Guralp Systems CMG-3TB Manual

CMG-3TB
Operator’s guide
Part MAN-BHO-0001
Designed and manufactured by
Güralp ystems Limited
3 Midas House, Calleva Park
Aldermaston RG7 8EA
England
Proprietary Notice: The information in this manual is
proprietary to Güralp ystems Limited and may not be
copied or distributed outside the approved recipient's
organisation without the approval of Güralp ystems
Limited. Güralp ystems Limited shall not be liable for
technical or editorial errors or omissions made herein,
nor for incidental or consequential damages resulting
from the furnishing, performance, or usage of this
material.
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CMG-3TB
Table of Contents
1 Introduction............................................................................................................... 4
1.1 ystem configuration.......................................................................................... 5
1.2 Digital borehole installations............................................................................. 6
1.3 The hole lock system.......................................................................................... 7
The single-jaw hole lock...................................................................................... 7
The three-jaw hole lock........................................................................................ 9
2 Assembling the instrument.................................................................................... 11
2.1 Unpacking and packing.................................................................................... 11
2.2 Handling notes.................................................................................................. 11
2.3 Assembling the 3TB.......................................................................................... 12
2.4 Disassembling the instrument.......................................................................... 16
2.5 Control units..................................................................................................... 17
The breakout box................................................................................................ 17
Calibration...................................................................................................... 18
Mass locking and unlocking.......................................................................... 19
Centring.......................................................................................................... 19
The handheld control unit................................................................................. 19
Connections.................................................................................................... 20
ignal meter................................................................................................... 20
Calibration and control.................................................................................. 21
Banana plugs.................................................................................................. 21
The inclinometer monitor unit.......................................................................... 21
2.6 Operating the hole lock.................................................................................... 22
Engaging the hole lock....................................................................................... 23
Disengaging the hole lock.................................................................................. 24
Manual operation............................................................................................... 24
3 Installing the 3TB in a borehole............................................................................. 26
3.1 Installing a sensor with hole lock unit............................................................. 26
3.2 Installing a sensor using sand backfill............................................................. 31
Procedure............................................................................................................ 32
3.3 Assembling the winch...................................................................................... 36
3.4 Earthing a borehole sensor............................................................................... 40
Installations with AC power supplies............................................................... 40
Installations with DC power supplies................................................................ 44
External lightning protection............................................................................. 45
3.5 Levelling and centring...................................................................................... 46
3.6 Downhole orientation....................................................................................... 47
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Installing the cream! extension....................................................................... 47
Installing the reference instrument................................................................... 47
Measuring the orientation.................................................................................. 48
Applying automatic rotation.............................................................................. 53
4 Calibrating the 3TB................................................................................................. 55
4.1 The calibration pack......................................................................................... 55
Poles and zeroes................................................................................................. 56
Frequency response curves................................................................................ 57
Obtaining copies of the calibration pack........................................................... 57
4.2 Calibration methods......................................................................................... 58
4.3 Calibration with cream! ................................................................................ 58
ensor response codes........................................................................................ 62
4.4 Calibration with a handheld control unit........................................................ 62
4.5 The coil constant.............................................................................................. 63
5 Inside the 3TB......................................................................................................... 64
5.1 The sensors....................................................................................................... 64
5.2 The control system........................................................................................... 66
LOCK .................................................................................................................. 66
UNLOCK ............................................................................................................ 67
CENTRE ............................................................................................................. 69
5.3 The feedback system........................................................................................ 70
Hybrid feedback................................................................................................. 71
Conventional-response feedback....................................................................... 72
Comparisons....................................................................................................... 72
6 Connector pinouts................................................................................................... 74
7 pecifications.......................................................................................................... 76
8 Revision history...................................................................................................... 78
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CMG-3TB
1 Introduction
The CMG-3TB is a three-axis seismometer consisting of three sensors
stacked vertically in a sealed borehole sonde, designed for use in cased
boreholes with diameters between 5” / 89 mm and 9” / 229 mm.
The seismometer system is self-contained except for its 12 – 30 V
power supply, which is provided through the same cable as the
analogue data. ensor functions such as levelling and mass locking are
carried out through a surface control box.
The 3TB's sensors are sensitive to ground vibrations in the frequency
range 0.0027 – 50 Hz. It outputs analogue voltage representing ground
velocity on balanced differential lines. Each seismometer is delivered
with a detailed calibration sheet showing its serial number, measured
frequency response in both long and short period sections of the
seismic spectrum, sensor DC calibration levels, and the transfer
function in poles/zeros notation.
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1.1 Syste configuration
The CMG-3 series of seismic instruments share a number of features:
•a modular sensor sonde, which can be fitted with a single-jaw or
three-jaw holelock mechanism as required,
•a pit head installation including a breakout box, and
•a number of additional, optional control units which may be
connected to the breakout box to perform installation and
maintenance tasks.
For example, a borehole or pit installation of a CMG-3TB or 3E PB
instrument with single-jaw hole lock has the following layout:
CMG 3-series instruments are also suitable for installing in boreholes
with sand backfill. In this case no hole lock unit is necessary.
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The CMG-3V sensor is identical to the vertical-component module of
the 3TB instrument, allowing you to build mixed arrays of 3V and 3TB
sensors with identical response characteristics.
1.2 Digital borehole installations
The Güralp DM24 digitizer is available in a borehole sonde form.
Connecting a Güralp borehole instrument to a downhole digitizer
allows you to construct a true digital borehole installation. This has
several advantages over a traditional borehole setup:
•Digital signals are not subject to attenuation as they travel up to
the surface, so signals received are stronger and more reliable.
•Digitizing the data at source allows you to ensure that its origin
can be reliably traced.
•The DM24 digitizer may also be combined with an
Authentication Module within the borehole sonde, allowing you
to generate cryptographically-signed data at the point of origin.
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A digital borehole installation can be provided with R 232, R 422 or
fibre-optic links to the surface, depending on the depth of the
borehole.
When a downhole digitizer is present, it takes the place of the strain
relief unit in the borehole. The surface unit also takes a slightly
different form, with a serial connector allowing you to attach a modem
or other communications link. In this type of installation, instead of
using the surface unit to pass control signals to the sensor, all
functions can be accessed remotely via the digitizer.
If you prefer to install a stand-alone digitizer at the surface, it should
be connected to the 19-pin RECORDER socket of the breakout box.
1.3 The hole lock syste
The hole lock clamp unit in a 3TB instrument provides a stable
platform for the sensor modules mounted above and below it. It is
designed to maintain a positive pressure on the borehole casing over a
prolonged period of time without attention, and to fix the sonde in
place whilst avoiding transmitting any stresses.
Güralp ystems hole locks are constructed to order from accurate
measurements of your borehole at the depth you wish to install the
instrument. Either single-jaw or three-jaw hole lock units can be
manufactured.
In installations with sand backfill, or where the instrument rests on the
bottom of the borehole, a hole lock may be unnecessary.
The single-jaw hole lock
The single jaw hole lock is the standard option for triaxial borehole
instruments. It consists of an active clamp arm and a number of skids
or studs on the sonde body. The arm is attached to a compression
spring, which forces it to swing out from the sonde and wedge the
body against the borehole wall. A serrated steel jaw at the end of the
arm provides maximum grip against the borehole casing. The skids or
studs and the locking arm together form a multi-point clamp, which
aligns the sonde body parallel to the axis of the borehole and holds it
firmly in place so that it cannot twist or slip under the influence of
ground vibrations.
There are several configurations of skids and studs which can provide
a suitable clamp. Either
•the locking jaw pushes two steel skids against the side of the
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CMG-3TB
borehole, providing two line contacts;
•only the tips of the skids come into contact with the borehole,
providing three point contacts;
•a single skid is combined with a pad to provide one line and one
point contact; or
•three studs provide three point contacts.
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Operator's guide
tuds have the advantage of being smaller than skids, but the contact
points are very close to each other. You should evaluate the various
locking methods available to see which works best in your borehole.
The spring inside the lock provides around 60 kg of force at its locking
position. A DC actuator retracts the arm into the body of the lock so
that the sensor mechanism can be installed and removed. The actuator
consists of a 14 W DC motor with a planetary reduction gearhead,
which drives the nut of a ball lead screw through the helical drive
gears. The thread of the lead screw is prevented from turning, and so
moves linearly when the nut turns.
The motor has a power system separate from that of the sensor, and
can be controlled from the surface using a hole lock control unit. Once
the sonde is installed, the hole lock control unit may be removed.
Without power, the hole lock will not be able to retract, and the sensor
will be secured.
The three-jaw hole lock
A three-jaw hole lock is available which gives better grip on the
borehole casing, but is bulkier and heavier than the single-arm lock.
This is the standard option for uniaxial instruments; it can be installed
in boreholes between 3.5” / 89 mm and 7” / 178 mm in diameter.
The three-jaw hole lock consists of a set of three active clamp arms
attached to a compression spring, which forces them to swing out from
the sonde and wedge themselves against the borehole wall. errated
steel jaws at the end of each arm provides maximum grip against the
borehole casing. This configuration ensures that the sonde body is
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CMG-3TB
held parallel to the axis of the borehole and prevented from twisting or
slipping under the influence of ground vibrations.
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2 Asse bling the instru ent
2.1 Unpacking and packing
The 3TB seismometer is delivered in a single transportation case, with
the sensor system and hole lock mechanism (if ordered) packed
separately. The packaging is specifically designed for the 3TB 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 clean surface.
The package should contain:
•the seismometer, in sections;
•a cable to join the sensor to the breakout box;
•the breakout box;
•the hole lock control unit;
•a cable strain relief mechanism;
•a Handheld Control Unit (HCU) for monitoring sensor outputs
and calibration, if ordered; and
•a calibration data sheet.
The sensor is securely packed, and you will need to remove most of
the foam packing before it can be removed.
2.2 Handling notes
The 3TB is a sensitive instrument, and is easily damaged if
mishandled. It will not stand vertically upwards without support, and
should not be operated until it has been securely installed in a
borehole casing. If you are at all unsure about the handling or
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CMG-3TB
installation of the device, you should contact Güralp ystems for
assistance.
•Do not bump or jolt any part of the sensor when handling or
unpacking.
•Keep the sonde sections vertical wherever possible. Carry them
by hand and store in a safe rack. Never drag or roll the sonde.
•Never lay the sonde horizontally whilst the sensors are
unlocked. If the sensor system topples over, you must inform
Güralp ystems.
•Keep all the parts of the sensor system protected and clean so
that they can be joined together securely. tore in the original
packaging if possible.
•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.
2.3 Asse bling the 3TB
The 3TB is delivered in separate sections, which need to be assembled
before the instrument can be installed in a borehole. It is
recommended that you perform these steps with the help of at least
one other person.
Important: Make sure your environment is clean and dust free before
assembling the unit. tray fibres or particles cause damage to the
“O”-ring seals between the components and may render the sensor
unusable. Do not remove the protective caps on the ends of each unit
until you are ready.
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Operator's guide
1. Ensure that the “O”-ring seals on the hole lock and sensor
sections are clean and well greased.
2. tand the horizontal sensor on the ground with the packing cap
at the top, and support it to prevent it from falling over. This can
be done either by using an assistant to hold the casing steady, or
by strapping it to a support such as a bench leg.
3. Remove the packing caps from the top of the horizontal sensor
and the bottom of the hole lock unit. Beneath the caps are
connectors for the horizontal components.
4. Hold the hole lock unit above the horizontal sensor and join the
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CMG-3TB
connectors. Ensure that each is connected to its correct
counterpart.
hole lock unit at an angle above the horizontal sensor and join
the connectors. Ensure that each is connected to its correct
counterpart. The wires are fairly short, so you will need a
second person to hold the instrument whilst you connect them.
Take care not to scratch the other components when attaching
the connectors.
5. Align the hole lock unit with the NORTH mark on the
horizontal sensor housing. Doing this will allow you to check
the approximate orientation of the sensors at a glance.
The horizontal sensor consists of two distinct units (the
north/south and east/west components), which are supplied
already joined together with M3 × 8 cap screws. You should not
need to undo this connection.
If you do separate the north/south and east/west components,
make sure that both the signal cable and, if present, the pass-
through to the key switch (red and green, held in the
photograph below) are reconnected when you reassemble the
instrument.
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Operator's guide
6. Push the hole lock unit into the horizontal sensor housing,
twisting to align the holes.
7. Fit twelve M3×8 cap screws into the holes in the joint flange.
8. When all twelve screws are fitted, begin to tighten them with a
ball-ended Allen screwdriver. Tighten evenly, working round
the instrument in several passes, until the two sections are
securely joined together.
9. The vertical sensor now needs to be attached to the other end of
the hole lock. Remove the packing caps from the top of the hole
lock–actuator section and the vertical sensor.
10.Hold the vertical sensor above the hole lock–actuator section
and connect the two 15-way “D”-type connectors, as before.
Ensure that each is connected to its correct counterpart.
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CMG-3TB
11.Push the vertical sensor housing into the hole lock–actuator
section, twisting to align the holes.
12.Fit twelve M3×8 screws into the holes and tighten.
13.If you are using a single-jaw hole lock unit, attach skids or studs
to the sonde as appropriate for your installation, using the
fastenings provided.
2.4 Disasse bling the instru ent
When the instrument is recovered, you may want to disassemble it. To
do this, reverse the steps above, bearing in mind the following points:
•Make sure you only undo the screws that are necessary to
disassemble the instrument, and not the ones which hold each
module together. Each joint has several sets of screws holding it
together. Only one set from each joint needs to be undone—the
set which was added during assembly. For the joint between the
vertical sensor and the hole lock, this is the middle set of
screws; for that between the hole lock and the horizontal
sensors, it is the lower set. The joint between the two horizontal
sensors should not be dismantled.
•When you detach one module from the next, do not yank them
apart, since doing this will damage the connectors inside. Insert
flat-head screwdrivers either side of the seal, and carefully lever
both sides up simultaneously so that the modules remain
parallel. You will need someone to support the upper module as
you do this.
When the two parts are separated, tilt the upper one to gain
access to the connectors, and disconnect them without
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Operator's guide
scratching the other components.
2.5 Control units
The 3TB is operated from the surface through various control units. All
the 3TB's functions can be accessed through one or other unit. Most
can be removed from the site once the instrument is ready for use.
ome of these control units are optional and may not have been
supplied with your installation. Their functions can be duplicated
either by applying voltages directly to control lines (see appendixes for
pinout information) or through a connected Güralp digitizer such as
the CMG-DM24. The DM24 digitizer is able to pass commands to the
instrument from a Data Communications Module (DCM) or a computer
running Güralp ystems' cream! software, allowing you to access all
of the instrument's functions remotely.
The breakout box
The breakout box is normally placed where the signal cable emerges
from the borehole. It provides connectors for attaching the various
other control units, supplies power to the instrument and relays output
signals to a recorder or digitizer.
•The EN OR connector is a 32-way mil-spec plug, and should
be connected to the borehole instrument with the cable
provided.
•The RECORDER connector is a 26-way mil-spec plug. This
should be connected to an analogue data recorder or stand-alone
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CMG-3TB
digitizer. In systems using downhole digitizers, this is replaced
by a 10-way mil-spec serial connector for attaching to a Data
Communications Module (DCM), modem or other
communications link.
•The CONTROL connector is a 26-way mil-spec plug intended
for connecting to an external controller or Handheld Control
Unit, with the same pin out as the RECORDER connector.
•The POWER connector is a 10-way mil-spec plug, which should
be connected to a source of 12 – 30 V DC power, for supplying to
the borehole instrumentation. When operating the hole lock,
you should connect the Holelock Control Unit to this connector.
Because of the high voltages employed, the hole lock circuitry is
entirely isolated from the rest of the electrical systems in the
sensor and surface unit; it is not usual to power the sensor
whilst using the hole lock.
For deep-borehole installations (over 50 m) we recommend that you
use a breakout box with internal line drivers, to ensure that logic
signals are reliably transmitted to the sensor. Contact Güralp ystems
for advice.
Note: The breakout box looks very similar to other Güralp breakout
boxes. However, its internal wiring is different from that used for some
other instruments. For this reason, if you are using several instrument
types, you should mark each breakout box clearly so that it is always
used with the correct instrument.
Calibration
To calibrate the instrument, the Calibration enable line must be
activated. This operates a relay which allows a calibration signal to
flow through the transducer feedback coil. This provides an extra force
acting on the sensor masses, producing a corresponding deflection in
the output signal, which can be analysed by a control computer to
extract the seismometer's response characteristics.
Most Güralp instruments are manufactured with active-low
Calibration enable lines. However, instruments with active-high
calibration can be manufactured on request.
Mass locking and unlocking
The 3TB is delivered with its sensor masses locked, so that they will
not be damaged in transit. You should lock the masses whenever you
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Operator's guide
need to move the instrument.
To unlock the instrument, hold down the ENABLE and UNLOCK
buttons (or the UNLOCK switch on a breakout box) for at least six
seconds. The sensor's microcontroller will free the vertical, N/ and
E/W sensor masses in turn and ready them for use. Once this is done,
the controller automatically starts a centring cycle. If you issue an
UNLOCK command when the masses are already free, the instrument
will attempt to lock the masses first, and then unlock them in
sequence as normal.
To lock the instrument, hold down the ENABLE and LOCK buttons (or
the LOCK switch) for at least six seconds. The sensor's microcontroller
will lock the vertical sensor mass, followed by the N/ and E/W sensor
masses in turn. After this, the controller locks the base of the
horizontal instrument, tilting it until it is held against its end stop. The
instrument is now protected against accelerations up to 10 g , and is
ready for transportation.
Centring
To centre the instrument, hold down ENABLE and CENTRE buttons
(or the CENTRE switch) for at least six seconds. If the masses are
locked, the microcontroller will do nothing. Otherwise, it attempts to
zero the output of the vertical, E/W, and N/ sensors in sequence by
exerting a small extra force on the boom. For the vertical sensor, a
motor-driven adjuster presses a small spring lever against the boom
until the mass position output indicates an offset close to zero. In the
case of the horizontal sensors, the sensor frame is tilted on its base
plate. Again, the controller monitors the mass position sensor and
stops the centring process once it reaches its lowest offset.
After successful centring, the mass position outputs should be in the
range 0.1 – 0.8 V. If the centring process leaves the mass position
outputs above ±1.1 V, start another centring cycle. You will probably
need to perform several rounds of centring before the masses are ready.
The handheld control unit
This portable control unit provides easy access to the seismometer's
control commands, as well as displaying the output velocity and mass
position ( i.e. acceleration) on an analogue meter.
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CMG-3TB
Connections
The HCU provides
•two identical 26-pin connectors for attaching to the HCU or
RECORDER connectors of the breakout box, and
•a 10-pin connector through which you can power the
instrument, if desired. The power pins on this connector are
directly connected to those on the EN OR POWER connector
of the breakout box. When using this alternative power
connection, you should ensure you do not inadvertently connect
two power supplies together.
Signal eter
The upper section of the HCU contains a simple voltmeter for
monitoring various signals from the instrument.
•To monitor the velocity outputs, switch the dial to V, N/ or
E/W VEL according to the component you want to monitor.
•To monitor the mass position outputs, switch the dial to V, N/
or E/W MA PO according to the component you want to
monitor.
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