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Operator's guide

1.1 System configuration

The CMG-3 series of seismic instruments share a number of features:

•

a modular sensor sonde, which can be fied with a single-jaw or

three-jaw holelock mechanism as required,

•

a pit head installation including a surface control unit, and

•

a number of additional, optional control units which may be

connected to the surface control unit to perform installation and

maintenance tasks.

For example, a borehole or pit installation of a CMG-3V or 3ESPV

instrument with a three-jaw hole lock has the following layout:

CMG 3-series instruments are also suitable for installing in boreholes

with sand backfll. In this case no hole lock unit is necessary.

December 2004

Содержание CMG-3V

Страница 1: ...manual is proprietary to G ralp Systems Limited and may not be copied or distributed outside the approved recipient s organisation without the approval of G ralp Systems Limited G ralp Systems Limite...

Страница 2: ...20 Disengaging the hole lock 21 Manual operation 21 3 Installing the 3V in a borehole 22 3 1 Installing a sensor with hole lock unit 22 3 2 Installing a sensor using sand backfll 27 Procedure 28 3 3...

Страница 3: ...Operator s guide CENTRE 53 5 3 The feedback system 55 Hybrid feedback 56 Conventional response feedback 58 Comparisons 59 Appendix A Connector pinouts 60 Appendix B Specifcations 62 December 2004 3...

Страница 4: ...hrough a surface control box The 3V s sensor is sensitive to ground vibrations in the frequency range 0 0027 50 Hz depending on the options you have specifed It outputs analogue voltage representing g...

Страница 5: ...a surface control unit and a number of additional optional control units which may be connected to the surface control unit to perform installation and maintenance tasks For example a borehole or pit...

Страница 6: ...r is available in a borehole sonde form Connecting a G ralp 3 series instrument to a downhole digitizer allows you to construct a true digital borehole installation This has several advantages over a...

Страница 7: ...le lock clamp unit in a 3V 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 prolonge...

Страница 8: ...e which is smaller and lighter than the three jaw lock but does not grip the borehole casing with as much force The single jaw hole lock is the standard option for triaxial borehole instruments It con...

Страница 9: ...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 throu...

Страница 10: ...the sensor to the surface control box the surface control unit the hole lock control unit if ordered a cable strain relief mechanism if ordered a Handheld Control Unit HCU for monitoring sensor outpu...

Страница 11: ...ctions 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 you...

Страница 12: ...her control units supplies power to the instrument and relays output signals to a recorder or digitizer In addition the unit contains state of health SOH electronics for the sensor and a diferential i...

Страница 13: ...the hole lock The borehole control unit is supplied with a 3 m cable as standard This can be extended up to 100 m without compromising signal quality The sensor uses amplifers with high common mode re...

Страница 14: ...tal signals are sent to the sensor which is particularly useful for deep borehole installations Systems including a downhole digitizer generally do not require a 3VIC instrument since the motors can b...

Страница 15: ...tor driven adjuster presses a small spring lever against the boom until the mass position output indicates an ofset close to zero Afer successful centring the mass position outputs should be in the ra...

Страница 16: ...ides two identical 26 pin connectors for aiaching t o t he HCU or RECORDER connectors of the Surface Control Unit and a 10 pin connector through which you can power the instrument if desired The power...

Страница 17: ...tion lines controls the instrument s mass control system To initiate locking unlocking or centring hold down the ENABLE switch on the HCU together with the appropriate switch for the command you want...

Страница 18: ...ensor is in use 3 Read of the X and Y components of the tilt from the analogue meters 4 If both tilts are within the green shaded region the instrument is close enough to vertical that it can be level...

Страница 19: ...DC power supply across the input terminals of the hole lock control unit The hole lock control unit supplied in regions with 220 V AC mains power difers from that supplied for 110 V AC mains power Yo...

Страница 20: ...EXTEND JAW position 3 When the lock arm reaches its fully extended position the motor will automatically stop and the current will drop to 0 A If using a deep borehole unit return the dial to zero 4 I...

Страница 21: ...otor is now working against the spring 3 When the lock arm reaches its fully retracted position the motors will automatically stop and the current will drop to 0 A If using a deep borehole unit return...

Страница 22: ...if possible or measure out the cable beforehand Most installations are equipped with a strain relief unit which consists of a metal arm that swings out from the load bearing cable to wedge against th...

Страница 23: ...Unit and Holelock Control Unit and aiempt to retract the hole lock arm see Section 2 5 Operating the hole lock If this fails you should contact G ralp Systems Extend the arm once more 3 Fix the main...

Страница 24: ...CMG 3V 4 Aiach the lifing loop to the sensor using four M5M16 screws provided 24...

Страница 25: ...d the strain relief mechanism 8 Position the assembly over the top of the borehole Do not allow it to drag across the ground 9 Lower the sonde so that its base is just level with the borehole mouth If...

Страница 26: ...ed depth At approximately 20 m intervals fx the signal cable to the load bearing cable using metal clamps nylon cable ties every 5 m may be sufcient for shallow installations This will ensure that the...

Страница 27: ...l type of sand to use is the fne kiln dried s and used for children s play sandpits This is readily available in airtight bags is thoroughly washed and clean and will contain liile sediment When dried...

Страница 28: ...lume of the unit which is to be installed in the borehole The volume of a cylinder v r2 h Also measure the internal diameter of the borehole 2 Measure and pour in a sufcient quantity o f sand to fll t...

Страница 29: ...strain relief mechanism and run the signal cable through the mechanism using the built in clamps without tightening them Do not allow the signal cable to bear any of the sensor s weight 5 Aiach the li...

Страница 30: ...ith t he s train r elief mechanism extended Tighten the cable clamps on the strain relief unit allowing a liile slack in the signal cable 8 Fix the signal cable to the main lifing cable about 1 m abo...

Страница 31: ...the sensor down the borehole keeping track of the depth reached 13 At approximately 20 m intervals fx the signal cable to the load bearing cable using metal clamps nylon cable ties every 5 m may be s...

Страница 32: ...f the instrument determined in step 1 17 Pour this sand into the borehole If you can check how much of the sensor is covered with sand Do not overfll the hole 18 Carefully slacken the load bearing cab...

Страница 33: ...ons all the way into the head with the retaining tape loops facing outwards 2 If you are working on a surface of sand or soil rotate the feet so that the points face downwards lef For rock or other ha...

Страница 34: ...is not provided you can make one by untwisting three outer strands from the 7 core cable crossing the two sets and pleating the three outside strands back around the remaining four in the opposite dir...

Страница 35: ...e legs in turn to the height you require fnishing at the leg with the winch aiached 7 Take the end of the load bearing cable without the loop and screw it to the axle inside the winch using a 4 mm All...

Страница 36: ...sten it in place with a collar washer and screw using the larger Allen key 9 Wind the cable onto the winch by rotating the handle Ensure that the cable builds up neatly across the drum Continue windin...

Страница 37: ...DOWN direction to free the cable 10 Remove the handle and screw it onto the metal spool of the ratchet mechanism 11 Hang the strain relief unit and instrument s from the loop at the other end of the c...

Страница 38: ...en it and the power supply for the instrument This will allow full control of the local grround A spark gap surge protector should also be installed on the mains side of the transformer so that transi...

Страница 39: ...e itself For this to work the borehole must have a conductive casing and be situated close 30 m to the surface installation In such an installation you need only connect a cable green wire in the phot...

Страница 40: ...thout any further action Fresh water is an inferior conductor In a dry or sand flled borehole or one with a non conducting casing you will need to ensure the sonde is grounded by some other means The...

Страница 41: ...nsor s lifing loop with a metallic clamp as shown below This provides an additional frm contact between the sonde and the load bearing cable Installations with downhole digitizers will need similar ar...

Страница 42: ...he enclosure any coupling between this sensor local earth line and ground lines for other parts of the system must be minimized Installations with DC power supplies G ralp sensors require a 24 V DC po...

Страница 43: ...or a wind generator In these cases the power supply may already have protection from transients installed in which case you may not need such comprehensive protection although some form of protection...

Страница 44: ...hin the green shaded region the instrument is close enough to vertical that it can be levelled and centred successfully If either output is in the red shaded region you should not aiempt t o u nlock o...

Страница 45: ...ssful centring the mass position outputs should be in the range 0 1 0 8 V 9 If the centring process leaves the mass position outputs above 1 1 V repeat steps 4 and 5 You will probably need to initiate...

Страница 46: ...ach a steady state for low frequencies this may take a long time In addition several measurements must be made to determine the response over the full frequency spectrum Injecting white noise into the...

Страница 47: ...gnal combined with the sensors own measurements If you cannot see the calibration signal zoom into the WaveView using the scaling icons at the top lef of the window or the cursor keys 4 If you need to...

Страница 48: ...nverted to a velocity function by dividing by the angular frequency of the calibration signal v a 2 f V 2 f R K This voltage is the equivalent input velocity 12 Compare the equivalent input velocity w...

Страница 49: ...response to gravity To do this you will need a mounting harness for the sonde and apparatus for measuring tilt angles accurately 1 Measure the acceleration due to gravity g at your location 2 Tilt the...

Страница 50: ...from any pressure variations in the atmosphere The 3V functions by monitoring the position of the mass with a capacitative position sensor Signals from the sensor are fed into an electronic processing...

Страница 51: ...s are sent as single ended circuits referred to analogue ground on the output plug The 3V also receives control signals which are used to clamp and unclamp the masses and to run the motors which level...

Страница 52: ...ree lines are high the control microprocessor goes into a power saving mode In routine operation the lines are controlled from the breakout box Handheld Control Unit or digitizer If you send control s...

Страница 53: ...locked 2 The instrument checks the sensor base 3 The mass is unlocked 4 The sensor base is unlocked This process takes longer Afer u nlocking t he i nstrument a utomatically p erforms a r ound o f ce...

Страница 54: ...tion of the Z component comes within range and is centred The pulses become more brief as this goes on until a pulse is missed signifying that no corrective impulse is needed 7 The N S and E W compone...

Страница 55: ...s to force the mass back toward equilibrium The feedback loop has a sufciently high gain to cancel the motion of the mass Since the mass is not moving the forces acting on it must be balanced the feed...

Страница 56: ...or should always be operated with the displacement transducer centred or nulled so that the response to input acceleration is linear There are two types of feedback system which can be used in a 3V in...

Страница 57: ...r can be provided upon request Hybrid feedback systems provide a stable response particularly for portable systems with a high saturation level at high frequencies and a high dynamic range at long per...

Страница 58: ...stor This arrangement results in two poles at specifed frequencies The velocity response of a conventional response system is defned by a transfer function identical to that of a conventional long per...

Страница 59: ...ow p lot t he c omparative r esponse o f a conventional velocity output broadband sensor and a hybrid output broadband sensor The lef hand graph shows the response in terms o f output against input ac...

Страница 60: ...breakout box a 32 way mil spec plug 02E 19 32P Column c The RECORDER and HCU connectors on the breakout box both 26 way mil spec plugs 02E 16 26P Column d The POWER connector on the breakout box a 10...

Страница 61: ...Note The velocity acceleration mode switch pin is used by the automatic centring process to switch the instrument temporarily into a mode where its response at normal frequencies is fat to accelerati...

Страница 62: ...ty sensitivity 2 M 1000 V m s Mass position sensitivity 1000 V m s2 Controls Mass locking and unlocking remotely operated Mass centring automatic microprocessor controlled Mechanics and electronics Se...

Страница 63: ...frequency response value e g for a 30 s sensor the value of spec would be 30 s 0 033 Hz Sensors are available with a range of sensitivities between 2 M 750 and 2 M 10 000 V m s Because centring locki...

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