Download GÜRALP OCEAN BOTTOM

GÜRALP OCEAN BOTTOM
Triaxial Broadband Ocean Bottom (OBS) and
Ocean Bottom Borehole (OBH) Systems
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Broadband Frequency response
(0.00277Hz to 50Hz)
(360 second to 0.02 second)
other responses available
Sensor noise below USGS NLNM from 100
second period to 18Hz
+/- 30 degrees microprocessor controlled
leveling system. (Reduces installation
complexity)
24bit resolution internal broadband acquisition
system
Low Power <1.8 Watts includes stable real time
clock
Ultra Low Power version <0.7 Watts Option
(Consult Guralp Systems)
Real Time Clock module with exceptional
-8
stability (accuracy of <1.8*10 ) over full
temperature range
Real Time Clock stability <4 * 10-9 over 0 to 15
degrees Centigrade
Internal Power Management for operations
requiring high current surges such as leveling,
Unlocking and centering.
Autonomous Deployment system and
shutdown.
Storage 8 Gigabytes of FLASH Memory. (Ask
Guralp Systems for larger Capacity)
Firewire (IEEE1394) data transfer output port
TCP/IP protocol interface option (consumes 1
WATT extra power)
Internal 3 axis Magnetometer for Orientation
measurement.
8 or 16 Low sample rate environmental
channels 16-bit, optionally 24-bit.
Automatic Realtime Clock calibration and
synchronisation.
Disk storage system of 90 Gigabytes available
GÜRALP SYSTEMS LIMITED
3 Midas House, Calleva Park, Aldermaston,
Reading, Berks, RG7 8EA, United Kingdom.
Tel: +44 (0) 118 9819056
Fax: +44 (0) 118 9819943
e-mail: [email protected]
Website: http://www.guralp.com
Distributed By:-
Issue B: October 2001
OCEAN BOTTOM - Page 1 of 5
Guralp Systems has been designing and manufacturing specialized Ocean Bottom Systems since 1987.
Systems for Ocean bottom applications include broadband seismometers with a low-power option,
automatic tilt compensation, stable leveling platform, wide dynamic range digitizer, high stability clock,
and long duration low power recording medium. Direct communication with the ocean bottom sensor
requires a serial interface, or optical interface for high bandwidth data transfer. Manufactured Ocean bottom
systems can be fitted with serial, optical or low power long range modem interfaces. Inclusion of optional
TCP/IP interface allows OBS systems to be easily integrated into existing and future networks..
Standard ocean bottom surface housings such as BenthosTM Flask or custom made Titanium housings are
available.
The picture on the left
shows a complete OBS
system being assembled
in a Benthos Glass
sphere.
The picture on the right
shows the same complete
OBS package assembled
in a custom Grade 5
Titanium case for use at
depths up to 3500m.
Autonomous Deployment System.
The Guralp Autonomous OBS consists of a 3 component Broad Band Seismometer. The choice of
seismometer consists of CMG-1T, CMG-3T or in some cases CMG-3ESP type sensor.
The OBS system can be operated manually or as an Autonomous system featuring fully automatic
operation, i.e. Operation of the leveling platform, sensor unlock and centering on deployment followed
by an automatic check of the sensor centering on a periodic basis.
These operations are carried out by the on-board micro-controller and during periods of inactivity this
part of the system automatically enters a low-power 'sleep' mode in which the current consumption is
reduced to 500 micro-amps. Deployment is defined by simply programming the on-board real-time clock
with the correct date and time. When this time arrives the system 'wakes up' deploys the instruments and
goes back to sleep. After an hour the system will wake up and check the mass positions of the sensors
and re-centre them if necessary, before going back to sleep. As the sensors and the installation settles
down re-centring becomes less and less necessary so this period of sleep is automatically increased (up to
a maximum of 64 hours).
Wide Range Leveling System
Unlike conventional gimbal systems, the Guralp OBS
±30 degree leveling system has been designed for use
with long period broadband sensors. A set of
attachment points glued to the inside of the Benthos
sphere holds the leveling system, sensor, and digitizer
within the Benthos sphere. The platform design is
based on the natural stability of a bell and socket type
construction joint. The rotary motion of the bowl is
provided by a worm-drive driven by a dc motor. The
tilt drive is provided by a 1mm pitched lead screw
which linearly positions the bearing block on a pair of
parallel slides. The same leveling system can be easily
installed inside titanium housings as can be seen in the
picture on the right
OCEAN BOTTOM - Page 2 of 5
The operating principle and the philosophy of the levelling platform is based on the natural stability
provided by the ball and socket type construction joint. The three-component sensors are contained in a
machined cavity inside a structure that resembles an inverted dome whose exterior is machined to a
spherical form. The unit rests in a ring shaped bearing so that the dome can move freely in azimuth and tilt
directions.
A metal post, mounted centrally under the dome, carries a machined ball which articulates with a cylindrical
cavity in a driving block below it. The driving block, moving on a plane surface below the dome effectively
translates the position of the dome expressed in spherical co-ordinates into positions on a plane expressed in
polar co-ordinates. The described position mechanism consists of a turntable and a lead screw to drive the
central block
The described mechanism is more stable and more compact than the more usual gimbal arrangement and
also has fewer moving parts. For broadband OBS seismometer applications the gimbal arrangement is
believed to be the most time stable mechanical construction..
The rotary motion of the bowl is provided by a worm-drive driven by a dc motor. The tilt drive is provided
by a 1 mm pitched lead screw which linearly positions the bearing block on a pair of parallel slides. The
lead screw is also driven by a dc motor. Linear displacement transducers with limit switches ensure the
precise positioning of the leveling system.
The required method of zeroing the bowl tilt is carried out by the radial and azimuth adjustments being
done until the 2 axes inclinometer outputs are brought as close to zero as possible. The radial offset tilt
magnitude is calculated from the X, Y readings of the inclinometer and the azimuth position is determined
from the sign information of the inclinometers.
The picture shows a complete OBS system assembled with the leveling platform. The
sensor system is completely self-contatined unit which can level itself automatically
over +/- 30 degrees. The acquisition system is based on the CMG-DM24 which is
capable of controlling ALL of the OBS functions and providing full state of health
information about the sensor package to the user. As well as the 24-bit ADC there are
two more multi-plexed digitizers on 16-bit and one 10-bit, to digitize the mass
positions, inclinometers outputs, leveling bowl displacement transducer outputs, Real
time clock module, internal temperature and pressure sensor outputs. Optionally a
flux gate magnetometer can be installed within the sensor housing to establish
magnetic North
OCEAN BOTTOM - Page 3 of 5
Low Power Operation
A low power option can be installed on all Guralp sensors. Components are hand-selected and
decrease sensor power to 30 mA at 12 Vdc or25 mA at ±5 Vdc as shown below. The lowest
achieved to date is 23mA. Reduction of the full-scale output to ±4.5 V decreases the sensor dynamic
range compared to the ±10 V output. With Guralp systems new ultra low power CMG-DM24 for
OBS applications the complete system can be operated with a power consumption of less than 0.7
Watts (please consult the factory for more information about an Ultra low power system).
The glass sphere with sensor, digitizer, control electronics and high-stability clock uses <1.8 Watts
at +12 Vdc. The system can accept 12-36 Vdc from the user's power supply.
Real Time Clock Module
This self-contained module is designed to provide a
precision timebase and real time clock for precision data
acquisition systems e.g. Ocean Bottom Seismometers.
The unit contains a microprocessor controlled temperature
compensated quartz oscillator and real time clock counters,
which can be synchronized to UTC using GPS, and will then
maintain time-keeping to an accuracy of 2*10-8 using a builtin Lithium primary cell.
The unit provides several different output frequencies and
real time calendar clock (in BCD format) via I2C bus. The
unit runs from the system 5volt logic supply in normal use
and only uses the internal battery for standby operation between system setup and test and deployment.
Specialised Housings.
TM
Units can be supplied as standard in 17” Benthos Glass Spheres, Grade 5 Titanium cases or any
other customized casing enclosure desired. Full pressure testing is available on casings at additional
cost.
Picture showing 3 CMG-1TD
OBH units before delivery to
customer. U nits are supplied in
Guralp designed Titanium cases
which were designed for 10,000
meters pressure tested to 8,800
meters pressure. The
seismometers are CMG-1T units
with a 360 second response, the
data is digitised within the
package by the CMG-DM24, 3
channel 24-bit broadband
borehole ADC, with 8 16-bit
channels providing all of the
environmental information for
the system.
A CMG-1TD OBDS system before delivery to customer. Unit
is cased in Stainless Steel designed by Guralp systems for
deployment at depth up to 6000 m. The sensor is a 360 second
CMG-1T, the data is digitized within the package by the
CMG-DM24, 3 channel 24-bit broadband borehole ADC,
with 8 16-bit channels providing all of the environmental
information for the system.
OCEAN BOTTOM - Page 4 of 5
OBS / OBH data storage unit.
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External disk storage unit (SAM) with 90 Gigabytes of disk storage available
ROV removable
The Güralp OBS CMG-SAM Storage Acquisition Module accepts up to six multi-component digital
data streams (as from Güralp OBS & OBH sensor/digitizer units), writes the data to its internal silicon
file data buffer (64Mb FLASH memory) , and then archives data from the silicon file to multiple
internal miniture low power SCSI hard disks,
Data is stored on the disk in GCF format (Guralp Compressed Format). GCF uses a difference
algorithm to express all data as 32, 16 or 8 bit differences, depending on the dynamic range required
for the data block. This gives the advantages of reducing baud rates and storage requirements when
compared to non-compressed data format.
The power consumption of the OBS CMG-SAM unit is <1.4 watts mean when acquiring and storing 3
components @100 sps data with environmental channel data in a 24 hour period.
Related Documents:
Real Time clock module
Autonomous OBS guide
CMG-1T OBS operation manual
CMG-1T datasheet
CMG-3T datasheet
CMG-3ESP datasheet
OCEAN BOTTOM - Page 5 of 5