory field, or use the
button to find a directory. This will be used as the root directory for
extracted data. If it does not exist, GCFXtract will create it.
7. Enter a format string into the Filename Format field. The syntax is the
same as the format string in Scream! and full documentation is available
by pressing the button beside the format entry field in interactive
mode.
8. Normally, GCFXtract outputs GCF files, to ensure all the information in
the original data are retained. If you want to convert to a different
format, select it from the Output Data Format drop-down box.
GCFXtract can output in most of the formats supported by Scream!.
9. Data are automatically placed in time order and saved in multiple files,
each file containing a contiguous segment of data. By default, data
streams are recorded in files 60 minutes long. To change this to some
other number of minutes, alter the value in the Data File Duration (mins)
box. For data streams, if there is a gap in the data, GCFXtract will start a
new file anyway.
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CMG-3ESPCD Digital Broadband Seismometer Installing the 3ESPCD
10. Status streams are also saved in multiple files, but have a default length
of 24 hours. To change this, alter the value under Status File Duration
(hours).
11. When you are happy with the settings, click to begin extracting
the data.
12. Clicking sets a flag on the disk which marks it as empty. Next
time a digitiser wants to transfer data, it will begin at the beginning of
the disk, overwriting the old data. When this happens, none of the old
data can be extracted with GCFXtract. Until then, however, you will still
be able to retrieve all the data.
3.8.2.2 Reading disks with Scream!
You can also read disks with Scream!. This allows you to view data in the
process of being transferred, but is slightly slower, because Scream! does not
read data in strict order. To read a disk with Scream!:
1. Attach the disk to your computer. You can use FireWire, USB, or any
other interface supported by your computer and the disk.
2. Run Scream!, and select File Setup... from the main menu. Select the →
Files tab.
3. Set the Base Directory, Filename Format and Data Format as required.
Also, if required, set the Post-processor and Granularity options to your
preference. Consult the Scream! documentation for details.
4. Select the Recording tab, and tick the Auto Record—Enable for Data
Streams and Auto Record—Enable for Status Streams check-boxes. Click
OK. Scream! will remember the recording options you set in steps 3 and
4 for later occasions.
5. Select File Read SCSI disk... from the main menu. Scream! will search →
for attached disks, and open a window with a list of all the streams it has
found.
6. Select the streams you want to replay, and click Open. The disk will
appear in the left-hand pane of Scream!'s main window, and the streams
you have selected will start playing into the stream buffer, as well as
being recorded.
7. When you have finished transferring the data, if you want to reset the
disk, select File Reset SCSI disk... from Scream!'s main menu. Select →
the disk you want to reset, and click OK.
More information is contained in the Scream! Manual, MAN-SWA-0001.
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CMG-3ESPCD Digital Broadband Seismometer Calibrating the 3ESPCD
4 Calibrating the 3ESPCD
4.1 The calibration pack
All Güralp sensors are fully calibrated before they leave the factory. Both
absolute and relative calibration calculations are carried out. The results are
given in the calibration pack supplied with each instrument:
• Works Order : The Güralp factory order number including the
instrument, used internally to file details of the sensor's manufacture.
• Serial Number: The serial number of the instrument
• Date: The date the instrument was tested at the factory.
• Tested By: The name of the testing engineer.
There follows a table showing important calibration information for each
component of the instrument, VERTICAL, NORTH/SOUTH, and EAST/WEST.
Each row details:
• Velocity Output (Differential) : The sensitivity of each component to
velocity at 1 Hz, in volts per m/s. Because the 3ESPCD uses balanced
differential outputs, the signal strength as measured between the +ve
and –ve lines will be twice the true sensitivity of the instrument. To
remind you of this, the sensitivities are given as 2 × (single-ended
sensitivity) in each case.
• Mass Position Output : The sensitivity of the mass position outputs to
acceleration, in volts per ms-2. These outputs are single-ended and
referenced to signal ground.
• Feedback Coil Constant : A constant describing the characteristics of
the feedback system. You will need this constant, given in amperes per
ms-2, if you want to perform your own calibration calculations (see
below.)
• Power Consumption : The average power consumption of the sensor
during testing, given in amperes and assuming a 12 V supply.
• Calibration Resistor : The value of the resistor in the calibration
circuit. You will need this value if you want to perform your own
calibration calculations (see below.)
4.1.1 Poles and zeroes
Most users of seismometers find it convenient to consider the sensor as a
“black box”, which produces an output signal V from a measured input x. So
long as the relationship between V and x is known, the details of the internal
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CMG-3ESPCD Digital Broadband Seismometer Calibrating the 3ESPCD
mechanics and electronics can be disregarded. This relationship, given in
terms of the Laplace variable s, takes the form
( V / x ) (s) = G × A × H (s)
In this equation
• G is the acceleration output sensitivity (gain constant) of the
instrument. This relates the actual output to the desired input over the
flat portion of the frequency response.
• A is a constant which is evaluated so that A × H (s) is dimensionless
and has a value of 1 over the flat portion of the frequency response. In
practice, it is possible to design a system transfer function with a very
wide-range flat frequency response.
The normalising constant A is calculated at a normalising frequency
value fm = 1 Hz, with s = j fm, where j = √–1.
• H (s) is the transfer function of the sensor, which can be expressed in
factored form:
In this equation, zn are the roots of the numerator polynomial, giving
the zeros of the transfer function, and pm are the roots of the
denominator polynomial giving the poles of the transfer function.
In the calibration pack, G is the sensitivity given for each component on the
first page, whilst the roots zn and pm, together with the normalising factor A,
are given in the Poles and Zeros table. The poles and zeros given are
measured directly at Güralp Systems' factory using a spectrum analyser.
Transfer functions for the vertical and horizontal sensors may be provided
separately.
4.1.2 Frequency response curves
The frequency response of each component of the 3ESPCD is described in the
normalised amplitude and phase plots provided. The response is measured at
low and high frequencies in two separate experiments. Each plot marks the
low-frequency and high-frequency cutoff values (also known as –3 dB or
half-power points).
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